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

Abstract

Kroh (1966) reported that self-incompatible pollen grains after being placed for a short time on the stigmatic surface of foreign plants were able to penetrate the self-stigma, in Arabis arenosa and Brassica nigra. She concluded that the cutinase of the pollen was activated irreversibly during the short contact of pollen grains with a foreign stigma. On the other hand, the results of Kanno et al. (1967) with Diplotaxis ercoides and Brassica nigra disagreed to those of Kroh.In these experiments two cultivars of self-incompatible and cross-compatible Japanese radish, Shogoin and Minowase, were used as materials. Pollination and the transfer of pollen from one stigma to another were carried out at 22°C using a fine needle. Since some of the pollen grains germinated within 35-40 minutes after cross- pollination, the transfer of pollen after self-or cross-pollination was started 20 minutes after the pollen grains were brought on the stigma. Pollen and stigma were combined as follows (after Kroh): I (crossing→crossing), II (selfing→crossing), III (selfing→selfing) and IV (crossing→selfing). The behavior of pollen on stigmas was examined by the following procedure: The pistils were collected 24 hours after pollination, fixed and stained with 0.5 percent lactic-blue for fourhours, differentiated with lactic acid for about 24 hours and finally mounted with glycerine.The results obtained were presented in Tables 1-3. In the experiment of 1967, the results of combination IV disagreed to those of Kroh (Table 1). Only two experiments, combinations III and IV, were performed in 1968. However these experiments were unsuccessful because of poor technique (Table 2). Through training for pollination technique, the identical experiments were carried out in 1969 and 1971. Table 3 shows that the percentage of pollen germination in combination IV was much superior to that in combination III. Some compatible pollen grains whose tubes penetrated the stigma were found in combination IV, but few in combination III. However the tubes of compatible pollen were generally short. A few emptied pollen grains which had transferred their contents into their tubes were recognized in combination IV.These results are in agreement to those of Kroh. It seems probable that the inactive enzyme of the pollen is to some extent activated irreversibly, during the short contact of pollen grains with a foreign stigma.