| Plant leaves are important plant organs for organic compounds,they convert light energy into chemical energy in organic compounds for plant growth and development.Leaf senescence is accompanied by the degradation of chlorophyll,the accumulation of active oxygen,the change of plant hormone level,the increase of expression of senescence related genes,and the degradation of protein,lipid,nucleic acid and other macromolecules.Adversity often accelerates the senescence of plant leaves,leading to crop yield reduction.Delaying leaf senescence can effectively improve crop yield,and also help to prolong the shelf life of leafy vegetables.Melatonin is first found in animals,which is involved in regulating circadian rhythm,immunity,reproduction and other important physiological activities.Melatonin also widely exists in plants,it is involved in seed germination,root formation,flowering,fruit maturity and other growth and development processes.At the same time,as a strong antioxidant,melatonin is widely involved in the response of plants to various biological and non biological stresses.Some studies have found that it can alleviate plant aging,but the mechanism of melatonin to alleviate plant aging is not clear.100 ?mol/L melatonin was used to treat Arabidopsis wild-type Col,deletion mutants(snat-2,sid2 and wrky75)and WRKY75 overexpression plants(WOE-3/-6)in our study.The senescence of plants was observed by phenotype,chlorophyll content,active oxygen accumulation leveland cell death;study on the relationship between melatonin and salicylic acid during the senescence of Arabidopsis leaves by measuring the contents of melatonin and salicylic acid and the gene expression of SNAT,SID2 and WRKY75,and also discuss the role of transcription factor WRKY75 in this process.The main results of this study are as follows:1.Exogenous melatonin can alleviate the senescence of Arabidopsis leaves.In the process of senescence,the accumulation of melatonin in plant leaves is decreasing;exogenous melatonin promotes the accumulation of endogenous melatonin by up regulating the expression of SNAT gene;at the same time,by alleviating the decrease of chlorophyll content,accumulation of active oxygen,cell death and the expression of SAG13,and the senescence of Arabidopsis leaves was delayed.In addition,melatonin plays an important role in plant growth and development before plant aging,the absence of SNAT will delay the development of plant,and then delay the triggering of aging related factors.2.Exogenous melatonin can delay the senescence of Arabidopsis leaves through salicylic acid pathway.Melatonin can reduce the accumulation of salicylic acid by down regulating the expression of SID2 gene,and then alleviate the senescence of plant leaves.Lack of salicylic acid can increase the expression of SNAT gene and increase the accumulation of melatonin,indicating that salicylic acid negatively regulates the accumulation of melatonin.In the absence of salicylic acid,exogenous melatonin can still alleviate the senescence of the leaves of sid 2 plants,but compared with the wild type,the extent of melatonin alleviating senescence in sid2 mutants is significantly smaller,which shows that salicylic acid is only one of the ways of melatonin alleviating the senescence of the leaves of plants,and melatonin can also delay the senescence of the leaves of plants through other ways.3.Exogenous melatonin alleviates Arabidopsis leaves senescence through down regulated WRKY75 expression.Exogenous melatonin can inhibit the expression of senescence related genes by down regulating the gene expression of transcription factor WRKY75,and alleviate the senescence of plant leaves.The effect of wrky75 deficiency on the expression of SNAT and the accumulation of melatonin was not consistent,indicating that the effect of WRKY75 on the pathway of melatonin synthesis was complex.4.Melatonin and the WRKY75-SA-ROS amplification loop have opposite effect on senescence,thus regulating plant senescence related events,and delaying Arabidopsis leaf senescence. |
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