The appearance of competence for phytochrome-mediated anthocyanin synthesis in the cotyledons of Sinapis alba L.

Abstract

It is demonstrated that phytochrome-mediated anthocyanin synthesis in the epidermal cells of mustard seedling cotyledons takes place only 27 h after sowing onwards (at 25°C). This "starting point" cannot be shifted by light treatments or by nutrients. The late appearance of competence for P fr (P r and P fr, red- and far-red absorbing forms of phytochrome, respectively) with regard to anthocyanin synthesis is not related to the phytochrome system per se (P r⇆P fr) as this is fully functional immediately after sowing of the seed; nor is it related to the primary reaction of phytochrome: P fr+X→P fr X→P fr X' (X, X', two forms of a receptor for P fr) or to the initial action of P fr X':P fr X'+K'→Y' (K', coupling element, leading to the product Y', which is no longer photoreversible). Rather, the "starting point" is determined by internal factors only and is thus not accessible to any specific control by external factors. On the other hand, however, the beginning of the initial action of P fr X' ("coupling point") can be shifted by light via phytochrome under high irradiance conditions. Moreover, it is shown that there is no phytochrome-independent effect of blue light on photomorphogenesis in the young mustard seedling and that there is no "rapid dark reversion of P fr" which can be detected by physiological means, at least during.

The Photoregulation of Anthocyanin Synthesis

“…The level of anthocyanin formed under the sequences (b) and (c) is never as low as that of the dark controls; it is usually higher, showing that the photoreversibility of the effect of the light pretreatment is not complete. The only case in which a short terminal FR treatment can fully reverse the effect of a prolonged light pretreatment is when the latter is applied during the period when the biological system has not yet attained the competence for anthocyanin production in response to light (MOHR 1978, STEINITZ and BERGFELD 1977, STEINITZ et al 1976. The cause for this light-induced increase of the responsiveness to Pfr and for the change in the time course of responsiveness (SCHMIDT and MOHR 1981) is not yet understood.…”

Development- and light-dependent regulation of the expression of two different chalcone synthase transcripts in mustard cotyledons

“…Experiments to determine anthocyanin levels support these results: lower amounts of anthocyanin were obtained after an RG9 pulse than in the dark control (Oelmfiller and Mohr 1984). Anthocyanin is inducible even when light-pulse treatments are given earlier than 6 h after sowing (Steinitz et al 1976;Oelmiiller and Mohr 1984). These effects cannot be due to labile Pfr as this has too short a half-life (45-55 min) in mustard (Marm6 et al 1971).…”

“…The control o f the e n d o g e n o u s development p r o g r a m by p h y t o c h r o m e is evident from, for example, the specific starting points for the p h y t o c h r o m ed e p e n d e n t a p p e a r a n c e o f different transcripts ( W e n n g et al 1990) and enzymes (Schopfer 1984) in m u s t a r d seedlings, The starting point for C H S -t r a n s c r i p t a c c u m u l a t i o n is at a b o u t 24 h after sowing, which is similar to the time point previously determined for increases in C H S enzyme activity (Br6denfeldt and M o h r 1988). On an endp r o d u c t level, the starting p o i n t for a n t h o c y a n i n accum u l a t i o n is 3 h (Br6denfeldt and M o h r 1988; Oelmfiller and M o h r 1984; Steinitz et al 1976), and for quercetin f o r m a t i o n 6 h later (Br6denfeldt and M o h r 1988). In the case of anthocyanins, irradiation with cFR indicates the involvement of an HIR (Lange et al 1971 ;Steinitz et al 1976) as do the transcript measurements presented here.…”

“…On an endp r o d u c t level, the starting p o i n t for a n t h o c y a n i n accum u l a t i o n is 3 h (Br6denfeldt and M o h r 1988; Oelmfiller and M o h r 1984; Steinitz et al 1976), and for quercetin f o r m a t i o n 6 h later (Br6denfeldt and M o h r 1988). In the case of anthocyanins, irradiation with cFR indicates the involvement of an HIR (Lange et al 1971 ;Steinitz et al 1976) as do the transcript measurements presented here. Accumulation of CHS mRNA also occurs in dark-grown seedlings between 36-42 h after sowing.…”

Cloning and characterization of a chalcone synthase gene from mustard and its light-dependent expression

“…This observation (data not shown) makes it unlikely that UV/blue light photoreceptors are involved in CHS expression in mustard cotyledons. These effects were also described for anthocyanin accumulation [35,58].…”