Changes in pollen tube behaviour induced by carbon dioxide and their role in overcoming self-incompatibility in Brassica |
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Authors: | T Nakanishi M Sawano |
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Institution: | (1) Department of Agriculture and Horticulture, Faculty of Agriculture, Kobe University, 657 Kobe, Japan |
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Abstract: | Summary Comparative studies on self-pollination after the application of high concentrations of CO2 gas, which is known to overcome the self-incompatibility reaction in Cruciferous species, have revealed significant changes in the pollen tubes of germinating grains prior to their penetration into the papilla cells. A remarkable increase in the width of the pollen tube was induced by treating the stigmatic papillae with high CO2 concentrations. The width of the pollen tube appeared to be greatest with CO2 concentrations ranging from 3% to 5%; these concentrations were also optimal for tube penetration. Callose accumulation was extensively induced in the stigmatic papilla with 10%–20% of CO2, although a typical callosic reaction remained through the ranges appropriate for blocking self-incompatibility. Observations using the scanning electron microscope (SEM) after pollination revealed that compatible pollen tubes in cross-pollinations fused completely to the papular surface during tube penetration, while in self-pollination, pollen tubes remained on the papilla with some additional diffusate. In the case of CO2 treatment for self-pollination, some pollen tubes behaved very similarly to the incompatible or compatible ones already described, while others were different from both of them: they showed a complete fusion, similar to compatible ones, with additional diffusate, similar to incompatible ones. These responses of the pollen and stigma to high CO2 concentrations are discussed with respect to their effect upon the expression of self-incompatibility. |
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Keywords: | Self-incompatibility CO2 treatment Pollen tube growth Brassica Diplotaxis |
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