Interactive Effects of Sudden and Gradual Drought Stress and Foliar-applied Glycinebetaine on Growth, Water Relations, Osmolyte Accumulation and Antioxidant Defence Systemin Two Maize Cultivars Differing in Drought Tolerance

Influence of sudden and gradual drought stress (DS) and foliar-applied glycinebetaine (GB) on growth, water relations, osmolyte accumulation and antioxidant defence system were investigated in the plants of two maize (Zea mays L.) cultivars, that is, drought-tolerant Shaandan 9 (S-9) and drought-sensitive Shaandan 911 (S-911). Sudden DS caused less accumulation of GB and free proline, but a more accumulation of malondialdehyde (MDA), which resulted in a greater reduction in leaf relative water content (RWC) and dry matter (DM) in both cultivars compared with the gradual DS. Exogenous GB application caused a rise in DM, RWC, contents of GB and free proline as well as the activities of SOD, CAT and POD along with a decline in MDA content to various extent in both cultivars under both types of DS. A more pronounced effectiveness of GB application was observed in S-911 than that in S-9 under the same type of DS. It seemed that the more serious damage of DS was on maize plants, and the better positive role of GB was observed in terms of mitigating the adverse effects of DS. From this study, it was possible to propose that hardening for drought resistance by gradual DS treatment and GB application are effective to make plants robust to thrive under water-deficit conditions.