Moisture stress

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Moisture stress occurs when the water in a plant's cells is reduced to less than normal levels. This can occur because of a lack of water in the plant's root zone, higher rates of transpiration than the rate of moisture uptake by the roots, for example, because of an inability to absorb water due to a high salt content in the soil water or loss of roots due to transplantation. Moisture stress is more strongly related to water potential than it is to water content.[1][2][3]

Moisture stress also has an effect on stomatal openings of a plant, mainly causing a closure in stomata as to reduce the amount of carbon dioxide assimilation.[4] Closing of the stomata also slows the rate of transpiration, which limits water loss and helps to prevent the wilting effects of moisture stress.[5] This closing can be trigged by the roots sensing dry soil and in response producing the hormone ABA which when transported up the xylem into the leaves will reduce stomatal conductance and wall extensibility of growing cells. This lowers the rates of transpiration, photosynthesis and leaf expansion. ABA also increases the loosening of growing root cell walls and in turn increases root growth in an effort to find water in the soil.[6]

Phenotypic response of plants to long-term water stress was measured in corn and showed that plants respond to water stress with both an increase in root growth both laterally and vertically. In all Droughted conditions the corn showed decrease in plant height and yield due to the decrease in water availability.[7]

Genes induced during water-stress conditions are thought to function not only in protecting cells from water deficit by the production of important metabolic proteins but also in the regulation of genes for signal transduction in the water-stress response. There are four pathways that have been described that show the plants genetic response to moisture stress; two are ABA dependent while two are ABA independent. They all affect gene expression that increases the plants water stress tolerance.[8]

The effects of moisture stress on photosynthesis can depend as much on the velocity and degree of photosynthetic recovery, as it depends on the degree and velocity of photosynthesis decline during water depletion. Plants that are subjected to mild stress can recover in 1–2 days however, plants subjected to severe water stress will only recover 40-60% of its maximum photosynthetic rates the day after re watering and may never reach maximum photosynthetic rates. The recovery from moisture stress starts with an increase in water content in leaves reopening the stomata then the synthesis of photosynthetic proteins.[9][10]

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References[edit]

  1. ^ Waring, R. H.; Cleary, B. D. (1967). "Plant Moisture Stress: Evaluation by Pressure Bomb". Science. 155 (3767): 1248. doi:10.1126/science.155.3767.1248. PMID 17847540. 
  2. ^ Chappelka, Arthur H.; Freer-Smith, Peter H. (1995). "ScienceDirect – Environmental Pollution : Predisposition of trees by air pollutants to low temperatures and moisture stress". Environmental Pollution. 87 (1): 105–117. doi:10.1016/S0269-7491(99)80013-X. PMID 15091613. 
  3. ^ Lee, J. A.; Stewart, G. R. (1 January 1971). "Desiccation Injury in Mosses. I. Intra-Specific Differences in the Effect of Moisture Stress on Photosynthesis". The New Phytologist. 70 (6): 1061–1068. JSTOR 2431023. 
  4. ^ Hand, JM; Young, E; Vasconcelos, AC (1982). "Leaf water potential, stomatal resistance, and photosynthetic response to water stress in peach seedlings". Plant Physiol. 69 (5): 1051–4. doi:10.1104/pp.69.5.1051. PMC 426357Freely accessible. PMID 16662343. 
  5. ^ Freeman, Scott (2014). Biological Science: Fifth Edition. USA: Pearson Education, Inc. p. 765. ISBN 978-0-321-74367-1. 
  6. ^ Lambers, Hans; Chapin II, F. Stuart; Pons, Thijs L. (2008). Plant physiological Ecology. New York, NY: Springer. p. 349. ISBN 978-0-387-78340-6.
  7. ^ Weaver, J.E. (1926) Root Development of Field Crops. McGraw Hill, New York.
  8. ^ Shinozaki, K., and K. Yamaguchi-Shinozaki. “Gene Expression and Signal Transduction in Water-Stress Response.” Plant Physiology 115.2 (1997): 327–334.
  9. ^ Chaves, M. M.; Flexas, J.; Pinheiro, C. (2009-02-01). "Photosynthesis under drought and salt stress: regulation mechanisms from whole plant to cell". Annals of Botany. 103 (4): 551–560. doi:10.1093/aob/mcn125. ISSN 0305-7364. PMC 2707345Freely accessible. PMID 18662937. 
  10. ^ Kirschbaum, M. U. F. (1988). "Recovery of photosynthesis from water stress in Eucalyptus pauciflora-a process in two stages". Plant, Cell and Environment. 11 (8): 685. doi:10.1111/j.1365-3040.1988.tb01151.x.