Study On The Protective Effect Of Exogenous Melatonin On Rhythm Of Hulless Barley Endogenous Biology Under Cold Stress

Circadian rhythm is an endogenous time-keeping mechanism that is ubiquitously existed in living organisms.The circadian rhythm in an organism controls not only the transcriptional activities of clock genes,but also the translation/accumulation/modification and degradation processes of proteins,so as to the following control of physiological and biochemical behaviors of given organisms.Melatonin is an indole hormone.Present researches on the function of melatonin in plants is on it's roles in seedlings or certain organs'growth regulation,as well as in enhancing the tolerance of plants to either biotic or abiotic stress.There are still less researches that have been conducted on the function of melatonin in the process of plant circadian rhythms moduling.Hulless barley is a cereal crop that grows on the Qinghai-Tibet Plateau at an average altitude of 4500 meters.Researches show that barley is originated from oriental cultivated barley and was introduced into the Qinghai-Tibet Plateau through the Nepal region 3500-4500years ago.In the Qinghai-Tibet Plateau,hulless barley is a widely distributed cereal crop which could resist the harsh natural environment of the Qinghai-Tibet Plateau,such as ultraviolet radiation,drought,salt stress,cold stress and so on.In recent years,with the accomplishment of the genome and transcriptome sequencing in hulless barley under seedlings under various stresses,the mechanism of stress resistance in barley also have been rapidly explored.However,the researches held in hulless barley is still not deep enough to explain the detail molecular mechanism to the very strong ability in the stress-resistant of this plant,and much more further researches are still necessary.To reveal how melatonin had functioned in the regulation of plant circadian rhythms,exogenous melatonin pretreated hulless barley seedlings were used as material in this dissertation to study phenotypes of plant growth,as well as their circadian rhythms at transcriptional,translational,physiological,and biochemical levels under different temperature conditions.The contents and results of the research works that described in this dissertation are listed as follows:1. Under cold stress,pretreatment with exogenous melatonin can promote the growth of barley seedlings and restore the expressional rhythmicity of some circadian genesThe results show that circadian clock genes in control seedlings can maintain a good rhythmic phenotype at 25?and 15?,while the circadian clock genes completely lost their expressional rhythmicities at 5?.While the seeds of barley were pretreated with 1?M exogenous melatonin solution,the core clock genes,such as Hv TOC1 and Hv CCA1,could restore the rhythmic of transcription to various extents at 5?.2. Under cold stress,pretreatment with exogenous melatonin can restore the rhythmic accumulation of hydrogen peroxide and some antioxidant enzymes in barley seedlings.At 25?or 15?,the hydrogen peroxide and some antioxidant enzyme activities in control barley seedlings had a phenotype of rhythmic accumulation.When they were transplanted under 5?,the rhythmic accumulation of hydrogen peroxide and some antioxidant enzymes in control seedlings were negatively affected due to cold stress.When the barley seed was pretreated with an exogenous melatonin solution at 1?M,hydrogen peroxide and SOD,CAT,and Hv SOD1 activites rhythmically oscillated in seedlings for at least 48h at 5°C.3. Under cold stress,pretreatment with exogenous melatonin can restore the circadian oscillation of the PRX-SO_2/3 rhythmic marker.At 25?,the transcription-independent PRX-SO_2/3 rhythmic marker in barley exhibits a good circadian rhythmic phenotype,while at 15°C and 5°C,the rhythmic oscillation of which was lost in the control seedlings.Differently to which,Pretreatment with exogenous melatonin can restore the rhythmic phenotype of the PRX-SO_2/3 rhythmic marker in treated seedlings under cold stress.