Comparison Of Physiological Responses Of Two Wheat Cultivars To Saline-alkali Stress And Screening Of Differential MicroRNA

With the increase of population and the deterioration of natural environment,soil salinization has become an increasingly serious global problem.According to statistics,about 7%of the world’s land area（more than 900 million hectares）is threatened by salinization,and there are no effective measures to control its spread.China also has 100 million hectares of saline-alkali land.Therefore,soil salinization is a widespread abiotic stress source and has become a major limiting factor of agricultural crop production worldwide.In this study,to explore the mechanism of wheat response to salinity-alkalinity stress difference,the differential effects of salt-alkali stress on QM6（salt-alkali tolerant genotype）and MS0308（salt-alkali sensitive genotype）were investigated,based on the analysis of morphological indexes,photosynthetic characteristics,active oxygen metabolism and miRNAs of wheat seedlings.The main results were as follows:1.With the increase of salt-alkali concentration,the length of cauline leaf,fresh weight of cauline leaf,dry weight of cauline leaf,root length,fresh weight of root and dry weight of seedlings of QM6 and MS0308 showed a decreasing trend.However,with the increase of salt-alkali concentration,the morphological indexes of QM6seedlings decreased slightly and still maintained a relatively good growth trend.2.As the salinity increases,the chlorophyll content（SPAD）,net photosynthetic rate（Pn）,stomatal conductance（Gs）,transpiration rate（Tr）,photosynthetic electron transfer efficiency（ETR）,actual photoquantum yield（φPSII）,non-photochemical quenching coefficient（q P）and PSII maximum photoquantum yield（Fv/Fm）of QM6and MS0308 were all decreased,while the intercellular CO₂（Ci）concentration increased.And the photosynthetic performance was decreased and photosynthetic electron transport activity was inhibited under salt-alkali stress.Moreover,the reduction of QM6 is smaller.These results indicate that saline-alkali stress destroys photosynthetic system,weakens light energy utilization and inhibits photosynthetic electron transport activity Moreover,the more saline-alkali tolerant varieties were,the less damage degree of photosynthetic apparatus was,which also improved their ability to resist saline-alkali stress to a certain extent.3.The activities of superoxide dismutase（SOD）,peroxidase（POD）,catalase（CAT）,ascorbate photooxidase（APX）and glutathione reductase（GR）in wheat seedling roots decreased with the increase of salt and alkali concentration.However,deoxyascorbic acid（As A）content,oxidized ascorbic acid（DHA）content,oxidized glutathione（GSSG）content,reduced glutathione（GSH）content,As A/DHA and GSH/GSSG ratio increased.And then the superoxide ion（O₂^-）production rate and hydrogen peroxide（H₂O₂）content increased and exceeded the threshold,leading to membrane lipid peroxidation and increase in content of malondialdehyde（MDA）,which inhibited root activity.Moreover,the effects of salt-alkali stress on QM6 were significantly reduced.These results indicated that there were significant differences in antioxidant enzyme system and ASA-GSH cycle in different salt-tolerant varieties,which may be the physiological mechanism of wheat seedlings with different salt-tolerant types coping with peroxide damage caused by salt-alkali stress.4.In this study,a total of 11,368 miRNAs were detected from 6 samples of the two varieties,including 106 conservative miRNAs and 11,262 non-conservative miRNAs.Compared with the control group,a total of 56 miRNAs were differentially expressed under salt-alkali stress,37 were significantly up-regulated and 19 were significantly down-regulated.KEGG pathway analysis showed that four target genes in treatment groups were involved in five pathways including fatty acid metabolism,phenylalanine metabolism,plant hormone signal transduction,arginine and proline metabolism,and tryptophan metabolism.Under saline-alkali stress,four miRNAs（tae-miR 9653b,tae-miR 5384-3p,tae-miR 9777,and tae-miR 531）had the same trend,and one（tae-miR 171）had the opposite trend.MS0308 was specifically expressed by one miRNA（tae-miR 159）.One miRNA（tae-miR 159）was specifically expressed in MS0308,and four miRNAs（tae-miR 7757-5b,tae-miR 4083p,tae-miR164,and tae-miR9662）were specifically expressed in QM6.In conclusion,these miRNAs differentially expressed in wheat varieties with different salt-alkali tolerance may be an important factor in the formation of different salt-alkali tolerance.In conclusion,this study measured and analyzed the physiological responses of different salt-alkali tolerant wheat varieties under salt-alkali stress,and identified and analyzed the mirnas and their target genes involved in salt-alkali stress,as well as the differentially expressed mirnas of different varieties.The results will provide a basis for analyzing the mechanism of salt and alkali tolerance in wheat.