光照条件下低温对水稻籼粳亚种幼苗抗氧化物质含量的影响

与对低温不敏感的粳稻台北309和武育粳相比,对低温敏感的籼稻IR64、CA212和Pusa经光照条件下8℃处理后最大光合速率(Pmax)和原初光化学效率(Fv/Fm)下降较多,出现了O2-·、过氧化氢、氧化型谷胱甘肽(GSSG)和氧化型抗坏血酸(DHA)的大量累积,其GSSG和DHA的含量分别与叶绿素含量的下降呈极显著负相关,表明光照条件下低温胁迫下,还原态的谷胱甘肽(GSH)和抗坏血酸的再生受阻,不能有效地清除活性氧,导致其叶绿素含量降低和光合能力受抑,而汕优63的变化位于上述两种类型之间。其中AsA/DHA和GSH/GSSG的变化与叶绿素含量的变化呈极显著正相关。

Effects of Low Temperature in the Light on Antioxidant Contents in Rice(Oryza sativa L.) Indica and Japonica Subspecies Seedlings

To study the nature and mechanisms of resistance of rice plants to chilling stress, the effects of low temperature treatment (8 degrees C) on the photosynthetic rate and some important compounds forming redox cycles were measured. The rice varieties used are two japonica rice varieties, i.e., Taipei 309 and Wuyujing; three indica rice varieties, i.e., IR64, Pusa and CA212; and one intermediate type, i.e., Shanyou 63. Three types of varieties were studied by comparing. The light intensity-photosynthesis curves, CO2-photosynthesis curves, primary photochemical efficiency (Fv/Fm), active oxygen species (AOS) (O2*- and H2O2), glutathione (both oxidized and reduced forms) and ascorbate contents in their six-week old seedlings were measured before and after chilling treatment. The results showed that relative to the rice varieties chilling tolerance such as Taipei 309 and Wuyujing, the sensitive ones indica IR64, Pusa and CA212 exhibited a stronger inhibition of maximum photosynthetic rate (Pmax) (Figs.1 and 2) and a decrease in Fv/Fm (Fig.3), which led to the accumulation of AOS (Fig.6). It was found that the glutathione disulphide (GSSG) content in glutathione pool and that of dehydroascorbate (DHA) in ascorbate pool of the leaves of these sensitive ones under chilling were induced to increase obviously (Table 3). The correlation coefficient between the increases in GSSG, DHA and the decrease of Chl content were -0.701**, -0.656** respectively (Table 4). This indicated that the regeneration of reduced glutathione (GSH) and ascorbate was inhibited, resulting in accumulations of AOS and the reduction of Chl content (Fig.4) and the inhibition of photosynthetic activity (Fig.1 and Fig.2). The changes in japonica Taibei 309 and Wuyujing were small. And the changes in indica hybrid were lying between the above-mentioned types. Particularly, the ratio of AsA/DHA and GSH/GSSG (Fig.7) showed similar changes as those in Chl content (Fig.4). The correlation coefficient among Chl content and AsA/DHA, GSH/GSSG were 0.811**, 0.728** respectively (Table 4), significant at 0.01 probability levels. The levels of AsA/DHA and GSH/GSSG ratio in rice leaves may be the physiological indexes associated with the sensitivity to chilling in rice varieties.