Temporal And Spatial Localization Of Stigmatic Factors Involved In Pollination In Arabidopsis Thanliana

Angiosperms produce seeds by following sexual reproduction. Pollination is of importance for successful sexual reproduction, thus it is valuable for grain-production and theoretical research elucidating the pollen-stigma interaction in the process of pollination. After landing on stigma, arabidopsis pollen adheres, hydrates, germinates and pollen tube penetrates and elongates. Lots of researches have been made: pollen exine was reported to be involved in pollen adhension and pollen coat proteins were found to function in pollen hydration. Still little is known about the mechanisms regulating pollen-stigma interaction. In this study, we observed pollen-stigma interaction by transmission electron microscope, and tested the temporal and spatial localization of stigmatic factors regulating pollen hydration and germination in Arabidopsis. We found that:(1) Pollens and pollen tubes were actively metabolic cells with lots of cellular organelles and membrane vesicles were observed at the site pollen germinating; the centre of papillar cell was occupied by large central vacuole which was surrounded by cytoplasm and nucleus; no transport vesicle but expansion of papillar cell wall was observed at the site contacting pollen and pollen tube.(2) Stigmatic surface of pistils at developmental stage 9 was able to support pollen hydration, while distal end surface of pistils at stage 8 could not support pollen hydration; Time course of pollen hydration was similar (about 240 seconds) on different stigmatic surfaces at developmental stage 9-13.(3) Pollen germination was observed on stigmatic surface of pistils at stage 9 though pollen tubes were shorter that on stigmatic surfaces at stage 10-13; no pollen germination was observed on distal end surface of pistils at developmental stage 8 even after pollen hydration barrier overcome in 100% relative humidity.(4) By Nile red staining, Strong green fluorescence and small finger-like papillar cells were observed on the stigmatic surface of pistils at stage 9 but not on the distal end surfaces of pistils at stage 8. (5) Pollen germination was observed on the immature floral organs at stages 9 to 12 after pollen hydration barrier overcome in 100% relative humidity.We suggest that stigmatic factors regulating pollen hydration and germination are synthesized accompanying with differentiation of papillar cell at developmental stage 9. Time course of pollen hydration is similar on different stigmatic surfaces at developmental stages 9-13; initiation of pollen hydration requires stigmatic factors but rates of pollen hydration is controled by pollen. Different factors are required for pollen hydration and germination, respectively; the factors regulating pollen hydration were confined on surface of stigmas after stage 9, while the factors regulating pollen germination localized on young floral organ surfaces at stage 9-12 and stigmas after developmental stage 9. We studied the temporal and spatial localization of stigmatic factors involved in pollen hydration and germination, which provides accurate information for identification of stigmatic factors involved in pollen hydration and germination by transcriptomics methods.