Influence of Exogenous Glycine Betaine on Gas Exchange and Biomass Production in Sunflower (Helianthus annuus L.) under Water Limited Conditions

This study investigated whether the exogenous application of glycine betaine (GB) could alleviate the adverse effects of water deficit on sunflower. Two sunflower lines, Gulshan-98 and Suncross, were subjected to water deficit at the vegetative or the reproductive stages of plant growth. Three levels (0, 50 and 100 mmol l^?1) of GB were applied as a pre-sowing seed treatment or as a foliar spray at the time of initiation of water deficit at the vegetative or reproductive stages. Foliar application of GB at the time of initiation of water deficit treatments showed a marginal increase in shoot biomass in drought-stressed plants. Exogenously supplied GB as a foliar spray also showed a positive role in reducing the effects of water deficit on net CO₂ assimilation rate, transpiration rate and sub-stomatal CO₂ concentration in both sunflower lines. Pre-sowing seed treatment with GB had no effects on the above-mentioned physiological and growth attributes in both normally irrigated and drought-stressed plants. Taken together, foliar application of GB increased net CO₂ assimilation rate which in turn showed a slight increase in growth of water-stressed plants but this increase was not related to stomatal regulation.