The Mechanism Of Protection From Low Temperature Photoinhibition In Rice (Oryza Sativa L.) Following 5-Aminolevulinic Acid Feeding

Photosynthesis is the basis of growth and development of plant,it provides the substrates and energy for growth and development.Low temperature as well as high light intensity stress effects photosynthesis.Therefore,it is important to study the mechanisms that how the stress effects photosynthesis.ALA is a key precursor in the biosynthesis of porphyrins such as chlorophyll and heme,Its high concentration is used as a herbicide,and in low concentration,it can judge growth,increase production of crop,and heighten resistance to salt and cold adaptability.We studied the influences of exogenous 5-aminolevulinic Acid(ALA) on photochemical efficiency, thermal dissipation,photochemical reaction and other physiology process of photosystemâ…¡and analyzed its regulation on photosystemâ…¡under low temperature as well as high light intensity in rice.Our results suggested that the excess energy was mainly reduced by thermal dissipation.However,ALA could adjust the allocation of absorbed energy and increase energy flowing to photochemical so as to reduce excess energy in leaves.Moreover,ALA also could alleviate harm to the acceptor of PSâ…¡, maintain the higher electron-transferring activity,keep QA to do oxygenation under low temperature as well as high light intensity and reduce inactivation of PSâ…¡reaction centre so as to enhance the stability of PSâ…¡under low temperature as well as high light intensityThe another mechanism of significant increase in resistance to low temperature photoinhibition was studied.Low concentration ALA-treatment enhanced the resistance of rice,because of the significant enhancement of the ascorbate peroxidase (APX) and glutathione reductase(GR) activities as well as the less reduce in superoxide dismutase(SOD) activities which alleviate photoinhibition of photosystem 2 by reducing accumulation of the hydrogen peroxide(H₂O₂) in chloroplast instead of the enhancing of thermal energy dissipation by xanthophylls cycle.Moreover,the increased activity of the ascorbate peroxidase(APX) was probably resulted from the accumulation of heme content.