| Wheat is the most widely planted crop on the earth and it is also the main food source in most parts of the world,providing a lot of carbohydrates and proteins for human beings.Although the production of food crops such as wheat has been greatly increased in recent years,the demand for food is still enormous because of the rapid population growth.In order to guarantee food security,the crop yield must be further improved.And enhancing the per unit area yield is more effective and sustainable than increasing arable land.In addition,crop production has been raised to a high level through the methods of resistance improvement and morphological breeding.However,it has become an important method to increase crop yield by cultivating new crop varieties which can delay leaf senescence,prolong effective photosynthesis and thus providing sufficient photosynthetic products for grain filling.In this study,the effects of spike shading on photosynthesis,biochemical indexes and agronomic traits of stay-green wheat and non-stay-green wheat after heading were investigated,aiming to further clarifying the contribution of spike photosynthesis to yield formation and the compensation mechanism of leaves in different types of wheat to shading stress.Furthermore,transcriptome sequencing was used to explore the changes of gene expression in the process of leaf senescence in both stay-green wheat and non-stay-green wheat,so as to identify the metabolic pathways and key genes related to delaying leaf senescence,lead to a better understanding of the regulation mechanism of saty green and promote the application of stay green trait in production practice.The main results of this study are as follows:1.The stay-green wheat cultivar CN12 and the non-stay-green wheat cultivar CN19 were selected to investigate the effect of spike shading on different types of wheat.After heading,the spike shading treatment was carried out.The photosynthetic and biochemical parameters were measured at 0,15 and 30 days after heading,respectively.And the final yield index were investigated after grain maturity.The results are outlined below:(1)CN12 is a functional stay-green wheat cultivar,which can delay leaf senescence and maintain high Pn in the later growth period under the condition of both spike shading and no shading.Besides,the negative effect of spike shading on grain yield of stay-green genotype was lower than that of non-stay-green genotype.Therefore,The flag leaves of functional stay-green genotype had a buffering or compensating effect on spike photosynthesis.(2)The response of CN12 to shading was related to the excitation capture efficiency in open PSII reaction centers,photosynthetic efficiency,antioxidant enzyme activity and membrane lipid peroxidation.Further analysis showed that under spike shading,CN12 enhance the photosynthetic capacity by regulating the efficiency of excitation capture in open PSII reaction centers and regulate the reactive oxygen species concentration by changing antioxidant enzyme activity,indicating that functional stay-green wheat could adjust actively under environmental stress and reduce the negative effect of abiotic stress.2.In the previous research,wheat cultivar CN17 has been used for study of delaying leaf senescence,and the hypothesis that chloroplast ultrastructure regeneration may be related to delaying leaf senescence has been proposed.To identify the metabolic pathways and key genes related to chloroplast structural stability and investigate the change of gene expression between genotypes during leaf senescence,stay-green wheat cultivar CN17 and non-stay-green wheat cultivar CN19 were chosed to perform transcriptome sequencing both before and after the onset of leaf senescence,and determine the photosynthetic,biochemical parameters as well as the final yield index.The results are outlined below:(1)CN17 is a functional stay-green genotype,exhibiting a higher chlorophyll content,photosynthetic capacity,antioxidant enzyme activity and yield than the control genotype.(2)The number of genes differentially expressed between CN17 and CN19 after leaf senescence was higher than that before leaf senescence.Meanwhile,the number of genes differentially expressed during leaf senescence in CN17 was significantly lower than that in CN19.(3)The analysis of gene differential expression revealed that there were significant differences in some genes associated with leaf senescence,such as senescence-associated genes,chlorophyll synthesis genes,light-harvesting chlorophyll protein complex genes and antioxidant enzyme genes,between CN17 and CN19 in the process of leaf senescence.(4)The down-regulation of senescence-associated genes in CN17 reduced the degradation of chloroplast proteins and photosynthetic proteins.The up-regulation of key chlorophyll synthesis genes(Traes CS2B01G447300)and related genes may play a key role in maintaining high chlorophyll content.Meanwhile,the upregulation of Por genes,Lhc genes and antioxidant enzyme genes(especially catalase genes)may act as a safeguard by offering a protection mechanism for functional stay-green genotype,which reduced membrane lipid peroxidation damage caused by reactive oxygen species,maintained the integrity of photosynthetic apparatus,and enabled functional stay-green wheat to delay leaf senescence and maintain high photosynthetic activity in the later growth period,thus providing continuous photosynthetic products for developing seeds.In summary,functional stay-green wheat cultivar CN12,CN17 and non-stay-green wheat cultivar CN19 all exhibit high yield and disease resistance,however they are different types of varieties.Compared with the CN19,CN12 and CN17 can delay leaf senescence and maintain higher photosynthetic activity in the late growth period.The stay green trait may be mainly regulated by chlorophyll synthesis genes,light-harvesting chlorophyll protein complex genes,antioxidant enzyme genes and senescence-associated genes.In addition,the functional stay-green wheat cultivar exhibits higher resistance to the abiotic stress of spike shading,and can actively adapt to environment by regulating photosynthetic performance and antioxidant enzyme activity,so as to reduce the impact of environmental stress on its yield. |
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