Influence of Exogenously Applied Glycinebetaine on the Photosynthetic Capacity of Two Differently Adapted Wheat Cultivars under Salt Stress

Ameliorative effect of exogenously applied glycinebetaine (GB) on photosynthetic capacity of two wheat cultivars differing in salt tolerance grown under salt stress was assessed. Plants were grown under field conditions at 2.84, 15 dS/m in split-split plot design. Different levels of GB (no spray NS, 0.1% Tween 20 solution, 50 and 100 mM GB in 0.1% Tween 20 solution) were exogenously applied as a foliar spray to salt tolerant (S-24) and moderately salt sensitive (MH-97) wheat cultivars under saline and non-saline conditions. Salt stress reduced the photosynthetic capacity of both cultivars. Reduction in photosynthetic rate was primarily due to stomatal limitations. Cultivar S-24 excelled MH-97 under salt stress with respect to photosynthetic rate and leaf turgor potential. Salt-induced reduction in photosynthetic capacity was ameliorated by exogenous application of GB. High accumulation of GB mainly contributes to OA, which is one of the factors for improving photosynthetic capacity under salt stress. Better osmotic adjustment or plant water status due to GB application increased the stomatal conductance and thus favored higher CO2 fixation rate. The protective effect of GB on photosynthetic pigments and GB induced reduction in transpiration rate are additional factors which might have contributed to better growth of wheat cultivars under salt stress. However, cv. S-24 was higher in photosynthetic capacity and plant water status or osmotic adjustment than MH-97, which could explain the ability of the salt tolerant S-24 to show higher salt tolerance than the moderately sensitive MH-97.