1) Institute of Radiation Breeding, Omiyamachi, Ibaraki-ken, 319-22 Japan
2) Institute of Nuclear Agricultural Sciences, Zhejiang Agricultural University, Hangzhou, 310029 China
Five temperature-sensitive chlorophyll mutants have been obtained. They were discovered as albino mutants in the generation after mutagenic treatments. All of them expressed an albino phenotype at high temperatures (35 deg. C), but were normal at lower temperatures (25 deg. C). They appeared to be controlled each by a single recessive nuclear gene. We examined the phenotypic expression of these mutations under varying temperature and light conditions.
Mutant lines AL7-3, 8 and 9 were induced from the variety Koshihikari, and AL40 and 44 from Norin 8, by gamma-ray irradiation of the seeds. M3 seedlings from heterozygous M2 plants were observed. Although light conditions were not controlled precisely, seedlings cultured at 35 deg.C were exposed to much more intense light than other cultures. Temperature reactions of the mutants are shown in Table 1. All of them were albino at 35 deg.C. At 25 deg.C, however, lines AL7-3, 8, 9 and 40 were green and AL44 was yellowish green. Threshold temperature differed among lines, being 28 deg.C in AL7-3, 8 and 9, 35 deg.C in AL40, and a temperature lower than 25 deg.C in AL44.
Table 1. Phenotypes of temperature-sensitive mutant lines under varying temperatures ________________________________________________________________ Temperature (deg.C) Line ______________________________________ 25 28 35 25->35 35->25 ________________________________________________________________ AL 7-3 g wg al yg new AL 8 g wg al al AL9 g yg al wg AL 40 g g al g new AL 44 yg yg al yg new ________________________________________________________________ g: green, wg: whitish green, yg: yellowish green, al: albino, new: new leaves becoming green.Seedlings incubated at 25 deg.C were then cultured at 35 deg.C. Seedlings of line AL7-3 turned to yellowish green, AL8 to albino and AL9 to yellow-whitish green, but there were no visible change in lines AL40 and 44. In turn, when seedling incubated at 35 deg.C were transferred to 25 deg.C, all the leaves which expressed chlorosis under 35 deg.C did not recover. In lines AL7-3, 40 and 44, newly formed leaves had chlorophyll to some extent.
A further experiment showed that light had an important effect on chlorophyll formation in AL44, as the phenotype became normal when the seedling were shaded at 25 deg.C.