Osmotic Adjustment in Commercial Cotton Cultivars Under Drought Stress

Water is one of the most important factors for crop growth and productivity. Cotton is considered to be a relatively drought tolerant crop but plant metabolism and yield are still compromised under drought conditions. Differences in drought tolerance exist between cultivars but the metabolic reasons for this that could be used to find traits for enhancing drought tolerance have not been clearly elucidated. Under drought stress, osmotic adjustment occurs in plant cells through accumulation of compatible solutes in the cytosol and plays a role of reducing the osmotic potential of the cell in order to maintain cell turgor and growth. The objective of this study was to evaluate the osmotic adjustment of two commercial cotton cultivars under drought stress. A field experiment was conducted in Lubbock, TX in 2013. Treatments were consisted of two cotton (Gossypium hirsutum L.) cultivars, ST5288 and PHY499, and two water regimes, well-watered and water-stressed. Water was withheld for 10 days at flowering and the field was re-watered 12 hours before the measurements. Osmotic potential were measured and samples were collected for proline content. Osmotic adjustment was greater in leaves and ovaries under water stress in both cultivars compared with well-watered conditions. But the difference in osmotic potential was significantly higher in leaves of the ST5288 and the ovaries of the PHY499. Water stress enhanced proline concentrations in both organs of the two cultivars. However, the proline accumulation due to the water stress was considerably higher in the ovaries than in the leaves in both cultivars. As in most plants, leaf osmotic potential is reduced under drought conditions, but cotton seems to have the ability to osmotically adjust and maintain a higher leaf turgor potential.