Studies on the physiological mechanism of self-incompatibility in Japanese radish. I.

Influence of air humidity on self-fertility

Abstract

When Japanese radish was self-pollinated under high air humidity, its fertilizing power was enhanced to a certain degree (See Table 1, especially the results of 1963). In this case the percentage of pollen germination on the stigma was high, and some pollen-tubes penetrated into the stigma. However, no breakdown of self-incompatibility barrier was observed (Table 2).
The osmotic pressure of the stigmatic papillae measured by a plasmolytic method was isotonic to the 0.30 molal solution of sucrose two days before flowering, 0.45M on the day of flowering, and 0.35 M on the third day. The osmotic pressure of mature pollen grains was isotonic to the approximately 0.40M solution of sucrose (Table 3).
It seems probable that the poor germination of selfed pollen on the stigma is due to water deficiency because the stigmatic surface is covered with cuticule. Consequently, no inhibitory substance seems to be present on the stigma.
These results are in general accordance with those of OELKE (1957) in radish although differ somewhat in details.