Photophysiology and Phytochrome Content of Long-Hypocotyl Mutant and Wild-Type Cucumber Seedlings

Abstract

Photomorphogenetic responses have been studied in a cucumber (Cucumis sativus L.) mutant (lh), which has long hypocotyls in white light (WL). While Photomorphogenesis in higher plants is a complex process regulated by a number of different photoreceptors, including phytochrome, cryptochrome, and UV-B photoreceptor (13,14). In addition, there is evidence for multiple types of a particular photoreceptor (e.g. the light-stable and light-labile types of phytochrome [20, 21], sometimes referred to as green-plant and etiolated-plant phytochrome, respectively). There is interaction between these photoreceptor systems in time and space during differentiation (13,14). The interpretation of physiological experiments is therefore often difficult, if not impossible, particularly in experiments utilizing light which is absorbed by more than one photoreceptor, as is the case for phytochrome and cryptochrome in the BL1 region of the spectrum (8, 13). To understand the roles played by the different photoreceptor systems we have taken a genetic approach in an attempt to resolve the inevitable confusion that has arisen (1,(10)(11)(12) MATERIALS AND METHODS Plant Material. The long-hypocotyl (1h) mutant and isogenic wild type of Cucumis sativus L. used here have been described elsewhere (1).Light Sources. White light was obtained from Philips TL40/33 fluorescent tubes. The broadband light sources for BL, RL, and FR used in long-term growth experiments were qualitatively the same as those described previously (11), and the fluence rates utilized are given in the figure legends. In short-term growth experiments, narrow-band BL (459 nm) and RL (658 nm

Photophysiology of the Elongated Internode (ein) Mutant of Brassica rapa

“…Light-grown ein seedlings do not display a growth promotion by end-of-day FR, whereas this response is observed in normal seedlings. End-of-day FR growth promotion, which has become a standard 'assay' for the action of light-stable phytochrome (10), is also not observed in the Arabidopsis hy3 and cucumber Ih mutants (1,14). Additionally, the first intemode of ein seedlings displays only a small growth promotion in response to seedling growth under low R/FR.…”

Overexpression of Phytochrome B Induces a Short Hypocotyl Phenotype in Transgenic Arabidopsis.

“…The long hypocotyl aurea mutant of tomato is deficient in light-labile phytochrome A (Parks et al, 1987) but retains normal levels of light-stable phytochrome (Adamse et al, 1988~). Conversely, based on photobiological studies, it has been proposed that the Ih long hypocotyl mutant of cucumber (Adamse et al, 1987(Adamse et al, , 1988b) and the hy3 long hypocotyl mutant of Arabidopsis are deficient in lightstable phytochrome but have normal levels of light-labile phytochrome (Adamse et al, 1988a). The hy3 mutant has now been shown to be deficient in phytochrome B, the predominant light-stable phytochrome thus far examined in Arabidopsis (Somers et al, 1991).…”

The cucumber long hypocotyl mutant lacks a light-stable PHYB-like phytochrome.

“…Two photomorphogenic mutants that are physiologically very different from each other are the aurea (au) of tomato (Koornneef et al, 1985;Adamse et al, 1988b) and the long hypocotyl (Ih) of cucumber (Adamse et al, , 1988a; their characterization has led to the suggestion of separate functions for the different molecular species of phytochrome (for review, see Kendrick and Nagatani, 1991). It is of interest to ascertain whether such closely related proteins have separate biological roles.…”