The physiological and metabolic changes in sugar beet seedlings under different levels of salt stress
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Salinity stress is a major limitation to global crop production. Sugar beet, one of the world’s leading sugar crops, has stronger salt tolerant characteristics than other crops. To investigate the response to different levels of salt stress, sugar beet was grown hydroponically under 3 (control), 70, 140, 210 and 280 mM NaCl conditions. We found no differences in dry weight of the aerial part and leaf area between 70 mM NaCl and control conditions, although dry weight of the root and whole plant treated with 70 mM NaCl was lower than control seedlings. As salt concentrations increased, degree of growth arrest became obvious In addition, under salt stress, the highest concentrations of Na+ and Cl− were detected in the tissue of petioles and old leaves. N and K contents in the tissue of leave, petiole and root decreased rapidly with the increase of NaCl concentrations. P content showed an increasing pattern in these tissues. The activities of antioxidant enzymes such as superoxide dismutase, catalase, ascorbate peroxidase and glutathione peroxidase showed increasing patterns with increase in salt concentrations. Moreover, osmoprotectants such as free amino acids and betaine increased in concentration as the external salinity increased. Two organic acids (malate and citrate) involved in tricarboxylic acid (TCA)-cycle exhibited increasing contents under salt stress. Lastly, we found that Rubisco activity was inhibited under salt stress. The activity of NADP-malic enzyme, NADP-malate dehydrogenase and phosphoenolpyruvate carboxylase showed a trend that first increased and then decreased. Their activities were highest with salinity at 140 mM NaCl. Our study has contributed to the understanding of the sugar beet physiological and metabolic response mechanisms under different degrees of salt stress.
KeywordsSalt stress Reactive oxygen species Osmotic stress Photosynthesis Sugar beet
Lisa David from University of Florida is acknowledged for critical reading of the manuscript. This work was supported by the Project of Natural Science Foundation of Heilongjiang province (project no. C2016048: A preliminary study on the molecular drought tolerance mechanism of T510 strains of sugar beet); Project of international Cooperation (project no. 2010DFAN31530: Drought resistance, salt tolerance breeding, and cultivation for energy beet); Project of National Natural Science Foundation of China (project no. 31271779: Excavation of germplasm resources of higher salt tolerance and osmotic regulation mechanism in sugar beet); Youth Science Funds of Heilongjiang University (Project no QL201511: A preliminary study on salt tolerance mechanism of T510 strains of sugar beet).
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