Forty-two genotypes from the rice germplasm (Oryza sativa L.) were identified under chilling temperature in the light at bud, seedling and booting stages and divided into three basic types; cultivars tolerant to chilling in the light such asjaponica, cultivars sensitive to chilling in the light such as indica and cultivars that have intermediate tolerance to chilling in the light such as hybrid rice cultivar. Photosynthetic characteristics of two cultivars tolerant (c.v. Taipei309 and Wuyujing3), two cultivars sensitive (c.v.CA212 and Pusa) and two intermediated tolerant (c.v. Liangyoupeijiu and Shanyou63) to the chilling treatment in the light were compared. The results showed that, compared to the rice varieties chilling tolerant rice, the sensitive ones indica exhibited a significant inhibition of maximum photosynthetic rate (Pm) and a decrease in the photochemical efficiency of photo-system 2 (PS2)( Fv/Fm), which led to the accumulation of AOS and decrease of Chl content. Interestingly, the ratios of ASA/DHA and GSH/GSSG showed similar changes as those with the performance of chilling tolerance, which indicated that ASA/DHA cycle might be an important protecting strategy in chilling tolerance, especially for the middle tolerant ones. We describe a simple and effective screening method and physiological basis for breeding crops for enhanced tolerance to chilling temperature in the light.
Key words: Rice, chilling tolerance, photosynthetic rate, photo-system, chilling stress, photooxidation, gluthione, ascorbate.
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