Pollen tube: Difference between revisions

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<ref name="Geitmann2007">{{cite journal|last=Geitmann|first=Anja|coauthors=Palanivelu Ravishankar|title=Fertilization requires communication: Signal generation and perception during pollen tube guidance|journal=Floriculture and Ornamental Biotechnology|year=2007|volume=1|pages=77–89}}</ref>
<ref name="Geitmann2007">{{cite journal|last=Geitmann|first=Anja|coauthors=Palanivelu Ravishankar|title=Fertilization requires communication: Signal generation and perception during pollen tube guidance|journal=Floriculture and Ornamental Biotechnology|year=2007|volume=1|pages=77–89}}</ref>
.<ref name="Malho2006">{{cite book|last=Malhó|first=Rui|title=The pollen tube: a cellular and molecular perspective|year=2006|publisher=Springer}}</ref>
.<ref name="Malho2006">{{cite book|last=Malhó|first=Rui|title=The pollen tube: a cellular and molecular perspective|year=2006|publisher=Springer}}</ref>
<ref name="Gossot2007">{{cite journal|last=Gossot|first=Olivier|coauthors=Geitmann Anja|title=Pollen tube growth: coping with mechanical obstacles involves the cytoskeleton|journal=Planta|year=2007|volume=226|pages=405–416}}</ref>
<ref name="Gossot2007">{{cite journal|last=Gossot|first=Olivier|coauthors=Geitmann Anja|title=Pollen tube growth: coping with mechanical obstacles involves the cytoskeleton|journal=Planta|year=2007|volume=226|pages=405–416|doi=10.1007/s00425-007-0491-5|pmid=17318608|issue=2}}</ref>
<ref name="Messerli2000">{{cite journal|last=Messerli|first=Mark|coauthors=et al.|title=Periodic increases in elongation rate precede increases in cytosolic Ca2+ during pollen tube growth|journal=Developmental Biology|year=2000|volume=222|pages=84–98|pmid=10885748}}</ref>
<ref name="Messerli2000">{{cite journal|last=Messerli|first=Mark|coauthors=et al.|title=Periodic increases in elongation rate precede increases in cytosolic Ca2+ during pollen tube growth|journal=Developmental Biology|year=2000|volume=222|pages=84–98|pmid=10885748|doi=10.1006/dbio.2000.9709|issue=1}}</ref>
<ref name="Malho1998">{{cite journal|last=Malhó|first=Rui|title=Pollen tube guidance – the long and winding road|journal=Sexual Plant Reproduction|year=1998|volume=11|pages=242–244}}</ref>
<ref name="Malho1998">{{cite journal|last=Malhó|first=Rui|title=Pollen tube guidance – the long and winding road|journal=Sexual Plant Reproduction|year=1998|volume=11|pages=242–244|doi=10.1007/s004970050148|issue=5}}</ref>
<ref name="Okuda2010">{{cite journal|last=Okuda|first=Satohiro|coauthors=Higashiyama Tetsuya|title=Pollen tube guidance by attractant molecules: LUREs|journal=Cell Structure and Function|year=2010|volume=35|pages=45–52}}</ref>
<ref name="Okuda2010">{{cite journal|last=Okuda|first=Satohiro|coauthors=Higashiyama Tetsuya|title=Pollen tube guidance by attractant molecules: LUREs|journal=Cell Structure and Function|year=2010|volume=35|pages=45–52|doi=10.1247/csf.10003|pmid=20562497|issue=1}}</ref>
<ref name="Mascarenhas1964">{{cite journal|last=Mascarenhas|first=Joseph|coauthors=Machlis Leonard|title=Chemotropic response of the pollen of Antirrhinum majus to calcium|journal=Plant Physiology|year=1964|volume=39|pages=70–77}}</ref>
<ref name="Mascarenhas1964">{{cite journal|last=Mascarenhas|first=Joseph|coauthors=Machlis Leonard|title=Chemotropic response of the pollen of Antirrhinum majus to calcium|journal=Plant Physiology|year=1964|volume=39|pages=70–77|doi=10.1104/pp.39.1.70|pmid=16655882|issue=1|pmc=550029}}</ref>
<ref name="Robinson1985">{{cite journal|last=Robinson|first=Kenneth|title=The Responses of Cells to Electrical Fields: A Review|journal=The Journal of Cell Biology|year=1985|volume=101}}</ref>
<ref name="Robinson1985">{{cite journal|last=Robinson|first=Kenneth|title=The Responses of Cells to Electrical Fields: A Review|journal=The Journal of Cell Biology|year=1985|volume=101}}</ref>
<ref name="Chebli2007">{{cite journal|last=Chebli|first=Youssef|coauthors=Geitmann Anja|title=Mechanical principles governing pollen tube growth|journal=Functional Plant Science and Biotechnology|year=2007|volume=1|pages=232–245}}</ref>
<ref name="Chebli2007">{{cite journal|last=Chebli|first=Youssef|coauthors=Geitmann Anja|title=Mechanical principles governing pollen tube growth|journal=Functional Plant Science and Biotechnology|year=2007|volume=1|pages=232–245}}</ref>

Revision as of 22:03, 3 October 2011

Pollen tubes growing from Lily pollen grains.

The pollen tubes is the male gametophyte of seed plants that acts as a conduit to transport the male sperm cells from the pollen grain, either from the stigma (in flowering plants or angiosperms) to the ovules at the base of the pistil, or directly through ovule tissue in some gymnosperms (conifers and gnetophytes).

After pollination, the pollen tube germinates from the pollen grain and grows the entire length through the stigma, style, ovary and ovules to reach the egg cell. In maize, this single cell can grow longer than 12 inches to traverse the length of the pistil. The sperm cells are not motile, so they are carried within the tube. As the tip of the tube reaches the egg cell, it bursts and releases two sperm cells leading to a double fertilization.

Pollen tubes were first discovered by Pierre Jean François Turpin.

The pollen tube journey

Angiosperm life cycle.

Seed plants reproduction is a complex process that includes several steps that may vary among species.[1] Each step is a vast procedure in his own right, but in general, the reproduction cycle of angiosperms starts with the production of pollen by the stamen, the male reproductive organ. Each pollen grain contains a vegetative cell, and a generative cell that divides to form two sperm cells: the male gametes. The pollen is delivered by the opening of anthers for subsequent pollination, that is, for the transfer of pollen grains to the pistil, the female reproductive organ. Pollination is usually carried out by wind, water or insects. The ovaries, on the other hand, hold the ovules that produce the female gamete: the egg cell, which waits in place for fertilisation.

Once a pollen grain settles on a compatible pistil, it germinates in response to a sugary fluid secreted by the mature stigma. Lipids at the surface of the stigma stimulate pollen tube growth for compatible pollen. Plants that are self-sterile inhibit the pollen grains from their own flowers from growing pollen tubes. The presence of multiple grains of pollen has been observed to stimulate quicker pollen tube growth in some plants. The vegetative cell then produces the pollen tube, a tubular protrusion from the pollen grain, which carries the sperm cells within its cytoplasm. This tube is the transportation medium of the male gamete to reach the egg cell.

The germinated pollen tube must then drill its way through the nutrient-rich style and curl to the bottom of the ovary to reach the ovule. Once the pollen tube successfully attains an ovule, it delivers the two sperm cells with a burst. One of them fertilizes the female gamete (the egg cell) to form an embryo, which will become the future plant. And the other one fuses with both polar nuclei of the central cell to form the endosperm, which serves as the embryo's food supply. The endosperm is rich in starch, proteins and oils and is a major source of human food (e.g., wheat, barley, rye, oats, corn). Finally, the ovary will develop into a fruit and the ovules will develop into seeds.

Pollen tubes: an excellent model

Cell biology is fundamental to all life sciences. Advancement in knowledge of cell physiology enables the improvement of life quality and the development of methodologies for prevention or treatment of many disorders and diseases in areas such as medicine, agriculture, among others. Pollen tubes are an excellent model for the understanding of plant cell behavior.[2] They are easily cultivated in vitro and have a very dynamic cytoskeleton that polymerizes at very high rates, providing the pollen tube with interesting mechanical properties.[3] For instance, the pollen tube has an unusual kind of growth; it extends exclusively at its apex. Extending the cell wall only at the tip minimizes friction between the tube and the invaded tissue. This tip growth is actually performed in a pulsating manner rather than in a steady fashion.[4] Remarkably, the pollen tube’s journey through the style often results in depth-to-diameter ratios above 100:1 and up to 1000:1 in certain species, whereas classic mechanical drilling is often only effective up to 15:1 ratios. However, the internal machinery and the external interactions that govern the dynamics of pollen tube growth are far from being fully understood.

Pollen tube guidance

Extensive work has been dedicated to comprehend how the pollen tube responds to extracellular guidance signals to achieve fertilization.[1][2][5][6] It is believed that pollen tubes react to a combination of chemical, electrical, and mechanical cues during its journey through the pistil.[7][8][9] However, it is not clear how these external cues work or how they are processed internally. Moreover, sensory receptors for any external cue have not been identified yet. Nevertheless, several aspects have already been identified as central in the process of pollen tube growth. The actin filaments in the cytoskeleton, the peculiar cell wall, secretory vesicle dynamics, and the flux of ions, to name a few, are some of the fundamental features readily identified as crucial, but whose role has not yet been completely elucidated.

Pollen tubes, as most biological systems, are influenced by electrical stimulus. Efforts have already been made to clarify the mechanisms of intra- and extracellular electrical signaling in pollen tubes. However, our understanding of how pollen tubes react to electric fields and how the electric cue is related to the internal dynamics of pollen tube growth remains limited. For instance, pollen tubes have been reported to grow towards the negative electrode,[10] positive electrode,[11] and nearest electrode[12] under constant electric fields. Another report states that pollen tubes do not change growth direction under AC electric fields.[13] Although it is believed that the behavior under electric fields may depend on the species, it is not clear how electric fields influence pollen tube growth.

See also

References

  1. ^ a b Geitmann, Anja (2007). "Fertilization requires communication: Signal generation and perception during pollen tube guidance". Floriculture and Ornamental Biotechnology. 1: 77–89. {{cite journal}}: Unknown parameter |coauthors= ignored (|author= suggested) (help)
  2. ^ a b Malhó, Rui (2006). The pollen tube: a cellular and molecular perspective. Springer.
  3. ^ Gossot, Olivier (2007). "Pollen tube growth: coping with mechanical obstacles involves the cytoskeleton". Planta. 226 (2): 405–416. doi:10.1007/s00425-007-0491-5. PMID 17318608. {{cite journal}}: Unknown parameter |coauthors= ignored (|author= suggested) (help)
  4. ^ Messerli, Mark (2000). "Periodic increases in elongation rate precede increases in cytosolic Ca2+ during pollen tube growth". Developmental Biology. 222 (1): 84–98. doi:10.1006/dbio.2000.9709. PMID 10885748. {{cite journal}}: Unknown parameter |coauthors= ignored (|author= suggested) (help)
  5. ^ Malhó, Rui (1998). "Pollen tube guidance – the long and winding road". Sexual Plant Reproduction. 11 (5): 242–244. doi:10.1007/s004970050148.
  6. ^ Okuda, Satohiro (2010). "Pollen tube guidance by attractant molecules: LUREs". Cell Structure and Function. 35 (1): 45–52. doi:10.1247/csf.10003. PMID 20562497. {{cite journal}}: Unknown parameter |coauthors= ignored (|author= suggested) (help)
  7. ^ Mascarenhas, Joseph (1964). "Chemotropic response of the pollen of Antirrhinum majus to calcium". Plant Physiology. 39 (1): 70–77. doi:10.1104/pp.39.1.70. PMC 550029. PMID 16655882. {{cite journal}}: Unknown parameter |coauthors= ignored (|author= suggested) (help)
  8. ^ Robinson, Kenneth (1985). "The Responses of Cells to Electrical Fields: A Review". The Journal of Cell Biology. 101.
  9. ^ Chebli, Youssef (2007). "Mechanical principles governing pollen tube growth". Functional Plant Science and Biotechnology. 1: 232–245. {{cite journal}}: Unknown parameter |coauthors= ignored (|author= suggested) (help)
  10. ^ Nakamura, N. (1991). "Electrotropism of pollen tubes o f c amellia and other plants". Sexual Plant Reproduction. 4: 138–143. {{cite journal}}: Unknown parameter |coauthors= ignored (|author= suggested) (help)
  11. ^ Wang, Chang (1989). "The response of pollen to applied electrical fields". Developmental Biology. 136 (2): 405–401. doi:10.1016/0012-1606(89)90266-2. PMID 2583370. {{cite journal}}: Unknown parameter |coauthors= ignored (|author= suggested) (help)
  12. ^ Malhó, Rui (1992). "Effect of electrical fields and external ionic currents on pollen-tube orientation". Sexual Plant Reproduction. 5: 57–63. doi:10.1007/BF00714558. {{cite journal}}: Unknown parameter |coauthors= ignored (|author= suggested) (help)
  13. ^ Platzer, Kristjan (1997). "AC fields of low frequency and amplitude stimulate pollen tube growth possibly via stimulation of the plasma membrane proton pump". Bioelectrochemistry and Bioenergetics. 44: 95–102. doi:10.1016/S0302-4598(96)05164-1. {{cite journal}}: Unknown parameter |coauthors= ignored (|author= suggested) (help)

External links

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