title: Development- and light-dependent regulation of the expression of two different chalcone synthase transcripts in mustard cotyledons.
abstract: Two different chalcone synthase (CHS) transcripts show similar expression characteristics under different light regimes in cotyledons of mustard (Sinapis alba L.). Etiolated seedlings show an increase in dark-expression 36-42 h after sowing. Under continuous red or far-red irradiation both CHS transcripts start to accumulate to levels above those of the dark control at 24-27 h after sowing. This time point can therefore be considered as the starting (or competence) point for phytochrome control of CHS. Continuous far-red irradiation stimulates transcript accumulation more than red light, indicating the involvement of a high-irradiance response (HIR). Irradiation of etiolated seedlings with 5 min long-wavelength far-red light (RG9) at 6-21 h after sowing decreases CHS-mRNA levels below those of the dark control. It is concluded that CHS dark-expression in etiolated seedlings is controlled by a pool of stabletype phytochrome which is derived from seed tissue. By contrast, an RG9-light pulse given to etiolated seedlings 30 h after sowing causes accumulation of CHS-mRNA above the dark-control level. This response and the HIR are attributed to the action of labile phytochrome for which the seedling becomes competent at the starting point 24-27 h after sowing. The different starting points for CHS-mRNA expression in darkness and in light (36 h and 24 h, respectively, after sowing) also indicate that the tested CHS genes in mustard are under the photocontrol of two distinct phytochrome pools. Northern analysis shows that both CHS-mRNAs are expressed in primary leaves, epicotyls and young flower buds. In-situ hybridization with gene-specific CHS probes reveals similar expression patterns for both transcripts in cotyledons of seedlings grown under 42 h continuous far-red light.
authors.affiliation: Institut für Biologie II, Universität Freiburg, Schänzlestrasse 1, W-7800, Freiburg i.Br., Germany.
authors.forename: B
authors.initials: B
authors.lastname: Ehmann
authors.forename: B
authors.initials: B
authors.lastname: Ocker
authors.forename: E
authors.initials: E
authors.lastname: Schäfer