Effects Of Polyamine And Glycine Betaine On Cold Tolerance Of Centipede Grass And Drought Tolerance Of Bentgrass

Cold stress and drought stress are the major factors that inhibit turfgrass growth.In the Middle and Lower Reaches of the Yangtze River in China,warm-season turfgrass is mainly stressed by low temperature in winter,while cool-season turfgrass is mainly stressed by high temperature and drought in summer.Investigating the mechanisms of cold and drought tolerance in warm-season and cool-season turfgrass species are important for selecting and breeding cold-tolerant and drought-tolerant turfgrass cultivars,and utilizing chemical methods to enhance the survival from those abiotic stress in turfgrass is also important for turf management.In this study,eight centipede grass(Eremochloa ophiuroides(Munro.)Hack.)genotypes and six bentgrass(Agrostis stolonifera L.)genotypes were used in low temperature and drought stress study respectively.The morphology,physiological,and biochemical traits in leaves of these two turfgrass species were analyzed.The objectives of the research were to determine the genetic variations of cold tolerance in centipede grass,and the genetic variations of drought tolerance in bentgrass;to determine the major physiological and biochemical traits associated with osmotic adjustment,antioxidant enzyme system and stress tolerance in centipede grass and bentgrass;and to determine the effects of exogenous chemicals application on endogenous osmolytes accumulation and antioxidant defence system.These objectives were addressed by conducting four independent experiments.The main results of different experiments were summarized as following:1.The response of centipede grass leaf osmolytes content to low temperature before winter and its relationship with chilling injuryIn this study,the relationship between cold tolerance of eight different genotypes and leaf osmolytes content,including soluble sugar,proline,free putrescine,spermidine and spermine were performed using yield plot experiments during the winter chilling period from November to December of 2014 in Jurong Jiangsu.The results indicated that the leaf color(TQ)constantly decreased,while the electrolyte leakage(EL)and Malonaldehyde(MDA)content of leaves continually increased during chilling process before winter.Among eight genotypes,EL and MDA content of E02,E07,E09 and E10 were significantly lower than those of other four genotypes(P<0.05).However,the content of soluble sugar,proline,spermidine and spermine was significantly higher than those of other genotypes(P<0.05).There was positive correlation between EL and MDA content(r=0.74,P<0.05),while there were significant negative correlations between EL and SS,Pro,Spm,Spd(r=-0.83,-0.85,-0.88,-0.91,respectively,P<0.01).There were also significant negative correlations between MDA and SS,Pro,Spm,Spd content(r=-0.68,-0.66,-0.83,-0.72,respectively)(P<0.05).Therefore,those four osmolytes,soluble sugar,proline,spermidine,spermine in leaves play important roles in enhancing cold tolerance for centipede grass.2.Foliar spraying putrescine and spermidine increased antioxidant enzyme activities and osmolytes content in centipede grass and improved its cold toleranceIn this study,the effect of exogenous putrescine(Put)and spermidine(Spd)on the leaves electrolyte leakage(EL),MDA content,antioxidant enzyme activities and osmolytes content in centipede grass under low temperature were investigated.The results showed that the application of exogenous putrescine and spermidine with a concentration of 0.1mM significantly decreased the leaves electrolyte leakage(EL)(8.11～16.64%and 11.93～25.55%,respectively),and MDA content(1.71～6.39 μmol·g-1 FW and 3.57～10.54 μmol·g-1 FW,respectively),while significantly increased the antioxidant enzyme activities including SOD(475.3～1237.2 U·g-1 DW and 374.6～1461.4 U·g-1 DW,respectively),POD(35.6～223.1 U·g-1 DW and 147.6～273.7U·g-1 DW,respectively),APX(3.6～6.3 U·g-1 DW and 6.0～9.7 U·g-1 DW,respectively),and CAT(289.1～1224 U·g-1 DW and 900.4～3017.8 U·g-1 DW,respectively),and also increased the osmolytes content such as soluble sugar(7.3～37.9%and 27.3～89.3%,respectively),proline(10.7%and 13.8%,respectively),putrescine(13.3～85.5%and 9.1～88.8%,respectively),spermidine(8.6～39.3%and 18.7～53.6%,respectively)and spermine(7.6～19.5%and 12.6～51.7%,respectively)during the low temperature stress.This study indicated that the application of exogenous polyamines could increase the antioxidant enzyme activities as well as the osmolytes content,and decrease the stress damage on the centipede grass during low temperature stress.3.Significant correlation between osmoregulants and drought tolerance among different bentgrass genotypesA wild type cultivar of bentgrass[Agrostis stolonifera(Penncross)],a transgenic line of creeping bentgrass(SAGIPT41),and four hybrid bentgrass lines[Agrostis capillaris·Agrostis stolonifera(ColxCr14,ColxCr190,ColxCr481,and ColxCr679)]were used in this experiment to analyze the differences of drought stress by withholding irrigation for 17 days in growth chambers.ColxCr14,ColxCr190,and SAGIPT41 showed superior drought tolerance,as manifested by higher TQ and leaf relative water content(RWC),as well as OA than ’Penncross’,ColxCr679,and ColxCr481 under drought stress.SAGIPT41 leaves accumulated higher content of soluble sugars(glucose,sucrose,and fructose),proline,glycine betaine(GB),and spermine;ColxCr190 had higher content of soluble sugars and spermidine;and ColxCr14 accumulated more soluble sugars and GB,compared with the three drought-sensitive genotypes.The osmolytes significantly correlated with OA and superior drought tolerance could be used as biomarkers to select for drought-tolerant germplasm of bentgrass and other cool-season turfgrass species.4.Foliar spraying of glycine betaine and spermidine on bentgrass significantly enhanced osmotic adjustment and antioxidant defense under drought stressThe endogenous content of GB and Spd increased significantly after exogenous application of GB and Spd,and the effects of GB were more significant(P<0.05).Compared with control,spraying exogenous GB and Spd significantly increased TQ and RWC of bentgrass(P<0.05),and decreased the content of EL and MDA.Exogenous Spd only promoted the accumulation of Spd in leaves,but had no significant effect on OA and GB(P>0.05).In addition,the activities of SOD,POD,APX and CAT were significantly increased by spraying exogenous GB and Spd(P<0.05).The results showed that exogenous GB and Spd could improve the drought tolerance of bentgrass,but the mechanism was different.Exogenous GB could improve the OA value of leaf cells by increasing the content of endogenous GB,and improve the activity of APX and antioxidant enzyme system.Finally the drought resistance of bentgrass was significantly improved.Spraying exogenous Spd had no significant effects on the OA value’ of bentgrass,but it significantly improved CAT activities.The results showed that the activity of antioxidant enzymes and the drought tolerance of bentgrass were improved after exogenous glycine betaine and spermidine application.In summary,the results showed that the contents of SS,Pro,Spd,Spm and GB were negatively correlated with the content of EL and MDA(P<0.05),and positively correlated with the resistance of centipede grass and bentgrass(P<0.05).During low temperature stress,the accumulation of SS,Pro,Spd and Spm in the leaf cells of the cold-tolerant genotypes was 1.76,1.75,3.51 and 12.1 times that of the cold-tolerant genotypes in centipede grass under,respectively.The content of SS,Pro,Spd,Spm and GB in the leaves of drought tolerant genotypes was significantly higher than those of the drought sensitive genotypes under drought stress(P<0.05).Under low temperature or drought stress,the contents of SS,Pro,Spd,Spm and GB enhanced the stress resistance of the centipede grass and bentgrass.Foliar spraying of Spd,Put and GB could increase the content of SS,Pro,Put,Spd,Spm and GB in the centipede grass and bentgrass under low temperature and drought stress,regulated cell OA,and maintained the water potential of the turfgrasses.In addition,the activities of SOD,POD,APX and CAT were significantly increased by spraying exogenous Spd,Put and GB,and the cold tolerance and drought tolerance of turfgrass were significantly improved(P<0.05).SS,Pro,Spd,Spm and GB could not only be used as the index substance to measure the cold tolerance and the drought tolerance of centipede grass and bentgrass,but also as the effective exogenous regulator to improve the corresponding stress tolerance of the two turfgrass.These were of great significance to the stress-resistant breeding and the management of stress-resistant turfgrass.