| Budget Amount *help |
¥4,000,000 (Direct Cost: ¥4,000,000)
Fiscal Year 1998: ¥400,000 (Direct Cost: ¥400,000)
Fiscal Year 1997: ¥3,600,000 (Direct Cost: ¥3,600,000)
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| Research Abstract |
Two physiologically distinct classes of phytochrome seem to regulate the many diverse red light-stimulated responses in the fern haplophase. The classes include dichroic phytochrome and non-dichroic phytochrome. The responses regulated by the former show action dichroism under polarized light while those regulated by the latter do not. The involvement of dichroic phytochrome is particularly evident in phototropism and the chloroplast relocation response. In the present work, red-light aphototropic (rap) mutants of the fern Adiantum capillus-veneris were isolated and characterized physiologically and molecular biologically. Five rap mutants, rap2, rap7, rap32, rap33, rap39 were obtained from EMS-mutagenized spores. The rap mutants lacked red light polarotropism but still retained normal blue light phototropism and polarotropism. Treatment with biliverdin, a precursor of phytochrome chrormophore had no effect on the red-light aphototropic nature of rap mutants. Analyses on the other phot
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oresponses revealed that phytochrome-mediated chloroplast relocation movement was missing in the mutants whereas the response induced by blue light was normal. Phytochrome regulation of spore germination, tip growth and cell division were also normal in the rap strains. These results indicate that phototropism and chloroplast relocation movement share the same dichroic phytochrome and the following signal transduction steps. Moreover, it shows that this pathway is distinct from that controlling spore germination, tip growth and cell division. The rap mutants may have defect(s) in the photoreceptor molecule itself, in the binding mechanism to a stable structure, or in elements involved early in the dichroic phytochrome-mediated signal transduction pathway. Next, another rap mutants (hrap11 and hrapl3) were isolated from the spores mutagenized by heavy ion beam. Genomic Southern blot analysis using phytochrome cDNAs revealed that one of the phytochrome genes, PHY3 was missing in hrapl3 mutant. Now we are testing whether the phenotypes are rescued by transforming hrap13 mutant with PHY3. Less
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