Effects Of Salicylic Acid On Physiology And Biochemistry Of Rice (Oryza Sativa) Under Low Temperature Stress

Salicylic acid (SA) belongs to a group of plant phenolics widely distributed in plants and is now considered as a hormone-like substance, which plays an important role in the regulation of plant growth and development.In this paper, the possible physiology and biochemistry metabolism of enhancement of cold tolerance by SA in rice seedlings (Oryza saliva L.var. E-you540) was studied. Measurements of leakage electrolyte following chilling stress for 0-8d at 7℃ showed that pretreatment with hydroponic solutions containing 1mmol/L SA as foliar spray under normal growth conditions 25℃ could significantly enhance cold tolerance of rice plants. The results showed that SA lowered the leakage rate of electrolyte in rice leaves and roots, indicating that SA alleviated chilling damage. SA pretreatment increased the contents of protein, chlorophyll, chla, chlb and carotenoid of rice leaves, and it also enhanced the water holding of rice leaves. SA pretreatment could alleviate the chilling stress on rice seedlings.To investigate the antioxidant defense system, the changes of antioxidant enzymes were examined in the leaves and roots of rice pretreated with SA and H2O. SA preferentially enhanced the activity of superoxide dismutase (SOD), peroxidase (POD) special to guaiacol, but it induced the decrease of catalase (CAT) activity. In order to analyze the effects of SA on antioxidant enzymes isoforms under chilling stress, foliar extracts were subjected to native PAGE. Leaves of SA-treated and SA-untreated rice seedlings had six SOD isoforms and roots had three. Expressionof SOD was preferentially enhanced by chilling stress, and the intensities of SODexpression in SA-treated rice seedlings were higher than that in SA-untreated rice. As for POD, there are seven isoforms in leaves and nine in roots of SA-treated rice seedlings. And there are six bands in leaves and seven in roots of SA-untreated rice seedlings. It suggested that both SA-treated and SA-untreated rice seedlings had only one CAT isoform in their leaves and roots. These results collectively suggested that chilling stress activates the enzymes of SOD and POD under catalase deactivation in the leaves and roots of SA-treated and SA-untreated rice, and SA enhanced expression of POD and SOD under low temperature, and there was different ROS scavenger enzymatic system expression pattern in leaves and in roots.Effects of SA on expression of AOXl enzymes and the transcription of Aoxl gene encoding AOXl enzymes were also studied. The results showed that the level of Aoxl transcript of SA-treated and SA-untreated rice leaves were enhanced by chilling stress, and the level of Aoxl mRNA of SA-treated rice leaves were higher than that of SA-untreated rice leaves. This suggested that SA could enhance the transcription of Aoxl gene and the expression of AOX enzyme, alleviated the ROS production in the mitochondria and increased tolerance to chilling.