Sugar-Induced Tolerance to the Salt Stress in Maize Seedlings by Balancing Redox Homeostasis

Effects of exogenous glucose (Glc) and sucrose (Suc) on salt resistance, (glucose-6-phosphate dehydrogenase) G6PDH activity, ASA-GSH cycle and reactive oxygen species metabolism in maize leaves were studied. Seedings at two leaf stage were pretreated by 1/2 Hoagland nutrient solution with 0.5 mmol•L -1 Glc, Suc and mannitol for 3 days, some seedlings were left in normal nutrient solution and isotonic maninitol as control and permeability control respectively. Then the plants were cultured by 1/2 Hoagland solution at the concentration of 150 mmol•L -1 NaCl for 4 days or 6 days. The results showed that pretreatment with 0.5 mmol•L -1 glucose and sucrose for 3 days significantly decreased the thiobarbituric acid reactive substances (TBARS), H 2 O 2 contents and increased ASA, GSH contents, ASA/DHA, GSH/GSSG ratio and G6PDH activity in leaves of maize seedings under salt stress. We also found that sucrose pretreatment induced the increase of Ca 2+ -ATPase and maintained the balance of Ca 2+ contents under salt stress. In addition, compared with S treatment, isotonic mannitol pretreatment did not induce any changes of the physiological and biochemical indicators that meant it could not cause improvement of biological indicators of maize seedings. These results indicate that exogenous glucose and sucrose improved ASA-GSH cycle efficiency by participating in the pentose phosphate pathway (OPP), therefore enhanced antioxidant capacity and reduced the damage of active oxygen free radical, and the G6PDH activity induced by glucose and sucrose might serve as signal molecules and be involved in salt resistance of maize seedings.