Screening Of Alkali-tolerant Barley Germplasm At Germination Stage And Its Physiological Response To Alkali Stress

With the strong saline-alkaline resistance,barley is the excellent model plant for studying the plant tolerance under saline-alkaline stress.At present,researches on the effects of saline-alkaline stress on barley growth and development are mainly focused on salt stress,but there are few researches on alkali stress.The germination stage is the beginning of the whole life cycle of barley,and is less resistant to stress than other stages,which can directly affect the emergence rate of barley and is very important for the growth and development of barley.In this study,199 barley germplasm resources were comprehensively evaluated for alkali tolerance during the germination stage,and the morphological,physiological and germination characteristics of the selected materials with different alkali tolerance were studied,to find out the physiological mechanism of alkali tolerance of barley at germination stage,as well as to lay the foundation for stress-resistant cultivation of barley and breeding of new varieties with alkali tolerance.The main results are as follows:1.Alkali stress treatments with the concentration of 90 mmol/L（the molar ratio of Na HCO₃ to Na₂CO₃ is 9:1）was the suitable concentration for barley germplasm screening in the germination stage.199 barley germplasm materials were comprehensively evaluated and clustered into four categories:35 resistant varieties,102 moderately resistant varieties,36moderately susceptible varieties and 26 sensitive varieties.2.With the increase of alkali concentration,the germination potential,germination rate,germination index,vigor index,seedling length,root length,mobilization amount of stored substances and material utilization rate of Sichuan MS（resistant）and Qitai 9919（sensitive）all showed a downward trend,which showed that Sichuan MS was significantly higher than Qitai9919;The average germination time and dry weight of the remaining grains showed an upward trend,showing that Sichuan MS<Qitai 9919;Seedling dry weight,root dry weight,root conversion rate,seedling conversion rate and total conversion rate generally increased first and then decreased,reaching the highest value at 30 mmol/L.All germination characters generally showed that Sichuan MS was higher than Qitai 9919,in which the root dry weight,seedling conversion rate,root conversion rate and total conversion rate of Sichuan MS were higher than Qitai 9919 by 3.5%,6.6%,27.4%and 16%,respectively.3.With the increase of the concentration of alkali treatment,the activities of SOD,POD,CAT and enzymes related to ascorbic acid-glutathione cycle first increased and then decreased,and the overall activity of each enzyme was Sichuan MS>Qitai 9919,among which the activity of each enzyme of Sichuan MS reached the highest at 90mmol/L treatment,and the activity of each antioxidant enzyme of Qitai 9919 reached the highest at 60mmol/L treatment.The contents of MDA,DHA and ASA showed an increasing trend,and the overall performance was that Sichuan MS was less than Qitai 9919,and they all reached the highest value at120mmol/L treatment.The contents of GSH and GSSG increased first,then decreased and then increased,and the overall performance was Sichuan MS<Qitai 9919;The ratios of ASA/DHA and GSH/GSSG show a downward trend,with the decreasing range of Qitai 9919>Sichuan MS.4.With the germination time,the total starch content of Sichuan MS-CK,Qitai 9919-CK,Sichuan MS-T and Qitai 9919-T all showed a downward trend under alkali stress,showing that Qitai 9919-T>Sichuan MS-T>Sichuan MS-CK and Qitai 9919-CK;The contents of soluble sugar and soluble protein in the control and treatment of the two varieties first increased and then decreased.On the 1^st and 2^nd day of germination,the contents of soluble sugar and soluble protein in the treatment of the two varieties were lower than that in the control,while on the 4^thand 6^th day of germination,the contents of soluble sugar and soluble protein in the treatment of the two varieties were higher than that in the control,and with the germination time,the contents of soluble sugar and soluble protein in Qitai 9919-T were higher than that in Sichuan MS-T.5.With the germination time,the activities of substance metabolism-related enzymes,respiratory metabolism-related enzymes and the relative expression of genes of Sichuan MS-CK,Qitai 9919-CK,Sichuan MS-T and Qitai 9919-T showed a trend of first increasing and then decreasing under alkali stress,which showed that Sichuan MS-CK>Qitai 9919-CK>Sichuan MS-T>Qitai 9919-T.Except the activity of sucrose synthase and its relative gene expression reached the peak on the 2nd day of germination,the activity of other metabolism-related enzymes and their gene expression reached the peak on the 4^th day of germination.Under the control and treatment of the two varieties,the activities of enzymes related to the three respiratory metabolic pathways,namely,glycolysis（EMP）,tricarboxylic acid cycle（TCA）and pentose phosphate pathway（PPP）,and the relative expression levels of key enzyme genes all reached the peak on the fourth day of germination.