The Function And Gene Exprewioii Analysis Of Chlorophyllase And Pheophytinase In Wheat

Chlorophyll is a key pigment molecules in harvesting light energy for photosynthesis. During leaf senescence, chlorophyll continually degrades, at the same time photosynthetic capacity also gradually decreases, so yield and quality of crop have a directly effect. At present known there are two pathways for chlorophyll degradation: the removal of phytol befor a Mg atom from Chl a by chlorophyllase (CLH), another way is removing a Mg atom before the phytol group from Chl a by Pheophytinase (PPH), but the chlorophyll degradation pathway has no reported in wheat leaf. Based on this, the study used 16 wheat varieties as tested materials, and measured senescence related traits (chlorophyll content and green leaf area duration) after anthesis of wheat stem flag leaf under normal irrigation and drought stress conditions in 2013 and 2014, the purpose was to select stay-green type (delay senescence) and non-stay-green type (early senescence) wheat varieties. Then using transmission electron microscopy further confirmed at the cellular level. Finally, we analysed the enzyme activities and gene expression levels of the key enzymes of chlorophyll degradation at different senescence stages of different stay-green types wheat leaves, the aim was to explore chlorophyll degradation pathway of wheat leaf, and to provide information for reveal the chlorophyll degradation mechanism. The results are as follows:Chlorophyll content and green leaf area duration changing after anthesis were simulated by Gompertz curve. According to classify method, based on the time of beginning to senescence, the maximum rate of senescence, the time of the maximum rate and the time of ending to senescence, 16 wheat varieties were divided into three types: the stay-green type, the intermediate type and the non-stay-green type. TaiNong 18 belongs to stay-green wheat and Chang 6135 belonged to non-stay-green wheat under four environmental conditions in 2013 and 2014.Compared with TaiNong 18 and Chang 6135, TaiNong 18 had higher chlorophyll content, slower degradation rate of chloroplast structure, longer green leaf area duration and longer the effective photosynthesis, so it may be the main reason of higher grain of TaiNong 18.The decrease of chlorophyll content was consistent with the increase of CLH activity and PPH activity in wheat leaf. The time of maximum activity of CLH and PPH in TaiNong 18 were later than Chang 6135, and between TaiNong 18 and Chang 6135, the activity of CLH were no significant difference, but the activity of PPH had very significant difference, TaiNong 18 was far less than Chang 6135. Furthermore, the activity of PPH had two peaks, and the second peak is larger than the first. The activity of CLH had only one peak, and the time was consistent with the time of the first peak of PPH. The activity of PPH were larger than CLH in each stage of senescence. These results indicated that PPH plays a key role during the entire senescence process of wheat leaf, but CLH had only a part of the function.After dark treatment of TaiNong 18 and Chang 6135, TaCLH and TaPPH were induced, and the expression levels of TαPPH was much higher than TαCLH. Once again proved that PPH plays a key role for chlorophyll degradation in wheat leaf.