Water Relations of Cotton Plants under Nitrogen Deficiency: I. Dependence upon Leaf Structure

Cotton plants (Gossypium hirsutum L.) grown on deficient levels of N exhibited many of the characteristics associated with drought resistance. In N-deficient plants, leaf areas and leaf epidermal cells were smaller than at the same nodes in high-N plants. N-deficient leaves lost only about half as much water per unit change in water potential as did high-N leaves. In addition, they maintained a greater relative water content than high-N leaves at any given potential. Osmotic potentials (determined from pressure-volume curves) were slightly lower in N-deficient leaves. This difference in solute concentration was not from organic acids, which were almost unchanged. Sugar concentrations could account for only about 25% of the difference.Leaves of N-deficient plants contained considerably more dry matter per unit moisture. Most of this difference in dry weight was in the crude cell wall fraction. The pressure-volume curves and other indirect evidence strongly suggested that cell walls of N-deficient leaves were substantially more rigid than cell walls of high-N leaves. The effects of N deficiency on cell wall properties mimic the changes which occur during drought adaptation.