Cucumis属の種間交雑に関する研究-1-自家受粉ならびに不和合組合せ間の交雑受粉における花粉の発芽および花粉管の生長

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Studies have been continued in order to elucidate the mechanisms for cross-incompatibility and to transfer genes among the species of Cucumis with x=12. In this paper the behavior of pollen tubes in pistil both in cases of selfings and incompatible crossings which failed to set fruits was studied. The materials were grown in a greenhouse from March to October and ordinarily pollinated during 7-9 a.m.. Microscopic observations were carried out with pistils fixed at various intervals after pollination. The findings obtained from the experiments of selfing and incompatible crossing were summarized in Table 1 and 2 respectively.In case of selfing of several species, the longest pollen tube entered inside the stylar tissue within 20-30 minutes (Fig. 2), and reached the upper part of the ovary 4-6 hours after pollination (Fig. 4). The pollen tubes grew along the surface of placentae and entered into ovules through the micropyles in 24 hours (Fig. 5). In most of the fertilized ovules 2 or 4 endosperm nuclei were observed 48 hours after pollination and these embryo-sacs showed remarkable increase in their volume 72 hours after pollination (Fig. 7). These views indicate that the fertilization took place within 24-48 hours after the self-pollination. The results were in agreement with those of the previous reports by other investigators and no specific difference was found in the behavior of the pollen tube in case of selfing.In each incompatible crossing, the most of the pollen grains germinated on the stigma of foreign species and the pollen tubes entered inside the stylar tissue (Fig. 8, 9, 10), whereas marked differences were found in the behavior of the pollen tubes between incompatible crossings and selfings. That is, the pollen tubes in the styles of foreign species showed considerably delay or the discontinuation in their growth. Thus, almost in all the crossings pollen tubes grew only short distance and could not reach even in the lower part of the style, and their tips rarely entered inside the ovary in 24 hours. These pollen tubes frequently showed the abnormal appearence such as club-shaped swelling or branching at their tips (Fig. 8).In every crossing, where C. figarei was used as the pistilate parent, the pollen tubes could be observed in the ovary 24 hours after pollination, although these pollen tubes did not enter into ovules except a few individuals of some of the crossings. In these crossings the ovules into which the pollen tubes entered were less than in comparison to selfing of each parental species and moreover these ovules ceased development.From above mentioned results, it may be concluded that the abnormal behavior of pollen tubes in the pistil of foreign species are closely related with cross-incompatibility barriers among the species of Cucumis.

Cucumis属の種間交雑に関する研究-1-自家受粉ならびに不和合組合せ間の交雑受粉における花粉の発芽および花粉管の生長

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