The Physiological Mechanisms Of The Salt Tolerance In A Wheat Stay-green Mutant, Tasg1

Soil salinization has been a global problem to restrict agricultural production today. Therefore, it is very important and significant to study the mechanism of salt tolerance in wheat and to breed the new salt tolerant wheat cultivars. Stay green mutant refers to the mutant that senescence delay. Researches showed that, senescence delay associated with drought resistance. Functional stay green mutant has the ability to resist drought stress. The wheat stay-green mutant, tasgl, was previously generated by chemical mutagenesis. Previous study has indicated that tasgl has higher drought resistance. In this study, we have determined the salt tolerance of the stay green mutant tasgl and researched the physiological mechanism about salt tolerance. Indexes determined include:photosynthesis parameters, fluorescence, Hill reaction activity, the activity of ATPase, relative water content, osmotic adjustment ability, compatible solutes contents, ions contents and anti-oxidant enzymes activities.Pn and Gs value decreased under salt stress, while Ci value increased. The changes of Pn, Gs and Ci were smaller in tasgl compare to WT. The photosynthetic apparatus of tasgl was less damaged. Fluorescence pramaters (Fv/Fm, ΦPS Ⅱ, qP) decreased in wheat leaves but the decrease in leaves of tasgl was smaller. This indicate that the PS Ⅱ reaction center was damaged, but the damage in tasgl leaves was lighter. NPQ value of wheat leaves increased and the increase in tasgl leaves was lager compare to WT. This indicate that tasgl has higher ability of thermal dissipation. Excessive excitation energy was dissipated by thermal radiation. Hill activity and ATPase activity decreased, but the decrease in tasgl was smaller. This indicated that protein complexes related with photosynthesis function is impaired in thylakoid. But the damage in tasgl was lighter.We can concluded that tasgl has stronger salt tolerance from higher photosynthesis in tasgl under salt stress. So we next determined the water status, the ion contents and anti-oxidation ability in tasgl and WT. The main results are as follows:(1) Under salt stress, tasgl could sustain higher osmotic adjustment and maintain a better water status compare to WT. Tasgl accumulated more content of compatible solutes, which could sustain higher osmotic adjustment and higher relative water content.(2) Salt stress increased Na+content and decreased K+content of wheat plants. Therefore, K+/Na+decreased and the ion homeostasis was destroyed. Compared to WT, tasgl had lower Na+content and higher K+content. Therefore, tasgl had higher K+/Na+and was less damaged by ion toxicity. tasgl could prevent the Na+transport from root to shoot. This is one of reasons that tasgl had lower Na+content in shoot.(3) Under salt stress, tasgl maintained higher activity of anti-oxidative enzymes and therefore had less hurt by oxidative stress. Salt stress induced oxidative stress. Salt stress caused increase in superoxide radical production, H2O2content, MDA content and membrane electrolyte leakage. But the increase amplitude in tasgl is smaller compare to WT. This may be associated to higher activities of antioxidant enzymes such as SOD, CAT, POD and APX in tasgl.From all the results above, we can come to the conculsion that tasgl has stronger salt tolerance compare to WT. The enhancement in salt tolerance in tasgl under salt stress might be relative to these aspects:Firstly, tasgl can accumulate a lot of osmoyltes and increase osmotic adjustment. Secondly, through enhancing the activity of antioxidant enzymes, the accumulation of ROS and peroxidant level of membrane lipids are mitigated, integrity and fluidity of thylakoid membrane are sustained; Thirdly, tasgl can sustain lower Na+content through preventing Na+to transport from root to shoot.