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| ImageFile = Paclobutrazol 2S, 3S isomer.svg
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| IUPACName = (2''S'',3''S'')-1-(4-Chlorophenyl)-4,4-dimethyl-2-(1H-1,2,4-triazol-1-yl)-3-pentanol
| IUPACName = (2''RS'',3''RS'')-1-(4-Chlorophenyl)-4,4-dimethyl-2-(1H-1,2,4-triazol-1-yl)-3-pentanol
| OtherNames = PP333
| OtherNames = PP333
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'''Paclobutrazol''' ('''PBZ''') is the [[International Organization for Standardization|ISO]] [[trivial name|common name]] for an [[organic compound]] that is used as a a [[Plant growth regulator|plant growth retardant]] and [[triazole]] [[fungicide]].<ref>{{cite web |url=https://pesticidecompendium.bcpc.org/paclobutrazol.html |title=Compendium of Pesticide Common Names: paclobutrazol |publisher=[[British Crop Production Council|BCPC]]}}</ref><ref name=Wakjira>{{Cite journal|url=https://doi.org/10.1080/23311932.2018.1525169|title=A review on: Response of crops to paclobutrazol application|first=Wakjira|last=Tesfahun|editor-first=Fatih|editor-last=Yildiz|date=January 1, 2018|journal=Cogent Food & Agriculture|volume=4|issue=1|pages=1–9|doi=10.1080/23311932.2018.1525169|s2cid=134517280|doi-access=free}}</ref> It is a known [[antagonist]] of the [[plant hormone]] [[gibberellin]], acting by inhibiting [[gibberellin]] [[biosynthesis]], reducing [[Internode (botany)|internodal]] growth to give stouter stems, increasing root growth, causing early fruitset and increasing seedset in plants such as [[tomato]] and [[Capsicum|pepper]]. PBZ has also been shown to reduce [[frost]] sensitivity in plants. Moreover, paclobutrazol can be used as a chemical approach for reducing the risk of [[lodging (agriculture)|lodging]] in [[cereal]] crops. PBZ has been used by [[arborist]]s to reduce shoot growth and shown to have additional positive effects on [[tree]]s and [[shrub]]s. Among those are improved resistance to [[drought]] stress, darker green leaves, higher resistance against fungi and [[bacteria]], and enhanced development of roots. [[Meristem|Cambial]] growth, as well as shoot growth, has been shown to be reduced in some tree species.
'''Paclobutrazol''' ('''PBZ''') is a [[Plant growth regulator|plant growth retardant]] and [[triazole]] [[fungicide]]. It is a known [[antagonist]] of the [[plant hormone]] [[gibberellin]] acting by inhibiting [[gibberellin]] [[biosynthesis]], reducing [[Internode (botany)|internodal]] growth to give stouter stems, increasing root growth, causing early fruitset and increasing seedset in plants such as [[tomato]]<ref>{{cite journal | doi = 10.1023/A:1006300326975 | title = Physiological response and yield of paclobutrazol treated tomato plants (Lycopersicon esculentum Mill.) | year = 2000 | last1 = Berova | first1 = Malgorzata | last2 = Zlatev | first2 = Zlatko | journal = Plant Growth Regulation | volume = 30 | issue = 2 | pages = 117| s2cid = 30219558 }}</ref> and [[Capsicum|pepper]].<ref name=Grossi>{{cite journal | author = Grossi | title = Effects of paclobutrazol on growth and fruiting characteristics of ''Pitanga'' ornamental pepper | journal = Acta Horticulturae | year = 2005 | volume = 683 | issue = 683 | pages = 333–336 | display-authors = 1 | author2 = <Please add first missing authors to populate metadata.>| doi = 10.17660/ActaHortic.2005.683.41 | s2cid = 90322526 | url = https://semanticscholar.org/paper/4c08d23a7117789170c9036a52396cc4f2156f48 }}</ref> PBZ has also been shown to reduce [[frost]] sensitivity in plants. Moreover, paclobutrazol can be used as a chemical approach for reducing the risk of [[lodging (agriculture)|lodging]] in [[cereal]] crops.<ref name="Kamran-et-al-2017">{{cite journal | last1=Kamran | first1=Muhammad | last2=Cui | first2=Wenwen | last3=Ahmad | first3=Irshad | last4=Meng | first4=Xiangping | last5=Zhang | first5=Xudong | last6=Su | first6=Wennan | last7=Chen | first7=Junzhi | last8=Ahmad | first8=Shakeel | last9=Fahad | first9=Shah | last10=Han | first10=Qingfang | last11=Liu | first11=Tiening | title=Effect of paclobutrazol, a potential growth regulator on stalk mechanical strength, lignin accumulation and its relation with lodging resistance of maize | journal=[[Plant Growth Regulation]] | publisher=[[Springer Science+Business Media|Springer]] | volume=84 | issue=2 | date=2017-11-08 | issn=0167-6903 | doi=10.1007/s10725-017-0342-8 | pages=317–332| s2cid=52322462 }}</ref> PBZ has been used by [[arborist]]s to reduce shoot growth and shown to have additional positive effects on [[Tree|trees]] and [[shrub]]s. Among those are improved resistance to [[drought]] stress, darker green leaves, higher resistance against fungi and [[bacteria]], and enhanced development of roots.<ref>Chaney ''et al.'' 1996{{vague|date=December 2011}}</ref><ref>{{cite journal |last1=Fletcher |first1=R. Austin |last2=Gilley |first2=Angela |last3=Sankhla |first3=Narendra |last4=Davis |first4=Tim D. |title=Triazoles as Plant Growth Regulators and Stress Protectants |journal=Horticultural Reviews |date=2010 |pages=55–138 |doi=10.1002/9780470650776.ch3 |publisher=John Wiley & Sons, Ltd |isbn=9780470650776 |language=en}}</ref><ref>{{cite journal |last1=Rademacher |first1=Wilhelm |title=Growth Retardants: Effects on Gibberellin Biosynthesis and Other Metabolic Pathways |journal=Annual Review of Plant Physiology and Plant Molecular Biology |date=June 2000 |volume=51 |issue=1 |pages=501–531 |doi=10.1146/annurev.arplant.51.1.501|pmid=15012200 }}</ref><ref>Chaney 2003{{vague|date=December 2011}}</ref> [[Meristem|Cambial]] growth, as well as shoot growth, has been shown to be reduced in some tree [[species]].<ref>{{Cite journal|url=http://doi.org/10.48044/jauf.2004.017|title=Response of Cambial and Shoot Growth in Trees Treated with Paclobutrazol|first1=Shuju|last1=Bai|first2=William|last2=Chaney|first3=Yadong|last3=Qi|date=May 1, 2004|journal=Arboriculture & Urban Forestry|volume=30|issue=3|pages=137–145|doi=10.48044/jauf.2004.017|s2cid=174943}}</ref>
== Structure and synthesis ==
== Structure and synthesis ==
The first [[Total synthesis|synthesis]] of paclobutrazol was disclosed in [[Patent|patents]] filed by an [[Imperial Chemical Industries|ICI]] group working at [[Jealott's Hill]].<ref>{{cite patent |country=GB |number=1595696 |status=patent |gdate=1981-08-12 |fdate=1976-08-19 |pridate=1976-08-19 |invent1 =Boize, L.M. |invent2 =Sugavanam, B. |invent3 = Shephard, M.C. |invent4 = Batch, J.J. |title=Triazoles and imidazoles useful as plant fungicides and growth regulating agents |assign1=ICI Ltd}}</ref>
The first [[Total synthesis|synthesis]] of paclobutrazol was disclosed in [[Patent|patents]] filed by an [[Imperial Chemical Industries|ICI]] group working at [[Jealott's Hill]].<ref>{{cite patent |country=GB |number=1595696 |status=patent |gdate=1981-08-12 |fdate=1976-08-19 |pridate=1976-08-19 |invent1 =Boize, L.M. |invent2 =Sugavanam, B. |invent3 = Shephard, M.C. |invent4 = Batch, J.J. |title=Triazoles and imidazoles useful as plant fungicides and growth regulating agents |assign1=ICI Ltd}}</ref>
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In a 1984 study, [[Imperial Chemical Industries|ICI]] workers separated the individual [[enantiomer]]s by [[chiral resolution]] and were able to demonstrate that only the (2''R'',3''R'') isomer displays substantial [[Fungicide|fungicidal]] activity, whereas the (2''S'',3''S'') isomer is responsible for the growth regulating properties. However, the commercial product (developed under the code number PP333) was the [[Racemic mixture|racemic]] material, since separation of the isomers was unnecessary when both components had utility in [[agriculture]].<ref name=Suga/>
In a 1984 study, [[Imperial Chemical Industries|ICI]] workers separated the individual [[enantiomer]]s by [[chiral resolution]] and were able to demonstrate that only the (2''R'',3''R'') isomer displays substantial [[Fungicide|fungicidal]] activity, whereas the (2''S'',3''S'') isomer is responsible for the growth regulating properties. However, the commercial product (developed under the code number PP333) was the [[Racemic mixture|racemic]] material, since separation of the isomers was unnecessary when both components had utility in [[agriculture]].<ref name=Suga/>
== Mechanism of action ==
== Mechanism of action ==
Paclobutrazol is an inhibitor of enzymes which use [[cytochrome P450]] as a co-factor. Their [[active site]] contains a [[heme]] center which activates oxygen from the air to oxidise their [[Substrate_(chemistry)#Biochemistry|substrate]]s. The (2''S'',3''S'') isomer inhibits the enzyme [[ent-kaurene oxidase]]<ref name=Suga/><ref>{{cite journal |doi=10.1104/pp.103.032706 |title=The Pea Gene LH Encodes ent-Kaurene Oxidase |year=2004 |last1=Davidson |first1=Sandra E. |last2=Smith |first2=Jennifer J. |last3=Helliwell |first3=Chris A. |last4=Poole |first4=Andrew T. |last5=Reid |first5=James B. |journal=Plant Physiology |volume=134 |issue=3 |pages=1123–1134 |pmid=14988475 |pmc=389936 }}</ref> which is on the main biosynthetic pathway to [[gibberellin]]s, which are important plant hormones.<ref>{{cite journal |doi=10.1093/pcp/pcaa092 |title=The Current Status of Research on Gibberellin Biosynthesis |year=2020 |last1=Hedden |first1=Peter |journal=Plant and Cell Physiology |volume=61 |issue=11 |pages=1832–1849 |pmid=32652020 |pmc=7758035 }}</ref> The (2''R'',3''R'') isomer is a better fit to the active site of the fungal [[cytochrome P450 14α-demethylase]]. This inhibits the conversion of [[lanosterol]] to [[ergosterol]], a component of the fungal cell membrane, which is lethal for many species.<ref name=Suga/> Many other azole derivatives including [[propiconazole]] and [[tebuconazole]] show this type of activity, so the main commercial opportunity for paclobutrazol was as a plant growth retardant and it was first marketed by ICI in 1985 under the [[brand name|trade names]] Bonzi, Cultar and Parlay.<ref name=PPDB/>
Paclobutrazol is an inhibitor of enzymes which use [[cytochrome P450]] as a co-factor. Their [[active site]] contains a [[heme]] center which activates oxygen from the air to oxidise their [[Substrate_(chemistry)#Biochemistry|substrate]]s. The (2''S'',3''S'') isomer inhibits the enzyme [[ent-kaurene oxidase]]<ref name=Suga/><ref>{{cite journal |doi=10.1104/pp.103.032706 |title=The Pea Gene LH Encodes ent-Kaurene Oxidase |year=2004 |last1=Davidson |first1=Sandra E. |last2=Smith |first2=Jennifer J. |last3=Helliwell |first3=Chris A. |last4=Poole |first4=Andrew T. |last5=Reid |first5=James B. |journal=Plant Physiology |volume=134 |issue=3 |pages=1123–1134 |pmid=14988475 |pmc=389936 }}</ref> which is on the main biosynthetic pathway to [[gibberellin]]s, which are important plant hormones.<ref>{{cite journal |last1=Rademacher |first1=Wilhelm |title=Growth Retardants: Effects on Gibberellin Biosynthesis and Other Metabolic Pathways |journal=Annual Review of Plant Physiology and Plant Molecular Biology |date=June 2000 |volume=51 |issue=1 |pages=501–531 |doi=10.1146/annurev.arplant.51.1.501|pmid=15012200 }}</ref><ref>{{cite journal |doi=10.1093/pcp/pcaa092 |title=The Current Status of Research on Gibberellin Biosynthesis |year=2020 |last1=Hedden |first1=Peter |journal=Plant and Cell Physiology |volume=61 |issue=11 |pages=1832–1849 |pmid=32652020 |pmc=7758035 }}</ref> A secondary effect arising from the inhibition of ent-kaurene oxidase is that its precursor, [[geranylgeranyl pyrophosphate]] accumulates in the plant and some of this is diverted into additional production of the [[phytol]] group of [[chlorophyll]] and the hormone [[abscisic acid]]. The latter is responsible for controlling [[transpiration]] of water through the leaves and hence PBZ treatment can lead to better tolerance of drought conditions.<ref name=Desta>{{Cite journal|url=https://doi.org/10.1186/s40538-020-00199-z|title=Paclobutrazol as a plant growth regulator|first1=Bizuayehu|last1=Desta|first2=Getachew|last2=Amare|date=January 7, 2021|journal=Chemical and Biological Technologies in Agriculture|volume=8|issue=1|doi=10.1186/s40538-020-00199-z|doi-access=free|s2cid=230796693}}</ref> The (2''R'',3''R'') isomer is a better fit to the active site of the fungal [[cytochrome P450 14α-demethylase]]. This inhibits the conversion of [[lanosterol]] to [[ergosterol]], a component of the fungal cell membrane, which is lethal for many species.<ref name=Suga/> Many other azole derivatives including [[propiconazole]] and [[tebuconazole]] show this type of activity, so the main commercial opportunity for paclobutrazol was as a plant growth retardant and it was first marketed by ICI in 1985 under the [[brand name|trade names]] Bonzi, Clipper, Cultar and Parlay.<ref name=PPDB/><ref name=BCPC8>{{Cite book |isbn=0948404019 | title = The Pesticide Manual - A World Compendium | edition = Eighth | editor = Worthing C.R. | publisher = British Crop Protection Council | date = 1987|pages=628–629}}</ref>
== Usage==
As an antagonist of gibberellin biosynthesis, PBZ has a growth retardant effect on most plant species.<ref name=Desta/> It is absorbed by plant tissues and transported via the [[xylem]] to the growing parts, where the rate of cell division is reduced compared to untreated plants and the new cells do not elongate.<ref name=BCPC8/><ref name=MDAR>{{cite web|title=Active Ingredient Paclobutrazol: Review Conducted by MDAR and MassDEP for Use in Sensitive Areas of Rights-of-Way in Massachusetts.|date=January 2012|url=https://www.mass.gov/doc/paclobutrazol-review-jan-2012pdf/download?_ga=2.169004968.820722649.1646429016-1603828005.1646429016|accessdate=4 February 2022}}</ref>{{rp|5}}
===Ornamental crops===
PBZ is used in [[horticulture]], especially for glasshouse-reared perennial plants.<ref>{{Cite magazine |url=https://www.fine-americas.com/wp-content/uploads/2022/01/PGR_Guide_2022-2023.pdf |work=GrowerTalks |title=Wide Assortment of Available PGRs |last=Whipker|first=Brian E.|date=2022|pages=10–12|website=|publisher=Ball Publishing|access-date=2022-04-06}}</ref><ref>{{Cite magazine |url=https://www.fine-americas.com/wp-content/uploads/2022/01/PGR_Guide_2022-2023.pdf |work=GrowerTalks |title=Growth Regulators for Containerized Herbaceous Perennial Plants |last=Latimer|first=Joyce G.|date=2022|pages=14–60|website=|publisher=Ball Publishing|access-date=2022-04-06}}</ref>
===Trees and shrubs===
The ability of PBZ to reduce the growth of trees and shrubs means that it has found use in areas where there is a need to moderate such growth, for example under electric power lines and where a right-of-way is to be maintained. A single application of the growth regulator can give season-long control.<ref name=MDAR/><ref>{{Cite journal|url=http://doi.org/10.48044/jauf.2004.017|title=Response of Cambial and Shoot Growth in Trees Treated with Paclobutrazol|first1=Shuju|last1=Bai|first2=William|last2=Chaney|first3=Yadong|last3=Qi|date=May 1, 2004|journal=Arboriculture & Urban Forestry|volume=30|issue=3|pages=137–145|doi=10.48044/jauf.2004.017|s2cid=174943}}</ref>


===Fruit and vegetables===
== Efficacy ==
PBZ is used to increase the quantity and quality of orchard fruit and of vegetables. The quality is measured by elevated amounts of [[carbohydrate]]s, [[total soluble solids]] (TSS), the TSS/[[titratable acid]]ity ratio and a decreased acidity.<ref name=Desta/> It stimulates the growth of roots and stems and maintains the number of the leaves but suppresses the height of the plants.<ref>{{cite journal | doi = 10.1023/A:1006300326975 | title = Physiological response and yield of paclobutrazol treated tomato plants (Lycopersicon esculentum Mill.) | year = 2000 | last1 = Berova | first1 = Malgorzata | last2 = Zlatev | first2 = Zlatko | journal = Plant Growth Regulation | volume = 30 | issue = 2 | pages = 117| s2cid = 30219558 }}</ref><ref>{{Cite journal|title=Paclobutrazol induces tolerance in tomato to deficit irrigation through diversified effects on plant morphology, physiology and metabolism|first1=Sikander|last1=Pal|first2=Jiangsan|last2=Zhao|first3=Asif|last3=Khan|first4=Narendra Singh|last4=Yadav|first5=Albert|last5=Batushansky|first6=Simon|last6=Barak|first7=Boris|last7=Rewald|first8=Aaron|last8=Fait|first9=Naftali|last9=Lazarovitch|first10=Shimon|last10=Rachmilevitch|date=December 22, 2016|journal=Scientific Reports |volume=6 |issue=1 |pages=39321 |doi=10.1038/srep39321 |pmid=28004823 |pmc=5177942 |bibcode=2016NatSR...639321P}}</ref><ref name=Grossi>{{cite journal | author = Grossi | title = Effects of paclobutrazol on growth and fruiting characteristics of ''Pitanga'' ornamental pepper | journal = Acta Horticulturae | year = 2005 | volume = 683 | issue = 683 | pages = 333–336 | display-authors = 1 | author2 = <Please add first missing authors to populate metadata.>| doi = 10.17660/ActaHortic.2005.683.41 | s2cid = 90322526 | url = https://semanticscholar.org/paper/4c08d23a7117789170c9036a52396cc4f2156f48 }}</ref>
A study was conducted which compared the efficacy of paclobutrazol and [[uniconazole]] on four different plant species (''[[Petunia × atkinsiana|Petunia hybrida]]'' Vilm., ''[[Salvia splendens]]'' Sello ex Nees, ''[[Tagetes erecta]]'' L., and  [[Impatiens walleriana|''Impatiens'' L. ''wallerana'']] Hook.).<ref name="auto2">{{Cite journal|url=https://journals.ashs.org/hortsci/view/journals/hortsci/27/8/article-p896.xml|title=Efficacy of Paclobutrazol and Uniconazole on Four Bedding Plant Species|first1=James E.|last1=Barrett|first2=Terril A.|last2=Nell|date=August 1, 1992|journal=HortScience|volume=27|issue=8|pages=896–897|via=journals.ashs.org|doi=10.21273/HORTSCI.27.8.896}}</ref> Uniconazole is another triazole-containing plant growth inhibitor.<ref>T. Yokota, „New Comprehensive Biochemistry, Chapter 12 - Brassinosteroids,“ Elsevier, Vol.33, pp. 277-293</ref> The plants received 10 – 160 mg/L paclobutrazol or uniconazole as a spray. For the plants salvia, marigold and impatiens, the results showed that the higher the [[concentration]] of paclobutrazol or uniconazole, the smaller the size of the plant. However, there was no link between a high paclobutrazol concentration and a short plant size in [[petunia]]. Furthermore, there are large differences in the efficacy of paclobutrazol and uniconazole. For the plant species impatiens, salvia and marigold, 10 mg/L [[uniconazole]] are needed in order to generate the same plant size that is achieved by a concentration of 160 mg/L paclobutrazol. For the plant species petunia, 10 mg/L uniconazole are needed in order to generate the same plant size that is achieved by a [[concentration]] of 40 mg/L paclobutrazol. To this day, the cause of the dissimilarity in efficacy of the two chemicals is unknown. The single different characteristic between the two chemicals is the midpoint of the [[molecule]]s. In uniconazole, there is a double bond in the middle and in paclobutrazol, there is a single bond.<ref name="auto2"/>
===Turf management===

PBZ has been extensively used as a means to improve the quality of turf on golf courses, where it reduces the need for mowing and by increasing chlorophyll content has the effect of greening the grass.<ref>{{cite journal |doi=10.21273/HORTSCI.40.1.224 |doi-access=free|title=Physiological Response of ''TifEagle'' Bermudagrass to Paclobutrazol |year=2005 |last1=McCullough |first1=Patrick E. |last2=Liu |first2=Haibo |last3=McCarty |first3=Lambert B. |last4=Whitwell |first4=Ted |journal=Hortscience |volume=40 |pages=224–226 }}</ref><ref name=Baris>{{Cite journal|url=https://doi.org/10.1002/etc.185|title=A quantitative analysis of over twenty years of golf course monitoring studies|first1=Reuben D.|last1=Baris|first2=Stuart Z.|last2=Cohen|first3=N. LaJan|last3=Barnes|first4=Juleen|last4=Lam|first5=Qingli|last5=Ma|date=March 28, 2010|journal=Environmental Toxicology and Chemistry|volume=29|issue=6|pages=1224–1236|doi=10.1002/etc.185|doi-access=free|pmid=20821564|s2cid=11874015}}</ref>
== Side effects ==
===Cereal crops===
Paclobutrazol can have multiple side effects on different kinds of levels. On a cellular level, paclobutrazol is capable to inhibit the growth of [[bacteria]]. Thereby, it is not important how high the concentration of the compound is.
By diverting the plant's productivity from stem elongation into seed production, PBZ can increase grain yields and reduce potential for [[lodging (agriculture)|lodging]].<ref name=Wakjira/><ref>{{cite journal | last1=Kamran | first1=Muhammad | last2=Cui | first2=Wenwen | last3=Ahmad | first3=Irshad | last4=Meng | first4=Xiangping | last5=Zhang | first5=Xudong | last6=Su | first6=Wennan | last7=Chen | first7=Junzhi | last8=Ahmad | first8=Shakeel | last9=Fahad | first9=Shah | last10=Han | first10=Qingfang | last11=Liu | first11=Tiening | title=Effect of paclobutrazol, a potential growth regulator on stalk mechanical strength, lignin accumulation and its relation with lodging resistance of maize | journal=[[Plant Growth Regulation]] | publisher=[[Springer Science+Business Media|Springer]] | volume=84 | issue=2 | date=2017-11-08 | issn=0167-6903 | doi=10.1007/s10725-017-0342-8 | pages=317–332| s2cid=52322462 }}</ref><ref>{{Cite journal |title=Growth, Photosynthetic Efficiency, Rate of Transpiration, Lodging, and Grain Yield of Tef (''Eragrostis Tef (Zucc) Trotter'') as Influenced by Stage and Rate of Paclobutrazol Application |first=T.|last=Tekalign|date=December 7, 2007|journal=East African Journal of Sciences|volume=1|issue=1|pages=35–44|doi=10.4314/eajsci.v1i1.40339 |doi-access=free}}</ref> The same mechanism is responsible for modern high-yield semi-dwarf crops such as the [[IR8|IR8 rice variety]].<ref>{{cite web |url=https://strasa.irri.org/ |title=Stress Tolerant Rice |publisher=International Rice Research Institute |access-date=2022-04-07 |website=strasa.irri.org}}</ref>

However, it also has an effect on the cell morphology of plants. The study analyzing ''[[Ophiopogon japonicus]]'' presented that paclobutrazol is capable of thickening the cell walls. Thereby, the cell becomes tinier and the arrangement of cells is more dense. The cells can lose their organelles and can get separated due to the thickened cell walls.

However, there are also changes on a molecular level. A study that analyzed the effects of paclobutrazol on ''Ophiopogon japonicus'' showed that a paclobutrazol concentration of 3 g/L is able to increase the amount of [[Saponin|saponins]]. Moreover, a paclobutrazol concentration of 2.8 g/L is able to increase the amount of [[flavonoid]]s.<ref name="auto1">{{Cite journal|title=Effect of Paclobutrazol on the Physiology and Biochemistry of Ophiopogon japonicus|first1=Zezhou|last1=Zhang|first2=Ruixing|last2=Li|first3=Deyong|last3=Chen|first4=Jieyin|last4=Chen|first5=Ouli|last5=Xiao|first6=Zhiqiang|last6=Kong|first7=Xiaofeng|last7=Dai|date=August 28, 2021|journal=Agronomy|volume=11|issue=8|pages=1533|doi=10.3390/agronomy11081533|doi-access=free}}</ref>


== Effects on the environment ==
== Effects on the environment ==
PBZ has been the subject of extensive [[Regulation of pesticides in the European Union|regulatory studies]], including in the European Union<ref name=EFSA>
Along with the desired effect of paclobutrazol as a plant growth inhibitor and [[fungicide]], it has some effects on the environment.
{{cite journal |doi=10.2903/j.efsa.2010.1876 |doi-access=free |title=Conclusion on the peer review of the pesticide risk assessment of the active substance paclobutrazol |journal=EFSA Journal |year=2010 |volume=8 |issue=11 |page=1876 }}</ref> and the US.<ref name=MDAR/> These data have been summarised.<ref name=PPDB/> It was assessed as being of moderate acute toxicity, mildly irritating to skin and eyes and unlikely to be genotoxic or carcinogenic to humans.<ref name=EFSA/> PBZ is relatively stable in water and soil. Under laboratory [[Aerobic organism|aerobic]] or [[Anaerobic organism|anaerobic]] conditions, the [[half-life]] of paclobutrazol can be higher than one year.<ref name=EFSA/> However, in a 2010 [[Quantitative analysis (chemistry)|quantitative analysis]], PBZ was detected in only 3 out of 440 groundwater samples from golf turf areas with a maximum concentration of 4.2 [[Microgram|µg]]/L.<ref name=Baris/> In Europe, the highest tolerable concentration of paclobutrazol in drinking water is 66 µg/L.<ref name=MDAR/>

Paclobutrazol is considered to be a stable compound in the water and soil. Under [[Aerobic organism|aerobic]] or [[Anaerobic organism|anaerobic]] conditions, the [[half-life]] of paclobutrazol is higher than one year. The potential of paclobutrazol for passing{{clarify|date=March 2022}} soil and water is regarded as moderate. When the soil has a higher amount of [[organic matter]] and the [[pH]] of the soil becomes low, the [[adsorption]] seems to increase. Experiments with [[methane]]-labeled paclobutrazol showed that the compound has a low mobility in soils like sand and clay-[[loam]]. Experiments with [[triazole]]-labeled paclobutrazol showed that the compound has a low mobility in sand and in sandy loam. Most of the compound (ca. 59 – 91%) did not get deeper than {{convert|10|cm|frac=2}} into the soil. Different studies showed that residues and degradates of paclobutrazol can be found at maximum 10% of the used soils with a maximum depth of {{convert|48|in|cm}}. Due to this reason, it is not very likely for the [[degradation|degradate]]{{dn|date=March 2022}} compounds to reach the [[groundwater]].<ref name="auto">{{cite web|title=Active Ingredient Paclobutrazol: Review Conducted by MDAR and MassDEP for Use in Sensitive Areas of Rights-of-Way in Massachusetts.|date=January 2012|url=https://www.mass.gov/doc/paclobutrazol-review-jan-2012pdf/download?_ga=2.169004968.820722649.1646429016-1603828005.1646429016|accessdate=4 February 2022}}</ref> In a 2010 study, paclobutrazol was detected in 3 out of 440 groundwater samples from golf turf areas with a maximum concentration of 4.2 [[Microgram|µg]]/L, in one [[Quantitative analysis (chemistry)|quantitative analysis]]. <ref>{{Cite journal|url=https://doi.org/10.1002/etc.185|title=A quantitative analysis of over twenty years of golf course monitoring studies|first1=Reuben D.|last1=Baris|first2=Stuart Z.|last2=Cohen|first3=N. LaJan|last3=Barnes|first4=Juleen|last4=Lam|first5=Qingli|last5=Ma|date=March 28, 2010|journal=Environmental Toxicology and Chemistry|volume=29|issue=6|pages=1224–1236|doi=10.1002/etc.185|pmid=20821564|s2cid=11874015}}</ref> In Europe, the highest tolerable concentration of paclobutrazol in drinking water is 66 µg/L.<ref name="auto"/>

=== Effects on plants ===
As a [[Chemical synthesis|synthetic]] chemical, paclobutrazol is typically applied as a plant growth regulator with the purpose of enhancing the production and quality of crops.<ref name="auto3">{{Cite journal|url=https://doi.org/10.1080/23311932.2018.1525169|title=A review on: Response of crops to paclobutrazol application|first=Wakjira|last=Tesfahun|editor-first=Fatih|editor-last=Yildiz|date=January 1, 2018|journal=Cogent Food & Agriculture|volume=4|issue=1|pages=1525169|via=Taylor and Francis+NEJM|doi=10.1080/23311932.2018.1525169|s2cid=134517280}}</ref> Paclobutrazol is used to increase the weight and amount of fruits from a tree. The quality of the fruits are refined by elevated amounts of [[carbohydrate]]s, [[total soluble solids]] (TSS), the TSS/[[titratable acid]]ity ratio (TSS/TA ratio) and a decreased acidity.<ref>{{Cite journal|url=https://doi.org/10.1186/s40538-020-00199-z|title=Paclobutrazol as a plant growth regulator|first1=Bizuayehu|last1=Desta|first2=Getachew|last2=Amare|date=January 7, 2021|journal=Chemical and Biological Technologies in Agriculture|volume=8|issue=1|pages=1|via=BioMed Central|doi=10.1186/s40538-020-00199-z|s2cid=230796693}}</ref> Paclobutrazol stimulates the [[Anatomical terms of location#Elongated organisms|elongation]] of roots and the stem diameter growth, as well as maintains the number of the leaves and suppresses the increase in the height of plants.<ref name="auto3"/><ref name="auto1"/><ref>{{Cite journal|title=Paclobutrazol induces tolerance in tomato to deficit irrigation through diversified effects on plant morphology, physiology and metabolism|first1=Sikander|last1=Pal|first2=Jiangsan|last2=Zhao|first3=Asif|last3=Khan|first4=Narendra Singh|last4=Yadav|first5=Albert|last5=Batushansky|first6=Simon|last6=Barak|first7=Boris|last7=Rewald|first8=Aaron|last8=Fait|first9=Naftali|last9=Lazarovitch|first10=Shimon|last10=Rachmilevitch|date=December 22, 2016|journal=Scientific Reports|volume=6|issue=1|pages=39321|doi=10.1038/srep39321|pmid=28004823|pmc=5177942|bibcode=2016NatSR...639321P}}</ref> Paclobutrazol can change the [[Morphology (biology)|morphology]] of leaves. Leaves can become thicker and the [[stoma]]ta of the leaves can become smaller. The root density can also be greater which increases an environmental stress tolerance and a resistance against diseases.<ref name="auto"/> Peng ''et al.'', 2014 produce better [[lodging (agriculture)|lodging]] tolerance using paclobutrazol.<ref name="Liu-et-al-2018">{{cite journal | last1=Liu | first1=Qingquan | last2=Luo | first2=Le | last3=Zheng | first3=Luqing | title=Lignins: Biosynthesis and Biological Functions in Plants | journal=[[International Journal of Molecular Sciences]] | publisher=[[MDPI]] | volume=19 | issue=2 | date=2018-01-24 | issn=1422-0067 | doi=10.3390/ijms19020335 | page=335 | pmid=29364145 | pmc=5855557 | s2cid=1117174| doi-access=free }}<!--- Published by MDPI but well cited including by Vaahtera et al., 2019... ---></ref> They find that [[winter wheat]] undergoes reduction of [[internode (botany)|internode]] length, thickened internodes, increased [[lateral (anatomy)|lateral]] growth, increased [[lignin]] synthesis [[enzyme]] activity and therefore increased lignification with application of this compound.<ref name="Liu-et-al-2018" /> Although this does not reduce lodging it does make lodging less harmful.<ref name="Liu-et-al-2018" />

It is believed that paclobutrazol is able to change [[Hormone|hormonal]] processes. Paclobutrazol is capable of inhibiting the production of [[gibberellin]] by hindering the production of ent-kaurene. As a consequence, less gibberellin will be made active, impeding [[Plant stem|stem]] elongation.<ref name="auto3"/> Normally, gibberellin initiates cell elongation. However, if less gibberellin is produced, cells can divide but not elongate.<ref name="auto"/>

Paclobutrazol also regulates plant growth by changing the [[Photosynthesis|photosynthetic]] rate. Paclobutrazol lowers plant growth of rice plants, makes rice seedlings distribute a smaller amount of [[Photosynthate partitioning|photosynthates]] during vegetative growth, and distribute a higher amount of photosynthates during the development of seeds. Elevated concentrations of paclobutrazol can also lead to [[dwarfism]] of the plant.<ref>{{Cite journal|url=https://journal.biotrop.org/index.php/biotropia/article/view/478|title=EFFECTS OF BLUE LIGHT AND PACLOBUTRAZOL ON SEED GERMINATION, VEGETATIVE GROWTH AND YIELD OF BLACK RICE (Oryza sativa L. ‘Cempo Ireng’)|first1=Kumala|last1=Dewi|first2=Rizkika Zakka|last2=Agustina|first3=Farida|last3=Nurmalika|date=March 28, 2016|journal=BIOTROPIA - the Southeast Asian Journal of Tropical Biology|volume=23|issue=2|pages=85–96|via=journal.biotrop.org|doi=10.11598/btb.2016.23.2.478|s2cid=55755782}}</ref> In addition, paclobutrazol raises the amount of [[chlorophyll]] in plants.<ref>{{Cite journal|url=https://doi.org/10.1186/1756-0500-5-137|title=Paclobutrazol treatment as a potential strategy for higher seed and oil yield in field-grown camelina sativa L. Crantz|first1=Sumit|last1=Kumar|first2=Sreenivas|last2=Ghatty|first3=Jella|last3=Satyanarayana|first4=Anirban|last4=Guha|first5=BSK|last5=Chaitanya|first6=Attipalli R.|last6=Reddy|date=March 13, 2012|journal=BMC Research Notes|volume=5|issue=1|pages=137|via=BioMed Central|doi=10.1186/1756-0500-5-137|pmid=22410213|pmc=3320555}}</ref><ref>{{Cite journal|url=https://www.ajol.info/index.php/eajsci/article/view/40339|title=Growth, Photosynthetic Efficiency, Rate of Transpiration, Lodging, and Grain Yield of Tef (Eragrostis Tef (Zucc) Trotter) as Influenced by Stage and Rate of Paclobutrazol Application|first=T.|last=Tekalign|date=December 7, 2007|journal=East African Journal of Sciences|volume=1|issue=1|pages=35–44|via=www.ajol.info|doi=10.4314/eajsci.v1i1.40339}}</ref> It is hypothesized that this is due to a reduced harm which arises through [[Reactive oxygen species|reactive oxygen]] and alterations in the amounts of [[Vitamin C|ascorbate]], [[ascorbate peroxidase]] and [[carotenoid]]s.<ref name="auto3"/> Besides, [[cytokinin]] is increasingly produced during the application of paclobutrazol. [[Cytokinin]] is able to improve the differentiation of [[chloroplast]]s and the production of [[chlorophyll]], and it inhibits the degradation of chlorophyll.<ref>Nivedithadevi, D.; Somasundaram, R.; Pannerselvam, R.;[https://www.ijddr.in/drug-development/effect-of-abscisic-acid-paclobutrazol-and-salicylic-acid-on-the-growthand-pigment-variation-in-solanum-trilobatum-l.php?aid=5079 Effect of abscisic acid, paclobutrazol and salicylic acid on the growth and pigment variation in solanum trilobatum (I).] International Journal Drug Developments Researcher. 2012. 4(3):236–246</ref>

Environmental [[stressor]]s such as increased temperature, [[drought]], coldness or [[Ultraviolet|UV radiation]] can harm the yield.<ref>{{Cite journal|url=http://doi.org/10.36632/mejar/2020.9.4.66|title=Protective Role of Spermidine on two Tomato Cultivars against Cold-Induced Lipid Peroxidation by Enhancing Capacity of Anti-Oxidative System|date=March 28, 2020|journal=Middle East Journal of Agriculture Research|doi=10.36632/mejar/2020.9.4.66|s2cid=242482155}}</ref> Since paclobutrazol can make crops more tolerant against droughts, it is applied to the plants to prevent yield loss. The exact mechanism of how paclobutrazol does this is unknown. However, it is believed that [[antioxidant]] enzymes and the amount of free [[proline]] play a role.<ref name="auto3"/> Some scientists hypothesize that antioxidant enzymes , which are stimulated by paclobutrazol, secure the photosynthesis from getting destroyed by stress-induced reactive oxygen species.<ref>{{Cite journal|title=Effects of water-deficit stress and paclobutrazol on growth, relative water content, electrolyte leakage, proline content and some antioxidant changes in ''Curcuma alismatifolia'' Gagnep. cv. Chiang Mai Pink|first1=Jarunee|last1=Jungklang|first2=Kobkiat|last2=Saengnil|first3=Jamnong|last3=Uthaibutra|date=November 1, 2017|journal=Saudi Journal of Biological Sciences|volume=24|issue=7|pages=1505–1512|doi=10.1016/j.sjbs.2015.09.017|pmid=30294219|pmc=6169545}}</ref>

Paclobutrazol is applied to different kinds of plants. ''[[Ophiopogon japonicus]]'' is one of them. ''Ophiopogon japonicus'' is a [[tuber]] root that is harvested and applied as medication. ''Ophiopogon japonicus'' contains [[Saponin|saponins]] and [[Flavonoid|flavonoids]] which are of importance because of their pharmacological reactions. Paclobutrazol is utilized with the purpose of increasing the production of the plant. The effects of paclobutrazol  on ''Ophiopogon japonicus''  (e.g. stimulation of the elongation of roots and suppression of the height of plants) can differ depending on the paclobutrazol concentration.<ref name="auto1"/> According to a study,<ref name="auto1"/> the influence on the plant ''Ophiopogon japonicus'' became significantly smaller as the paclobutrazol concentration reaches a level of 22.5 g/L. Additionally, saponins stopped accumulating at a paclobutrazol concentration of 11.3 g/L and 22.5 g/L. Regardless of the paclobutrazol concentration, paclobutrazol has a [[Bacteriostatic agent|bacteriostatic]] effect.<ref name="auto1"/> In ''[[Stevia]]'' spp., Hajihashemi ''et al.'', 2013 it was found that Paclobutrazol inhbits [[gene transcription|transcription]] of [[steviol]] [[glycoside]] synthesis [[gene]]s.<ref name="Zhou-et-al-2021">{{cite journal | last1=Zhou | first1=Xuan | last2=Gong | first2=Mengyue | last3=Lv | first3=Xueqin | last4=Liu | first4=Yanfeng | last5=Li | first5=Jianghua | last6=Du | first6=Guocheng | last7=Liu | first7=Long | title=Metabolic engineering for the synthesis of steviol glycosides: current status and future prospects | journal=[[Applied Microbiology and Biotechnology]] | publisher=[[Springer Science+Business Media|Springer]] | volume=105 | issue=13 | year=2021 | issn=0175-7598 | doi=10.1007/s00253-021-11419-3 | pages=5367–5381| pmid=34196745 | s2cid=235698103 }}</ref><ref name="Hajihashemi-2021">{{cite book | last=Hajihashemi | first=Shokoofeh | title=Steviol Glycosides | chapter=Agronomic practices | publisher=[[Elsevier]] | year=2021 | doi=10.1016/b978-0-12-820060-5.00002-9 | pages=31–56| isbn=9780128200605 | s2cid=241825889 }}</ref> This is believed to reduce [[steviol]] content in the final plant product.<ref name="Zhou-et-al-2021" /><ref name="Hajihashemi-2021" />

==== Resistance ====
The ''[[Arabidopsis thaliana|Arabidopsis]]'' allele ''[[gai-t6]]'' (of the [[giberellic acid interacting]] gene) confers [[herbicide resistance|resistance]] to paclobutrazol's damage to [[vegetative growth]].<ref name="Tanaka-et-al-2007">{{cite journal | last1=Ueguchi-Tanaka | first1=Miyako | last2=Nakajima | first2=Masatoshi | last3=Motoyuki | first3=Ashikari | last4=Matsuoka | first4=Makoto | title=Gibberellin Receptor and Its Role in Gibberellin Signaling in Plants | journal=[[Annual Review of Plant Biology]] | publisher=[[Annual Reviews (publisher)|Annual Reviews]] | volume=58 | issue=1 | date=2007-06-01 | issn=1543-5008 | doi=10.1146/annurev.arplant.58.032806.103830 | pages=183–198| pmid=17472566 }}</ref>


=== Effects on fungi ===
== Resistance ==
Paclobutrazol exerts a [[fungistatic]] effect.<ref name="Jeger-2004">{{cite journal | last=Jeger | first=M.J. | title=Analysis Of Disease Progress As A Basis For Evaluating Disease Management Practices | journal=[[Annual Review of Phytopathology]] | publisher=[[Annual Reviews (publisher)|Annual Reviews]] | volume=42 | issue=1 | date=2004-09-01 | issn=0066-4286 | doi=10.1146/annurev.phyto.42.040803.140427 | pages=61–82| pmid=15283660 }}</ref> Burpee ''et al.'', 1996 find significantly reduces both incidence and severity of [[dollar spot]] on [[creeping bentgrass]].<ref name="Jeger-2004" />
The ''[[Arabidopsis thaliana|Arabidopsis]]'' allele ''[[gai-t6]]'' (of the [[giberellic acid interacting]] gene) confers [[herbicide resistance|resistance]] to paclobutrazol's damage to [[vegetative growth]]. However, in normal use, there is no selective pressure on plants to develop resistance to PBZ since it is not lethal to them.<ref name="Tanaka-et-al-2007">{{cite journal | last1=Ueguchi-Tanaka | first1=Miyako | last2=Nakajima | first2=Masatoshi | last3=Motoyuki | first3=Ashikari | last4=Matsuoka | first4=Makoto | title=Gibberellin Receptor and Its Role in Gibberellin Signaling in Plants | journal=[[Annual Review of Plant Biology]] | publisher=[[Annual Reviews (publisher)|Annual Reviews]] | volume=58 | issue=1 | date=2007-06-01 | issn=1543-5008 | doi=10.1146/annurev.arplant.58.032806.103830 | pages=183–198| pmid=17472566 }}</ref>


== References ==
== References ==
{{reflist|liststyle=decimal}}
{{reflist}}
==External links ==
==External links ==
* {{PPDB|504}}
* {{PPDB|504}}

Revision as of 13:23, 7 April 2022

Paclobutrazol
Names
IUPAC name
(2RS,3RS)-1-(4-Chlorophenyl)-4,4-dimethyl-2-(1H-1,2,4-triazol-1-yl)-3-pentanol
Other names
PP333
Identifiers
3D model (JSmol)
Abbreviations PBZ
ChEBI
ChemSpider
ECHA InfoCard 100.121.374 Edit this at Wikidata
UNII
  • InChI=1S/C15H20ClN3O/c1-15(2,3)14(20)13(19-10-17-9-18-19)8-11-4-6-12(16)7-5-11/h4-7,9-10,13-14,20H,8H2,1-3H3/t13-,14+/m0/s1
    Key: RMOGWMIKYWRTKW-UONOGXRCSA-N
  • PBZ: InChI=1/C15H20ClN3O/c1-15(2,3)14(20)13(19-10-17-9-18-19)8-11-4-6-12(16)7-5-11/h4-7,9-10,13-14,20H,8H2,1-3H3/t13-,14+/m0/s1
    Key: RMOGWMIKYWRTKW-DUXBJXIBNA-N
  • (2R,3R) isomer: Key: RMOGWMIKYWRTKW-KGLIPLIRSA-N
  • (2S,3S) isomer: Key: RMOGWMIKYWRTKW-UONOGXRCSA-N
  • PBZ: CC(C)(C)[C@@H]([C@H](CC1=CC=C(C=C1)Cl)N2C=NC=N2)O
Properties[1]
C15H20ClN3O
Molar mass 293.80 g·mol−1
Appearance White crystalline solid
Density 1.23 g/cm3
Melting point 165-166℃
Boiling point 460.9 °C (861.6 °F; 734.0 K) at 760 mHg
22.9 mg/L (20 °C)
log P 3.11
Hazards
Occupational safety and health (OHS/OSH):
Main hazards
 Xn
Flash point 232.6 °C (450.7 °F; 505.8 K)
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).

Paclobutrazol (PBZ) is the ISO common name for an organic compound that is used as a a plant growth retardant and triazole fungicide.[2][3] It is a known antagonist of the plant hormone gibberellin, acting by inhibiting gibberellin biosynthesis, reducing internodal growth to give stouter stems, increasing root growth, causing early fruitset and increasing seedset in plants such as tomato and pepper. PBZ has also been shown to reduce frost sensitivity in plants. Moreover, paclobutrazol can be used as a chemical approach for reducing the risk of lodging in cereal crops. PBZ has been used by arborists to reduce shoot growth and shown to have additional positive effects on trees and shrubs. Among those are improved resistance to drought stress, darker green leaves, higher resistance against fungi and bacteria, and enhanced development of roots. Cambial growth, as well as shoot growth, has been shown to be reduced in some tree species.

Structure and synthesis

The first synthesis of paclobutrazol was disclosed in patents filed by an ICI group working at Jealott's Hill.[4]

4-Chlorobenzaldehyde and pinacolone are combined in an aldol condensation to form a chalcone which is hydrogenated using Raney nickel as catalyst to give a substituted ketone. This material is brominated and the resulting compound treated with the sodium salt of 1,2,4-triazole in a nucleophilic substitution reaction. The final reduction reaction uses sodium borohydride, which in cold methanol gives almost exclusively the diastereomer pair having the absolute configuration (2R,3R) and its enantiomer (2S,3S), with only about 2% of the alternative (2R,3S) and (2S,3R) isomers. However, this pair of isomers can be produced when the reduction is carried out using butylmagnesium bromide.[5]

In a 1984 study, ICI workers separated the individual enantiomers by chiral resolution and were able to demonstrate that only the (2R,3R) isomer displays substantial fungicidal activity, whereas the (2S,3S) isomer is responsible for the growth regulating properties. However, the commercial product (developed under the code number PP333) was the racemic material, since separation of the isomers was unnecessary when both components had utility in agriculture.[5]

Mechanism of action

Paclobutrazol is an inhibitor of enzymes which use cytochrome P450 as a co-factor. Their active site contains a heme center which activates oxygen from the air to oxidise their substrates. The (2S,3S) isomer inhibits the enzyme ent-kaurene oxidase[5][6] which is on the main biosynthetic pathway to gibberellins, which are important plant hormones.[7][8] A secondary effect arising from the inhibition of ent-kaurene oxidase is that its precursor, geranylgeranyl pyrophosphate accumulates in the plant and some of this is diverted into additional production of the phytol group of chlorophyll and the hormone abscisic acid. The latter is responsible for controlling transpiration of water through the leaves and hence PBZ treatment can lead to better tolerance of drought conditions.[9] The (2R,3R) isomer is a better fit to the active site of the fungal cytochrome P450 14α-demethylase. This inhibits the conversion of lanosterol to ergosterol, a component of the fungal cell membrane, which is lethal for many species.[5] Many other azole derivatives including propiconazole and tebuconazole show this type of activity, so the main commercial opportunity for paclobutrazol was as a plant growth retardant and it was first marketed by ICI in 1985 under the trade names Bonzi, Clipper, Cultar and Parlay.[1][10]

Usage

As an antagonist of gibberellin biosynthesis, PBZ has a growth retardant effect on most plant species.[9] It is absorbed by plant tissues and transported via the xylem to the growing parts, where the rate of cell division is reduced compared to untreated plants and the new cells do not elongate.[10][11]: 5 

Ornamental crops

PBZ is used in horticulture, especially for glasshouse-reared perennial plants.[12][13]

Trees and shrubs

The ability of PBZ to reduce the growth of trees and shrubs means that it has found use in areas where there is a need to moderate such growth, for example under electric power lines and where a right-of-way is to be maintained. A single application of the growth regulator can give season-long control.[11][14]

Fruit and vegetables

PBZ is used to increase the quantity and quality of orchard fruit and of vegetables. The quality is measured by elevated amounts of carbohydrates, total soluble solids (TSS), the TSS/titratable acidity ratio and a decreased acidity.[9] It stimulates the growth of roots and stems and maintains the number of the leaves but suppresses the height of the plants.[15][16][17]

Turf management

PBZ has been extensively used as a means to improve the quality of turf on golf courses, where it reduces the need for mowing and by increasing chlorophyll content has the effect of greening the grass.[18][19]

Cereal crops

By diverting the plant's productivity from stem elongation into seed production, PBZ can increase grain yields and reduce potential for lodging.[3][20][21] The same mechanism is responsible for modern high-yield semi-dwarf crops such as the IR8 rice variety.[22]

Effects on the environment

PBZ has been the subject of extensive regulatory studies, including in the European Union[23] and the US.[11] These data have been summarised.[1] It was assessed as being of moderate acute toxicity, mildly irritating to skin and eyes and unlikely to be genotoxic or carcinogenic to humans.[23] PBZ is relatively stable in water and soil. Under laboratory aerobic or anaerobic conditions, the half-life of paclobutrazol can be higher than one year.[23] However, in a 2010 quantitative analysis, PBZ was detected in only 3 out of 440 groundwater samples from golf turf areas with a maximum concentration of 4.2 µg/L.[19] In Europe, the highest tolerable concentration of paclobutrazol in drinking water is 66 µg/L.[11]

Resistance

The Arabidopsis allele gai-t6 (of the giberellic acid interacting gene) confers resistance to paclobutrazol's damage to vegetative growth. However, in normal use, there is no selective pressure on plants to develop resistance to PBZ since it is not lethal to them.[24]

References

  1. ^ a b c Pesticide Properties Database. "Paclobutrazol". University of Hertfordshire.
  2. ^ "Compendium of Pesticide Common Names: paclobutrazol". BCPC.
  3. ^ a b Tesfahun, Wakjira (January 1, 2018). Yildiz, Fatih (ed.). "A review on: Response of crops to paclobutrazol application". Cogent Food & Agriculture. 4 (1): 1–9. doi:10.1080/23311932.2018.1525169. S2CID 134517280.
  4. ^ GB patent 1595696, Boize, L.M.; Sugavanam, B. & Shephard, M.C. et al., "Triazoles and imidazoles useful as plant fungicides and growth regulating agents", issued 1981-08-12, assigned to ICI Ltd 
  5. ^ a b c d Sugavanam, Balasubramanyan (1984). "Diastereoisomers and enantiomers of paclobutrazol: Their preparation and biological activity". Pesticide Science. 15 (3): 296–302. doi:10.1002/ps.2780150312.
  6. ^ Davidson, Sandra E.; Smith, Jennifer J.; Helliwell, Chris A.; Poole, Andrew T.; Reid, James B. (2004). "The Pea Gene LH Encodes ent-Kaurene Oxidase". Plant Physiology. 134 (3): 1123–1134. doi:10.1104/pp.103.032706. PMC 389936. PMID 14988475.
  7. ^ Rademacher, Wilhelm (June 2000). "Growth Retardants: Effects on Gibberellin Biosynthesis and Other Metabolic Pathways". Annual Review of Plant Physiology and Plant Molecular Biology. 51 (1): 501–531. doi:10.1146/annurev.arplant.51.1.501. PMID 15012200.
  8. ^ Hedden, Peter (2020). "The Current Status of Research on Gibberellin Biosynthesis". Plant and Cell Physiology. 61 (11): 1832–1849. doi:10.1093/pcp/pcaa092. PMC 7758035. PMID 32652020.
  9. ^ a b c Desta, Bizuayehu; Amare, Getachew (January 7, 2021). "Paclobutrazol as a plant growth regulator". Chemical and Biological Technologies in Agriculture. 8 (1). doi:10.1186/s40538-020-00199-z. S2CID 230796693.
  10. ^ a b Worthing C.R., ed. (1987). The Pesticide Manual - A World Compendium (Eighth ed.). British Crop Protection Council. pp. 628–629. ISBN 0948404019.
  11. ^ a b c d "Active Ingredient Paclobutrazol: Review Conducted by MDAR and MassDEP for Use in Sensitive Areas of Rights-of-Way in Massachusetts". January 2012. Retrieved 4 February 2022.
  12. ^ Whipker, Brian E. (2022). "Wide Assortment of Available PGRs" (PDF). GrowerTalks. Ball Publishing. pp. 10–12. Retrieved 2022-04-06.
  13. ^ Latimer, Joyce G. (2022). "Growth Regulators for Containerized Herbaceous Perennial Plants" (PDF). GrowerTalks. Ball Publishing. pp. 14–60. Retrieved 2022-04-06.
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