Abstract
We screened rice mutants impaired in coleoptile phototropism from gamma-ray-mutagenized M2 caryopses of cv. Nihonmasari. Until now, three genetically separable mutants, designated as cpt1, cpt2, and cpt3 (cpt: coleoptile phototropism), have been isolated. We characterized cpt1 and cpt2 in detail. The cpt1 mutant shows no coleoptile phototropism over a wide range of blue-light fluence rates. This mutant is also impaired in root phototropism. The cpt2 mutant shows a reduced phototropic response of coleoptiles; root phototropism is normal. Tip-shading experiments revealed that, in this mutant, the tip-specific light perception is selectively impaired. In the two mutants, gravitropism and growth of the two organs are normal. Therefore, the products of CPT1 and CPT2 are probably involved in the signal transduction pathway specific to phototropism. Map-based cloning of these genes is in progress. The most recently isolated cpt3 mutant is phenotypically similar to the cpt2 mutant, but additionally shows a leaf curling phenotype.
