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Actin polymerization is essential for pollen tube growth.

ABSTRACT: Actin microfilaments, which are prominent in pollen tubes, have been implicated in the growth process; however, their mechanism of action is not well understood. In the present work we have used profilin and DNAse I injections, as well as latrunculin B and cytochalasin D treatments, under quantitatively controlled conditions, to perturb actin microfilament structure and assembly in an attempt to answer this question. We found that a approximately 50% increase in the total profilin pool was necessary to half-maximally inhibit pollen tube growth, whereas a approximately 100% increase was necessary for half-maximal inhibition of cytoplasmic streaming. DNAse I showed a similar inhibitory activity but with a threefold more pronounced effect on growth than streaming. Latrunculin B, at only 1--4 nM in the growth medium, has a similar proportion of inhibition of growth over streaming to that of profilin. The fact that tip growth is more sensitive than streaming to the inhibitory substances and that there is no correlation between streaming and growth rates suggests that tip growth requires actin assembly in a process independent of cytoplasmic streaming.

SUBMITTER: Vidali L

PROVIDER: S-EPMC58611 | biostudies-literature | 2001 Aug

REPOSITORIES: biostudies-literature

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Actin polymerization is essential for pollen tube growth.

Vidali L L McKenna S T ST Hepler P K PK

Molecular biology of the cell 20010801 8

Actin microfilaments, which are prominent in pollen tubes, have been implicated in the growth process; however, their mechanism of action is not well understood. In the present work we have used profilin and DNAse I injections, as well as latrunculin B and cytochalasin D treatments, under quantitatively controlled conditions, to perturb actin microfilament structure and assembly in an attempt to answer this question. We found that a approximately 50% increase in the total profilin pool was neces ...[more]

PMID: 11514633

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Project description:Background and aimsAn unusual form of pollen tube growth was observed for several Conospermum species (family Proteaceae). The rate of pollen tube growth, the number of tubes to emerge and the ultrastructure of these tubes are given here.MethodsPollen was germinated in vitro in different sucrose concentrations and in the presence of calcium channel blockers, and tube emergence and growth were recorded on a VCR. Measurements were taken of the number of tubes to emerge and rate of tube emergence. Pollen behaviour in vivo was also observed. The ultrastructure of germinated and ungerminated pollen was observed using TEM.ResultsAfter 10 s to 3 min in germination medium, up to three pollen tubes emerged and grew at rates of up to 55 micro m s(-1); the rate then slowed to around 2 micro m s(-1), 30 s after the initial growth spurt. Tubes were observed to grow in pulses, and the pulsed growth continued in the presence of calcium channel blockers. Optimal sugar concentration for pollen germination was 300 g L(-1), in which up to 81 % of pollen grains showed fast germination. Germination and emergence of multiple tubes were observed in sucrose concentrations of 100-800 g L(-1). The vegetative and generative nuclei moved into one of the tubes. Multiple tubes from a single grain were observed on the stigma. Under light microscopy, the cytoplasm in the tube showed a clear region at the tip. The ultrastructure of C. amoenum pollen showed a bilayered exine, with the intine being very thick at the pores, and elsewhere having large intrusions into the plasma membrane. The cytoplasm was dense with vesicles packed with inner tube cell wall material. Golgi apparatus producing secretory vesicles, and mitochondria were found throughout the tube. The tube wall was bilayered; both layers being fibrous and loosely packed.ConclusionsIt is proposed that, for Conospermum, initial pollen tube wall constituents are manufactured and stored prior to pollen germination, and that tube extension occurs as described in the literature for other species, but at an exceptionally fast rate.

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Actin polymerization is essential for pollen tube growth.

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Actin polymerization is essential for pollen tube growth.

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