Drought effects on the water relations of cotton fruits, bracts, and leaves during ontogeny

Abstract Cotton (Gossypium hirsutum L.) yields are strongly influenced by water-deficit stress, but the effects of drought on the water relations of cotton fruits have not been documented. Field and greenhouse studies were conducted to investigate the effects of water deficit on the water status of cotton leaves, bracts, and fruits. Water potential (Ψ) of the capsule wall did not react to drought during the period of fruit expansion. Cotton fruits generally had higher water and osmotic potential, and their water status was less sensitive to drought than that of the subtending leaf and bracts. The insensitivity of cotton fruit water potential to drought can be explained by their isolation from the apoplast of the rest of the plant and their high hydraulic capacitance. The lower Ψ of the leaves may have been the result of the much higher transpiration rate of leaves compared with fruits. Transpiration and stomatal conductance of the sympodial leaf decreased during fruit development. Since gradients in water potential are the driving force for water transport through the xylem, it seems unlikely that cotton fruits receive water through the xylem. The results from this study are in agreement with our earlier hypothesis that the phloem plays an important role in water transport to developing cotton fruits.