Action spectra for phytochrome A- and B-specific photoinduction of seed germination in Arabidopsis thaliana.

Abstract

We have examined the seed germination in Arabidopsis thaliana of wild type (wt), and phytochrome A (PhyA)-and B (PhyB)-mutants in terms of incubation time and environmental light effects. Seed germination of the wt and PhyA-null mutant (phyA) was photoreversibly regulated by red and far-red lights of 10-1,000 ,umol m-2 when incubated in darkness for 1-14 hr, but no germination occurred in PhyB-null mutant (phyB). When wt seeds and thephyB mutant seeds were incubated in darkness for 48 hr, they synthesized PhyA during dark incubation and germinated upon exposure to red light of 1-100 nmol m-2 and far-red light of 0.5-10 ,umol m-2, whereas the phyA mutant showed no such response. The results indicate that the seed germination is regulated by PhyA and PhyB but not by other phytochromes, and the effects of PhyA and PhyB are separable in this assay. We determined action spectra separately for PhyA-and PhyB-specific induction of seed germination at Okazaki large spectrograph. Action spectra for the PhyA response show that monochromatic 300-780 nm lights of very low fluence induced the germination, and this induction was not photoreversible in the range examined. Action spectra for the PhyB response show that germination was photoreversibly regulated by alternate irradiations with light of 0.01-1 mmol m-2 at wavelengths of 540-690 nm and 695-780 nm. The present work clearly demonstrated that PhyA photoirreversibly triggers the germination upon irradiations with ultraviolet, visible and farred light of very low fluence, while PhyB controls the photoreversible effects of low fluence.

Light-Induced Nuclear Translocation of Endogenous Pea Phytochrome A Visualized by Immunocytochemical Procedures

“…In maize, light-induced gravitropic curving in roots is a very-low-fluence response, occurring in response to R, FR, or blue light (Feldman and Briggs, 1987). This response, which is very similar to other very-low-fluence responses that are known to be mediated by PhyA (Shinomura et al, 1996), strongly implies that PhyA has a role in roots. Many aspects of root development are regulated by light, including root extension, geosensitivity, and lateral root production (Furuya and Torrey, 1964); moreover, in species that show light sensitivity in the root, the region of light perception lies within the root cap (Feldman, 1984).…”

“…In this study, we have analyzed the tissue-specific distribution and subcellular localization of PHYA in etiolated wildtype pea seedlings by using immunohistochemical analysis and monoclonal anti-phytochrome antibodies (Nagatani et al, 1984(Nagatani et al, , 1987Abe et al, 1985;Lumsden et al, 1985;Shinomura et al, 1996) and the PHYA-deficient fun1-1 (FR unresponsive) mutant (Weller et al, 1997) as a negative control. Our results definitively demonstrate that native PHYA is redistributed to the nucleus in response to irradiation with continuous R or FR light.…”

“…In contrast, immunohistochemical and immunocytochemical techniques allow direct examination of the native distribution of endogenous proteins. To date, however, these techniques have not been used for specific phytochromes, largely because of the requirement for both phytochrome type-specific monoclonal antibodies and the corresponding phytochrome apoprotein-deficient mutants to serve as negative controls.In this study, we have analyzed the tissue-specific distribution and subcellular localization of PHYA in etiolated wildtype pea seedlings by using immunohistochemical analysis and monoclonal anti-phytochrome antibodies (Nagatani et al, 1984(Nagatani et al, , 1987 Abe et al, 1985;Lumsden et al, 1985;Shinomura et al, 1996) and the PHYA-deficient fun1-1 (FR unresponsive) mutant (Weller et al, 1997) as a negative control. Our results definitively demonstrate that native PHYA is redistributed to the nucleus in response to irradiation with continuous R or FR light.…”

“…Phytochromes are encoded by a small gene family (phytochrome genes PHYA to PHYE in Arabidopsis; Sharrock and Quail, 1989;Clack et al, 1994). Studies with mutants deficient in specific phytochromes have shown that phytochrome A (PhyA) and phytochrome B (PhyB) have distinct action spectra for the photoinduction of seed germination (Shinomura et al, 1996) and distinct fluence and wavelength requirements for expression of the chlorophyll a / b binding protein gene ( CAB ) (Hamazato et al, 1997). The fundamental molecular basis for these differences is of great interest but has not been elucidated.…”

Effects of sucrose and irradiance on germination and early gametophyte growth of the endangered tree fern Dicksonia sellowiana Hook (Dicksoniaceae)

“…Filippini et al (1999) Bewley & Black (1994). Shinomura et al (1996) explain that seed germination of light-sensitive species is a low fluency response (LFR) controlled by the detection of changes in the red/far-red ratio (R/FR) through phytochrome B (PHY B). Similar partial photoinhibition could be proposed for spores of D. sellowiana under 50% and 36% of irradiance.…”