Water-deficit stress effects on pistil biochemistry and leaf physiology in cotton (Gossypium hirsutum, L.)

Abstract

Flowering in cotton (Gossypium hirsutum L.) is a sensitive stage to water-deficit stress, but the effects on metabolism are not well understood. The objective of this study was to monitor gas exchange responses of cotton plants under conditions of limited water supply and evaluate the effects on the carbohydrate concentrations and glutathione reductase levels in the cotton flower. Growth chamber experiments were conducted in 2008 and 2009, with normal day/night conditions of 32/24°C and optimum quantities of Hoagland's nutrient solution applied until flowering. Treatments were imposed at flowering and consisted of control (Control), where optimum quantities of water were applied, and water stress (WS) where 50% of optimum quantity of water was supplied. Water-deficit stress resulted in a significant decrease in leaf stomatal conductance. Leaf photosynthetic and respiration rates were similarly decreased compared to the control. Ovary and style water potential of water-stressed leaves were significantly higher compared to the water potential of water stressed leaves, indicating that cotton flowers are fairly resistant to changes in the water status of the plant. However, carbohydrate concentrations of water-stressed pistils (ovary and style) were significantly increased compared to the control and a similar pattern was observed in the levels of glutathione reductase of water-stressed pistils. In conclusion, water-deficit stress during flowering resulted in significant decreases in leaf gas exchange functions as well as leaf water potential. Cotton pistils appeared to be less sensitive since they were able to maintain water potential similar to the control under limited water supply and increase glutathione reductase levels. However, pistil carbohydrate metabolism was significantly affected resulting in accumulation of both hexose and sucrose indicating a perturbation in sucrose cleaving and hexose utilizing enzymes that could potentially have as a consequence a decrease in fertilization and seed set efficiency.