Effect of Saline-Alkali Stress on Sugar Metabolism of Jujube Fruit

Sugar, an osmoregulatory substance used by plants to adapt to abiotic stresses such as drought and salinity, is one of the most important indexes of fruit quality. In this study, 0-150 mM saline-alkali solutions (NaCl:NaHCO3 = 3:1) were used to irrigate the roots of 10-year-old Junzao fruit trees during the growth period to explore the regulation mechanism of different concentrations of saline-alkali stress on sugar and reactive oxygen metabolism in jujube fruit at maturity. The results showed that under low stress (0-90 mM), the contents of sucrose, glucose, and fructose in the jujube fruit and the activities of sucrose phosphate synthase (SPS), sucrose synthase decomposition direction (SS-I), and sucrose synthase synthesis direction (SS-II) increased with increases in stress concentration, results that were consistent with the relative expression trends of the SPS and SS genes; however, the results were reversed under high concentrations (120 and 150 mM). The soluble acid invertase (S-AI) activity decreased with increases in stress concentration under low stress, and the results were reversed with high stress, which was consistent with the relative expression trends of the ZjcINV3, ZjnINV1, and ZjnINV3. Research regarding the response of antioxidant enzymes in fruits under saline-alkali stress showed that only the differences in peroxidase (POD) activity under saline-alkali stress were consistent with sugar accumulation; the proline (PRO), catalase (CAT) decreased and the malondialdehyde (MDA) superoxide dismutase (SOD) increased with increases in saline-alkali stress. These results indicate that the sugar metabolism and antioxidase jointly promote and regulate sugar accumulation in jujube fruits in a low saline-alkali environment.

Automated summary

This study investigates the effects of different concentrations of saline-alkali stress on sugar and reactive oxygen metabolism in jujube fruit. The results show that under low stress, the contents of sucrose, glucose, and fructose in the fruit increase with increasing stress concentration, along with the activities of related enzymes. However, under high concentrations of stress, the results are reversed. The activity of antioxidant enzymes is consistent with sugar accumulation under saline-alkali stress.