Photosynthetic Efficiency and Antioxidant Activity of Cotton under Drought Stress during Early Floral Bud Development

Abstract

Aims: Identify changes in photosynthetic efficiency, pigment concentration, and enzyme activity in cotton caused by water-deficit stresses during early floral bud development; compare physiological stress responses among cotton cultivars. Study Design: A strip plot design with two water regimes at Lubbock, and a strip split plot design with two water regimes and three cultivars at Marianna, with five replications. Place and Duration of Study: Fields at Quaker Avenue Research Farm of Texas Tech University in Lubbock, TX in 2012 and at the Lon Mann Cotton Research Station of University of Arkansas in Marianna, AR in 2013. Methodology: Water was withheld for 14 days from the water-deficit stress treatment at the appearance of floral buds on the cotton plants. Stomatal conductance and chlorophyll a fluorescence were measured In situ seven and fourteen days after the onset of stress; tissue samples were also collected and analyzed for enzyme activity and pigment concentration. Results: Lower stomatal conductance was observed in plants under water-deficit stress in all instances. Actual quantum yield of photosystem II (ФPSII) varied among the cultivars, with DP 0912 having the highest ФPSII, followed by ST 5288 and PHY 499. The ФPSII and electron transport rate also decreased over time. Pigment concentrations, including Chlorophyll a and b, were reduced by water-deficit stress over time among all cultivars and sampling dates, with the lowest pigment concentrations occurring in DP 0912. Enzyme activity was significantly increased by water-deficit stress, with stressed plants having a 4-fold increase in superoxide dismutase activity, a 10-fold increase in catalase activity, and a 57% increase in ascorbate peroxidase concentration compared with the control. Conclusion: Stomatal conductance and pigment concentration were sensitive to water-deficit stress at squaring development; however, chlorophyll a fluorescence was not responsive to the stress. Increased antioxidant activity appeared to be associated with scavenging of free radicals in cotton. ST 5288 and PHY 499 seemed to have improved tolerance to water-deficit conditions compared to DP 0912. However, further research is needed to identify traits related to drought tolerance of these cultivars.