Osmotic Adjustment and Accumulation of Proline in Cotton Genotypes Under Water-Deficit Stress

Cotton has several mechanisms to alleviate the effects of drought stress; however, the physiological and metabolic functions vary among all available genotypes. Osmotic adjustment through accumulation of compatible solutes is one of the major mechanisms plants use to acclimate to water-deficit conditions but information on osmotic adjustment in reproductive units of cotton plants has not been clarified. The objective of this study was to characterize the osmotic adjustment in leaves and reproductive units of a range of cotton genotypes grown under water-deficit stress. A growth room experiment was conducted at the University of Arkansas in Fayetteville, AR. Treatments consisted of four cotton (Gossypium hirsutum L.) genotypes, DP0912, PHY499, Siokra L23, and ST5288, and two water regimes, an untreated control with no water-deficit stress, and water deficit. Water-stress was imposed at flowering by withholding water from the water-stressed plants group until the plant’s stomatal conductance (gs) reach approximately 20 mmol m^-2s^-1. Osmotic potential was measured and samples were collected for proline content from the upper first position white flowers and their subtending leaves. Variability in osmotic adjustment exists among the cotton genotypes and between the plant organs under water-deficit stress. PHY499 had higher osmotic adjustment in the leaves of water-stressed plants through more negative osmotic potential and higher proline accumulation. ST5288 appeared to have higher osmotic adjustment in both leaves and ovaries of water-stressed plants due to the higher proline accumulation in the leaves and ovaries and more negative osmotic potential in the ovaries. DP0912 and Siokra L23 accumulated higher amount of proline in the leaves and ovaries, but it did not increase the osmotic potential of the plant organs in both genotypes.