Effect of high night temperatures during anthesis on cotton (Gossypium hirsutum L.) pistil and leaf physiology and biochemistry

Abstract

Flowering in cotton is a sensitive stage to heat stress but the effects of high night temperatures on cotton's pistil metabolism are not well understood. The objective of this study was to evaluate the effects of high night temperatures on the carbohydrate, glutathione reductase and free polyamine content of the cotton pistil and its subtending leaf. Growth chamber experiments were conducted using cotton ('Gossypium hirsutum' L.) cultivar ST5288B2F. Treatments consisted of normal day/night (32/24 degreesC) and high night temperatures (32/30 degreesC) for two weeks at flowering. Pistil glucose and sucrose concentrations were significantly increased under conditions of high night temperatures and the same pattern was observed for starch concentrations. However, even though leaf respiration increased, only heat-stressed leaf starch levels were significantly lower compared to the control. In contrast, leaf glutathione reductase was significantly increased under high night temperatures while pistil glutathione reductase remained similar under both control and stress conditions. High night temperatures significantly increased leaf and pistil putrescine content, but had no effect on leaf and pistil spermidine content. Spermine content was significantly increased in the pistil but not in the leaf. In conclusion, leaf antioxidant metabolism appeared to be more efficient in protecting leaf carbohydrate metabolism under high night temperatures since reductions were observed only in leaf starch levels. Contrary to that, pistil antioxidant mechanism appeared less sensitive to the high night temperature stress and despite increases in pistil polyamine content accumulation of glucose, sucrose and starch concentrations was observed indicating a perturbation in carbohydrate metabolism.