title: The circadian oscillator is regulated by a very low fluence response of phytochrome in wheat.
abstract: Expression of genes encoding the light-harvesting chlorophyll a/b binding proteins of photosystem II (Cab) in etiolated wheat seedlings is controlled by phytochrome and a circadian clock. Even photoconversion of <1% of phytochrome to its active form, which can be achieved by moonlight, induces the expression of the Cab genes, particularly that of the Cab-1 gene, in circadian fashion. Thus, this reaction shows the characteristics of a low and a very low fluence response. A single far-red light pulse given to an etiolated seedling is sufficient for a persistence of the circadian oscillation of the Cab-1 mRNA level for at least 100 h. Subsequent red (R) or long-wavelength far-red (RG9) light irradiations alter the free running rhythm. These observations indicate a change in sensitivity to phytochrome and/or a control by stable phytochrome. The latter hypothesis is supported by the observation that the level of Cab-1 mRNA is increased or decreased by a second R or RG9 light pulse, respectively.
authors.affiliation: Friedrich-Miescher Institut, Basel, Switzerland.
authors.forename: F
authors.initials: F
authors.lastname: Nagy
authors.forename: E
authors.initials: E
authors.lastname: Fejes
authors.forename: B
authors.initials: B
authors.lastname: Wehmeyer
authors.forename: G
authors.initials: G
authors.lastname: Dallman
authors.forename: E
authors.initials: E
authors.lastname: Schafer