Barley is one of the mjor five crops cultivated worldwide for food and feed production. Barley belongs to the highly salt-tolerant crop species, but it suffers significant yield loss in large areas of marginal saline soils. Significant genetic variation in salt tolerance existing among barley germpl...
Barley is one of the mjor five crops cultivated worldwide for food and feed production. Barley belongs to the highly salt-tolerant crop species, but it suffers significant yield loss in large areas of marginal saline soils. Significant genetic variation in salt tolerance existing among barley germplasms has been the primary resources to exploit for the improvement of cultivated barley for salt tolerance. Thus, the objectives of this study were i) to explore diverse barely germplasms to obtain sources of salt tolerance and ii) to characterize physiological and molecular mechanisms underlying the tolerance of the selected germplasm. Four salt-tolerant barley varieties, Tunisia 34 (T34), Tunisia 45 (T45), Tunisia 52 (T52) and Tunisia 76 (T76) were seleced through the screening of over a thousand barley germplasms in a high saline field. In the follow-up laboratory study, T76 showed consistently high salt tolerance at germination and early seedling stages and was used for further characterization on the physiological and molecular mechanisms underlying the salt tolerance at the early seedling stage. Gwandongpi 41 (G41) was used as a susceptible variety. Exclusion of salt to shoot was the primary mechanism of salt tolerance in T76. In the shoot, Na+ content in T76 was as low as one third of that in G41, and the low Na+ was instrumental in maintaining the K+/Na+ ratio relatively lower. Protection from osmotic stress was also involved in salt tolerance of T76. Under the saline stress, ability to synthesize osmoprotectants was much higher in T76. Antioxidant systems including non-proteous compounds and antioxidant enzymes were also significantly contributed to salt tolerance in T76. T76 showed much higher DPPH radical scavenging activity, lower lipid peroxidation, and higher activites of antioxidant enzymes like Mn-SOD, CAT, and APX. Proteomic analysis revealed quantitative nature of tolerance and that proteins involved in photosynthesis, nitrogen and carbohydrate metabolism, and response to abiotic stresses are more frequently altered under salinity stress. Mechanisms contributing to salt tolerance of T76 included higher capacities to protect photosynthesis (apparatus, carboxylation and ATP synthesis), to regulate ABA synthesis and GA inactivation, and to increase osmoprotectant and antioxidant enzymes. Increased expression of HvNHX1 and HvHVP genes under saline stress in T76 confirmed that sequestration of Na+ in the cytosol to vacuole is also a part of the tolerance mechanism in T76. The involvement of Na+ sequestration was futher confirmed by the complementation of the mutant phenotype by heterologous expression of HvNHX1 in a yeast nhx mutant and the increased salt tolerance of HvNHX1?transgenic rice. Taken together, important contributors to the higher salt tolerance in T76 included the reduced transport of Na+ to the shoot, the increased enzymatic and nonenzymatic antioxidant capacity, the enhanced sequestration of Na+ to vacuole, and the integrated regulation of protein expression involved in several cellular functions, i.e., photosynthesis, stress response, nitrogen metabolism, nucleotide metabolism and antioxidant proteins. Also, involvement of Na+ sequestration in salt tolerance was convincingly demonstrated by the increased salt tolerance in HvNHX1-transgenic yeast nhx mutant and rice. Consequently, this study complemented our knowledge on salt tolerance of barley by extending our understanding on the mechanisms of salt tolerance at the physiological and molecular levels. Also, this study provided genetic materials and a practical approach to improve salt tolerance of crop plants by enhancing ability to transport Na+ to the vacuole that may lead to development of new crop varieties with improved adaptability to saline areas worldwilde.
Barley is one of the mjor five crops cultivated worldwide for food and feed production. Barley belongs to the highly salt-tolerant crop species, but it suffers significant yield loss in large areas of marginal saline soils. Significant genetic variation in salt tolerance existing among barley germplasms has been the primary resources to exploit for the improvement of cultivated barley for salt tolerance. Thus, the objectives of this study were i) to explore diverse barely germplasms to obtain sources of salt tolerance and ii) to characterize physiological and molecular mechanisms underlying the tolerance of the selected germplasm. Four salt-tolerant barley varieties, Tunisia 34 (T34), Tunisia 45 (T45), Tunisia 52 (T52) and Tunisia 76 (T76) were seleced through the screening of over a thousand barley germplasms in a high saline field. In the follow-up laboratory study, T76 showed consistently high salt tolerance at germination and early seedling stages and was used for further characterization on the physiological and molecular mechanisms underlying the salt tolerance at the early seedling stage. Gwandongpi 41 (G41) was used as a susceptible variety. Exclusion of salt to shoot was the primary mechanism of salt tolerance in T76. In the shoot, Na+ content in T76 was as low as one third of that in G41, and the low Na+ was instrumental in maintaining the K+/Na+ ratio relatively lower. Protection from osmotic stress was also involved in salt tolerance of T76. Under the saline stress, ability to synthesize osmoprotectants was much higher in T76. Antioxidant systems including non-proteous compounds and antioxidant enzymes were also significantly contributed to salt tolerance in T76. T76 showed much higher DPPH radical scavenging activity, lower lipid peroxidation, and higher activites of antioxidant enzymes like Mn-SOD, CAT, and APX. Proteomic analysis revealed quantitative nature of tolerance and that proteins involved in photosynthesis, nitrogen and carbohydrate metabolism, and response to abiotic stresses are more frequently altered under salinity stress. Mechanisms contributing to salt tolerance of T76 included higher capacities to protect photosynthesis (apparatus, carboxylation and ATP synthesis), to regulate ABA synthesis and GA inactivation, and to increase osmoprotectant and antioxidant enzymes. Increased expression of HvNHX1 and HvHVP genes under saline stress in T76 confirmed that sequestration of Na+ in the cytosol to vacuole is also a part of the tolerance mechanism in T76. The involvement of Na+ sequestration was futher confirmed by the complementation of the mutant phenotype by heterologous expression of HvNHX1 in a yeast nhx mutant and the increased salt tolerance of HvNHX1?transgenic rice. Taken together, important contributors to the higher salt tolerance in T76 included the reduced transport of Na+ to the shoot, the increased enzymatic and nonenzymatic antioxidant capacity, the enhanced sequestration of Na+ to vacuole, and the integrated regulation of protein expression involved in several cellular functions, i.e., photosynthesis, stress response, nitrogen metabolism, nucleotide metabolism and antioxidant proteins. Also, involvement of Na+ sequestration in salt tolerance was convincingly demonstrated by the increased salt tolerance in HvNHX1-transgenic yeast nhx mutant and rice. Consequently, this study complemented our knowledge on salt tolerance of barley by extending our understanding on the mechanisms of salt tolerance at the physiological and molecular levels. Also, this study provided genetic materials and a practical approach to improve salt tolerance of crop plants by enhancing ability to transport Na+ to the vacuole that may lead to development of new crop varieties with improved adaptability to saline areas worldwilde.
주제어
#Hordium vulgare NaCl K+/Na+ ratio Salt tolerance DPPH MDA Antioxidant enzymes Proteomic analysis 2-DE HvNHX1 Transgene
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