Physiological and biochemical behavior in soybean (Glycine max cv. Sambaiba) plants under water deficit

The experiment had the aimed at evaluating the effects of the progressive water deficit, as well as investigating the physiological and biochemical behavior in Glycine max cv. Sambaiba submitted to water restriction during the vegetative phase. The parameters that were measured are the leaf relative water content, plant dry matter, proline, total soluble carbohydrate, sucrose, reducing carbohydrates, free amino acids and total soluble proteins. The experimental design carried out was at entirely randomized factorial scheme, with 2 water regimes (stress and control) and 4 evaluation points (0, 2, 4 and 6 days). There was decrease in the leaf relative water content in plants under water deficit, however the total soluble carbohydrates, sucrose and reducing carbohydrates were increased at 40, 205.0, 19.2%, respectively, besides the accumulation of proline and free amino acids at 67 and 388.1%, respectively. Significant changes were shown on leaf relative water content, total soluble carbohydrates, sucrose and reducing carbohydrates with 2 days under water stress, indicating that the carbon metabolism is quickly modified and utilized as reserve source and membrane protector during the water deficit. Besides of this, the increase in free amino acids level occurred due to protein breakdown as consequence of the stress submitted to plants, however significant changes were not observed on the proline levels until the 4th day of water restriction. This fact reveals the inefficient osmotic adjustment and as consequence the high sensitivity of this species under conditions of water restriction.