Physiological Responses And Molecular Mechanism Of Zoysiagrass To Temperature Stress

Temperature as a drive force of biological functions affects plant's transpiration,absorption,water potential,nearly all enzymatic reations,dormancy and growth.Thetemperature range of growth in turfgrass is narrow.The suitable temperature range of growthfor cold-season turfgrass is 15～24℃,while it is 26～32℃for warm-season turfgrass.Whenit exceeds the suitable temperature range,the natual growth and health of turfgrass will beinfluenced.Studying on the cold resistance and heat tolerance of turfgrass is a hot issue.Somestudies on the physiobiochemical mechanism of the resistance in turfgrass have been carriedout,however few information is available in the molecular mechanism of its resistance inChina.The study is to detect the physiological responses and molecular adaptationmechanism of warm-season turfgrass to temperature stress.Two warm-type turfgrass species,the most widely planted,such as Zoysia matrella (L.)merr.and Zoysia japonica steud.,were used for the experiment to detect the physiologicalresponses to low and high temperature stress.The results showed that the contents of solublesugar,soluble protein,proline,were all increased,but the increasing changes in the contentsof soluble sugar and proline were higher in Z.matrella than in Z.japonica under the sametemperature stress.Superoxide dismutase (SOD),peroxidase (POD)and catalase (CAT),which function is clearing active oxygen,are the system of protective enzymes in cellmembrane.The study showed that the activities of SOD,POD and CAT were all builded up inthe two turfgrass species under the low and high temperature stresses.But the increased extent ofSOD and CAT in Z.matrella was much higher than that in Z.japonica,however Z.japonica showedhigher activity of POD than Z.matrella under the temperature stress.Malondialdehyde (MDA)isone major production of membrane lipid peroxidation.Its accumulation is physiologicalindicator of active oxygen toxicity.It was found that the content of MDA was insignificantlyincreased under the high temperature stress,but it was significantly enhanced under the lowtemperature stress in the two turfgrass species.The increasing extent of MDA content wasmuch higher in Z.matrella than that in Z.japonica under the low temperature stress.Photosynthetic pigments not only affect the colour and luster of turfgrass but also affect itsphotosynthesis.It was also found that low and high temperature treatment caused decreases in carotenoid (Car),chlorophyll a (Chla)and chlorophyll b (Chlb)contents and changes inChla/Chlb.However,the two turfgrass species responded to the temperature stressdifferently.The decreasing extent of the pigments was higher in Z.japonica under thetemperature treatment.Endogenous hormones play an important role on the plant growth.Thestudy showed that the content of ABA was increased when exposed to temperature treatment,and the increased extent was much higher under 40℃treatment than under 0℃or10℃treatment in the two turfgrass species.The increased degree of ABA in Z.matrella wasmuch higher than that in Z.japonica under the same temperature treatment.It maitainedrelatively high contents of promoting hormones in the two turf grass species under the hightemperature treatment,but reverse was true in the low temperature treatment.As far as thebalance of endogenous hormones was concerned,the ratio of inhibiting hormones topromoting hormones was increased in the two turfgrass species under the temperaturetreatment.According to the results obtained from analyzing the resistance physiological indexes,itindicated that the two turfgrass species performed stronger resistibility under the hightemperature stress than under the low temperatue stress and Z.matrella showed the strongerresistance than Z.japonica under the same temperature stress.In this article,the warm season turfgrass,Z.matrella,which showed stronger resistancein the experiment of resistance physiology,was studied using two-dimensional gelelectrophoresis(2-DE),mass spectrometry(MS),and bioinformatics analyses to explore thedifferentially expressed proteins of the turfgrass under low temperature and high temperaturetreatments.The result indicated that there were 35 potein spots which showed differentexpression partterns after the the different treatments.Of these,26 proteins were successfullyidentified with the aid of Q-TOF MS and bioinformatics.These proteins were involved insignal transduction,metabolism,stress resistance,protein synthesis and degradation,celltransportation capacity and embryo development.There were 20 proteins identified by Q-TOFMS,of which 4 proteins were ribulose bisphosphate carboxylase large subunit,under the lowtemperature treatment.On the one hand,some of these proteins strengthened signaltransduction,active oxygen scavenging and protein defencing,which were attributed to havethe strong resistant ability in Z.matrella,on the other hand,some other proteins,which was down-regulated,the respiration was strengthen firstly and then weaken,photosythesis wasdecreased,protein degraded,and transportatio ability of cell organ reduced in Z.matrella,inturn caused the plant growth trouble.There were 19 proteins successfully identified byQ-TOF MS,of which 3 proteins were ribulose bisphosphate carboxylase large subunit,underthe high temperature treatment.These proteins strengthened signal identification,transmembrane signal transduction,photosythesis,respiration,secondary metabolism,activeoxygen scavenging,protein defencing and protein synthesis,and led to the strong resistibilityof Z.matrella under the high temperature treatment.Besides that,the relative abundance ofZLL/PNH homologous protein decreased and the decreasing extent was increased with thetime prolonged under the low temperature treatment.The similar tendency was also foundunder the high temperature stress.These suggested that it was unfavorable for the main stemmeristematic tissue development and growth either under the high temperatue stress or underthe low temperatue stress.Further,an investigation was conducted to detect the related gene expression profiles in Z.matrella exposed to high temperature stress using suppression subtractive hybridization(SSH)method.A total of 35 ESTs from SSH-cDNA library were sequenced,and all of thesequences of inserted fragments were analyzed with the aid of bioinformatics.It obtained 26different functionally known genes.These genes were sorted into four groups such asmetabolism,gene expression regulation and signal transduction,stress resistance and proteinsynthesis.The expressions in genes of NADP-dependent malic protein,ribosomal protein S 1and catalase,which respectively involved in metabolism,protein synthesis and active oxygenscavenging,were enhanced under the high temperature stress.This result is consistent to thoseof differential proteomics research,and in turn further proved that the resistance wasstrengthened by improving metabolism,protein synthesis and the ability to scavenge activeoxygen in Z.matrella under high temperature stress.Finally,the author also discussed why alot of strengthen expression genes,which were identified in the experiment,were differentfrom outcomes of differential proteomics research in this paper.