The Role of Cotyledons in Flower Initiation of Pharbitis nil at Low Temperatures

概要

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Seedlings of Pharbitis nil, strains Violet, Tendan and Kidachi, initiated floral buds under continuous light when exposed to temperatures lower than 15, 15 and 21℃, respectively, throughout the experimental period, or to 13-14℃ for a minimum duration of 10, 8 and 4 days, respectively. Cotyledons were necessary for floral initiation when the seedlings at the start of cold treatment were 8 days old (10 days old for Kidachi) or younger, although neither cotyledons nor foliage leaves were necessary when the plants were older. When the cotyledons in young seedlings were removed immediately after exposure to cold temperature (13-14℃) for 14 (Violet), 12 (Tendan) or 8 (Kidachi) days (cold treatment begun when the cotyledons had just unfolded), only a few plants initiated floral buds under continuous light. However, when the cotyledons were left attached for 2 more days at 23℃, the plants produced as many flower buds as those with intact cotyledons, suggesting that cotyledons exposed to cold temperature produce a floral stimulus which can be translocated to buds even after the end of the cold treatment.