Studies On Glycine Betaine Enhanced The Tolerance Of Tobacco To Heat Stress

As sessile organisms, plants are continuously exposed to biotic and abiotic stressconditions during their whole life cycles. High temperature which affects the growthand the production of crops is a common abiotic stress during summer. Over time,plants have evolved mechanisms to overcome environmental stresses. Onemechanism is the accumulation of compatible solutes such as glycinebetaine （GB）.GB is one of the organic compatible solutes that can accumulate rapidly in manyplants under salinity stress, drought and low temperature, and enhanced the toleranceto adverse conditions. In this study, the BADH and BADH transgenic tobacco wereused to elucidate the affects of GB on tobacco under high temperature duringgermination and seedling growth. Additionally, GB was exogenously applied tofurther investigate the role of GB in the enhancement of the tolerance to hightemperature. The main results are showed as follow:（1） Heat Stress reduce tobacco photosynthetic rate. Wild-type tobaccophotosynthetic rate, apparent quantum efficiency, the decreased more significantly, L4strains betaine content, net photosynthetic rate and decrease in quantum efficiencytable minimum. Heat stress transgenic BADH tobacco maintain higher photosyntheticrates, increased tolerance to high temperature photosynthesis.（2） chlorophyll fluorescence analysis showed that: transgenic BADH PSIItobacco increased tolerance to high temperature stress. Exogenous Betaine alsoapplied to improve the tobacco leaf photosynthesis and PSII reaction centers ofresistance to high temperature.（3） under high temperature stress tobacco vivo H₂O₂, O₂-accumulation wassignificantly increased in vivo transgenic BADH tobacco less accumulation ofreactive oxygen species. Transgenic BADH under high temperature stress by maintaining higher tobacco antioxidant activity increased reactive oxygen speciesscavenging capacity, reducing reactive oxygen species damage to photosyntheticapparatus.（4） high-temperature-induced HSP70accumulation in leaves of transgenicBADH tobacco HSP70content than wild-type tobacco; exogenous betaine appliedHSP70in tobacco leaves is not applied betaine content than tobacco.（5） Cacl₂pretreatment increased exogenous Ca2+content of tobacco in vivo;exogenous Cacl₂pretreatment increased tobacco photosynthesis and fluorescencerate.（6） exogenous Cacl₂pretreatment reduced the tobacco vivo H₂O₂, O₂-content,improve the activity of antioxidant enzymes in tobacco.（7） Heat Stress makes when betaine calmodulin, heat shock protein surge; Afteradding EGTA, calmodulin, heat shock protein expression was significantly reducedThese results above suggest that exogenous betaine and BADH genes increasedtolerance to high temperature tobacco exogenous Cacl₂pretreatment can also increaseresistance to high temperature of tobacco. Heat stress when exogenous betaine andBADH genes significantly increased tobacco calcium ion concentration, and makescalmodulin, heat shock protein surge; adding EGTA after calmodulin, heat shockprotein expression was significantly reduced, betaine may influence the calcium ioncontent of tobacco to regulate calcium signaling pathway, thereby regulating theexpression of resistance genes to enhance the heat resistance of the tobacco.