Effect of High-intensity Light Given Prior to Low-temperature Treatment on the Long-day Flowering of Pharbitis nil

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Pharbitis nil, strain Violet which had been exposed to high-intensity light (18,000 lux at 23℃) for 7 days followed by a low-temperature treatment (13-14℃) for 7 days initiated flower buds even under continuous light, but plants given these treatments in reverse order failed to bud. Three days of high-intensity light at 23℃ was most effective in promoting the flower-inducing effect of the subsequent low-temperature period. Six days of low temperature following the 3-day high-intensity light period induced near-maximum flowering response. DCMU (5×10^<-6> M) given during the high-intensity light period inhibited flowering, but when given during or after the low-temperature period it was ineffective. DCMU at the same concentration given before, during or after an inductive 16-hr dark period at 26℃ did not inhibit flowering. Sucrose, ATP, NADPH and some other reducing agents tested did not nullify the DCMU effect nor substitute for the effect of high-intensity light. But, the high-intensity light effect could be substituted, at least partly, by 5-chlorosalicylic acid, 3,4-dichlorobenzoic acid and some other benzoic acid derivatives, which are highly effective in inducing long-day flowering in the short-day plant, Lemna paucicostata.