Abstract:

To elucidate the physiological mechanism of differential cold tolerance in rice, japonica rice cultivars 9516, H45, WuyuJing, PEPC transgenic rice, Kitaake, Su huxiangjing; indica rice cultivars Yangdao 6, Xiangxian, IR64, Peiai64S and hybrid rice cultivars Yueyou 938, Shanyou63, X07S/Zihui 100, Liangyou Peijiu, 14 rice cultivars were appraised for cold tolerance at early seedling stage, seedling stage( 3 blade) and booting stage, respectively(Table 1). At the same time, the identification of cold tolerance in rice in natural chilling condition was conducted in Nanjing(Fig.1). Results showed that the method for identifying cold tolerant rice cultivars at bud stage, seedling stage and booting stage is feasible and bud livability, seedling mortality and seed-setting rate of rice are reliable indexes for cold tolerance identification which are correlated with some physiological parameters in different rice cultivars under chilling treatment. Furthermore, photosynthetic rate(Fig.3), PSⅡ photochemical efficiency(F_v/F_m)(Fig.4), the composition of fatty acid(Table 2), the changes of active oxygen index(MDA, H₂O₂ and O₂^．- ) and anti-photooxidative substance(ascorbate and glutathione) (Table 3) of cultivars with a different tolerance to chilling were studies before and after chilling treatment. The results showed that photosynthetic rate and PSⅡ photochemical efficiency(F_v/F_m) in leaves of tolerant cultivar Wuyujing were kept stable, while those in the sensitive one, Xiangxian, decreased more and in the middle one, Shanyou 63, kept in a middle range. And the index of unsaturated fatty acid was higher in tolerant cultivars, while the recycle of ascorbate and glutathione in leaves, particularly the turnover of glutathione in leaves in the middle tolerant cultivar Shanyou63 activated highly as compared with the sensitive one, Xiangxian. It is indicated that the cold tolerance rice cultivars keep higher index of unsaturated fatty acid and capacity for turnover of glutathione, which exhibited stable photosynthetic rate and primary PSⅡ photochemical efficiency(F_v/F_m) in leaves after chilling treatment.

Key words: Rice, Chilling tolerance, Physiological basis