|Budget Amount *help
¥2,100,000 (Direct Cost : ¥2,100,000)
Fiscal Year 1993 : ¥600,000 (Direct Cost : ¥600,000)
Fiscal Year 1992 : ¥1,500,000 (Direct Cost : ¥1,500,000)
In this research we have examined how and why Cymbidium flower buds become blasted by high temperature using a high temperature tolerant mutant and another non-tolerant cultivar. The tolerant mutant isolated from a mericlone revealed the same somatic chromosome number of 2n=40 as its original cultivar (Ruby Eyes 'Golden Star'). The mutant produced a smaller amount of pollen, which suggests some abnormal events in microsporogenesis. Among mutant plants propagated by meristem culture, non-tolerant ones were also found. Therefore, we have tried to distinguish them from tolerant mutants. However, this was only done for very limited number of mutants. Because, most mutant plants did not initiate inflorescences probably due to after-effect of division conducted in 1992
For the above reason, further experiments were carried out with the non-tolerant cultivar(Sazanami 'Haru-no-umi'). When plants grown at low temperatures(20ﾟC day/14ﾟC night)were transferred to high temperatures(30ﾟC/24ﾟC), absc
isic acid(ABA)content of flower buds increased up to 5 fold of the initial content. Onthe contray, that of control ones remained around the initial level. Under low temperature conditions, exogenous ABA lowered growth rate of flower buds. Some of ABA-treated flower buds became blasted resulting in reduced flowering. Inhibitory effect of ABA was abolished by gibberellic acid(GA_3).
We also examined effect of an GA biosynthesis inhibitor uniconazole on flower bud development. Uniconazole-treated flower buds evolved much more ethylene than control ones and finally became blasted. The effect of uniconazole was completely reversed not by GA_3 treatment but by combined application of GA_3 with silver thiosulfate. These results revealed participation of GA in flower bud development, and also supported the hypothesis proposed based on previous studies that high temperature causes GA deficiency and/or GA insensitivity of flower buds, which in turn leads the flower buds to blasting though stimulating ethylene evolution. Less