Effects Of Melatonin On The Structure And Function Of Photosystem ? Under High Light Stress

Light is the energy and basic power of photosynthesis and the lack of light can restrict photosynthesis seriously.However,the excess light would damage photosystem and inhibit photosysthesis,which would affect plant growth and development,resulting in plant death and crop yield reduction.In order to avoid the light damage,plants have therefore formed diverse adaptation mechamisms in the long-term evolution process.The most important mechamism is to clear the reactiove oxygen species and repair the optical system quickly,so that the photosystem can maintain the normal function of photosysthetic.Melatonin has been a research hotspot in recent years since it has the function of scavenging reactive oxygen species as antioxidants.This experiment was based on the Arabidopsis thaliana Columbia wild type and snat-1 and snat-2,which is a genetic background of Columbia.The effects of melatonin on physiological parameters under high light and the function and strcture of photosystem were examined,and the mechanism of melatonin alleviating photosystem damage under high light was studied.The main results of this study are as follows:1.The melatonin content in the mutants(3.25 ng g^-1 FW and 3.24 ng g^-1 FW in snat-1and snat-2 respectively)was significantly lower than that in wild type(13.04 ng g^-1 FW).The melatonin content in wild type and mutants was increased significantly after exogenous melatonin applied,and increased significantly under the high light stress,and further increased with high light after appliying melatonin;2.There were no significant differences in phenotypic,biomass and pigment content between wild type and mutants under the growth light.Pigment content decreased significantly under high light and wt,snat-1 and snat-2 decreased by 29.92%,33.33%and53.14%respectively.Exogenous melatonin could alleviate the degradation of pigment.3.There were no significant differences in the level of reactive oxygen species,the lipid peroxidation,the osmotic regulator and the cell death between wild type and mutants under the growth light.High light caused accumulation of reactive oxygen species and destruction of membrane integrity.The mutants were affected more seriously than wild type under high light.Expgenous melatonin alleviated the oxidative damage by altering the activities of antioxidant enzymes and the contents of non-enzymatic antioxidants.4.There were no significant differences in photosynthetic system functions between wild type and mutants in growth light from the photosynthetic parameters and chlorophyll fluorescence parameters.The photosystem activity decreased with the high light stress,and the mutants were more seriously.Melatonin could alleviate the decline of photosystem activity.5.Western blot analysis showed that the contents of photosystem proteins in the mutants was lower than that in the wild type,and the high light led to the proteins content decreased significantly in the wild type and mutants.Melatonin treatment could alleviate the decrease of the proteins content of the photosystem caused by the high light stess.