The Effect Of Salicylic Acid On Physiology And Biochemistry Of Citrus Under Drought Stress

Salicylic acid (SA) belongs to a group of phenolics widely distributed in plants and is now considered a hormone-like substance, which plays an important role in the regulation of plant growth and development. In the recent years, It has received particular attention to be a signal molecule in acquired resistance to pathogens in several species, its is can be used toinduced both the synthesis of certain pathogenesis related proteins and systemic acquired resistance. Several studies also supported a major role of SA in modulating the plants response to several abiotic stresses. There has no systemic study on drought resistance of citrus treated with SA in and abroad.Potted experiment materials in greenhouse were Cara cara navel and Guoqing No.4 satsuma mandarin grafted as trifoliate stocks and trifoliate. They were treated with three levels concentration (0.1, 0.5 and 2.5 mmol/L) SA hydroponic solution by spraying onto leaves and irrigating to roots, and then were treated drought stress. This research studied the effects of physiology and biochemistry of Citrus streatment with exogenous SA under drought stress, and provide a reference to SA application in resistance of Citrus to drought.The main results in the present study are as follows:1. Under drought stress, cell membrane permeability and the content of MDA, Pro and H₂O₂ in citrus leaf and root increased. However, the relative water and chlorophyll content in leaf decreast with drough stress. At the same time, the changes of SOD, POD and CAT activity were significant and some drought protein expression was induced under drought stress.2. SA treatment had no significant influence on cell membrane permeability in citrus root, whereas it could decrease cell membrane permeability in citrus leaf. Furthermore, the degree of decrease in leaf was relative to SA concentration, test material and treatment time. For example, the cell membrane permeability in Cara cara navel orange leaf which treated with 0.1 mmol/L SA decreased by 23.63% with drought stress on 9-day. With drought stress on 7-day, the cell membrane permeability in leaf of Guoqing No.4 satsuma mandarin with 0.5 mmol/L SA treated and trifoliate with 2.5 mmol/L SA treated decreased by 15.81% and 20.06%, respectively. At the same time, SA treatment promoted accumulating in Pro which has osmotic and adjustive ability. Pro in the all Citrus root was the highest when the concentration of SA was 0.5 mmol/L. In addition, the content of Pro in Cara cara navel orange and Guoqing No.4 satsuma mandarin leaf with 0.5 mmol/L SA treated was also higher than other treatment with drough stress on 9-day. 3. During the drough stress, SA treatment decreased the content of MDA in the Citrus leaf and root. But there was no significant difference between various SA concentrations in Cara cara navel orange leaf or root, respectively. The same status was found in Guoqing No.4 satsuma mandarin. However, various SA concentrations had a significant difference in trifoliate leaf or root, respectively. On the other hand, SA treatment decreased the content of H₂O₂ in Citrus leaf by SA application, and the opposition was present in Citrus root. In addition, SA treatment could solwer the rate of this decline of relative water content of leaves and chlorophyll content.4. SA treatment increased the activity of SOD and POD in Citrus leaf and root. On the other hand, though the activity of CAT was increased in Citrus leaf by SA application, but decreased in Citrus root. By SDS-PAGE electrophoresis analysis, the results showed that some new protein band was found and the intrinsic protein band was enhanced, which could improve Citrus the resistance against drought stress.