Biochemistry of Short-Day and Long-Day Flowering in Pharbitis nil(Physiology and Biochemistry of Flowering, For Further Development of Horticulture in East Asia)

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Pharbitis nil has been widely used as a typical short-day plant in studies of flowering. It can be induced to flower by a single dark treatment even in seedling with just unfolded cotyledons. This plant is also capable of inducing to flower under continuous light by giving various treatments such as poor nutrition (PN), high-intensity light (HL), low-temperature (LT) and physical or chemical inhibition of root elongation etc. Furthermore, the responses to these treatments were different among strains. Therefore, it is a suitable experimental material to study the mechanism of floral induction. We are investigating to elucidate the mechanism of floral induction under various conditions by using Pharbitis nil, strain Violet, Kidachi and Tendan. In this symposium, we will report two subjects on flowering in Pharbitis nil, (1) the mechanism of floral induction of long-day (LD) flowering by PN, HL and LT, (2) our recent works on short-day flowering. Pharbitis nil, strain Violet, is induced to flower under continuous light by PN, HL and LT, but strains Kidachi and Tendan were not by PN and HL, though they initiated floral buds under LT. HL has interesting effects on flowering, that is, (1) induction, (2) promotion of LT flowering, (3) inhibition of short-day flowering. The cotyledons are necessary for flowering under these conditions. Therefore, we widely analyzed the extracts from the cotyledons by using HPLC equipped with various detectors. As the results, we found several substances which closely correlated with flowering. Floral induction under PN and HL is closely correlated with the accumulation of some phenylpropanoids such as chlorogenic acid (CGA), p-coumaroylquinic acid (CQA) and pinoresinol-β-D-glucoside (PRG), sugars such as glucose, fructose and sucrose, and polyamine such as putrescine (PUT). Under LT, feruloylquinic acid (FQA) and ascorbic acid instead of CGA and PRG increased preceding floral initiation. Promotive and inhibitory effects of HL on flowering can be explained by the action of ascorbic acid. High level of sugars is necessary condition and the accumulation of CGA, PRG, FQA and/or PUT seems to be sufficient condition, that is, floral initiation under long-day condition always occurred when necessary-sufficient condition was fulfilled. In order to elucidate the physiological roles of these phenyl-propanoids, we remarked PRG, which is known as an inhibitor of phospho-diesterase (PDE). Inhibitors of PDE such as papaverine, theophyline and caffeine promoted flowering under PN. Moreover, FQ and some benzoic acid derivatives which promoted LD flowering inhibited the activity of PDE, suggesting the involvement of c-AMP in LD flowering. It will be described about the endogenous level of c-AMP in relation to PN flowering. In pattern analysis by using HPLC, it was difficult to find out florigen-like substance in extracts from photoperiodically induced leaves. Recently, we found that the inhibitors of biosynthesis and degradation of catecholamines (CA) inhibited floral initiation when they were applied before and during the dark period. Thus, we introduced a coulometric array system (ESA-Coulochem), which can measure CA at f mol level, for the quantitative measurement of CA. Unexpectedly we failed to detect CA, but we found many substances which seem to be florigen. It will be referred to their results.
1998-11-15

Biochemistry of Short-Day and Long-Day Flowering in Pharbitis nil(Physiology and Biochemistry of Flowering, For Further Development of Horticulture in East Asia)

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