Effect of Water-Deficit Stress On Reproductive Development in the Cotton Pistil.

Water deficit is the major abiotic factor limiting plant growth and crop productivity around the world. Even though cotton is considered to be relatively tolerant to drought, plant growth and yield reduction still occur when water supply is limited or interrupted. However, little is known about metabolic responses to water deficit in the flower. Research is needed to elucidate the metabolic responses of cotton reproductive units under conditions of water stress in order to facilitate methods of amelioration. The objectives of this study were to document and quantify the physiological and biochemical changes that take place in cotton flowers and their subtending leaves when subjected to limited water supply. It was hypothesized that water-deficit stress would severely impair gas exchange functions which consequently would result in perturbation of carbohydrates and energy production metabolism of cotton reproductive units.

Growth chamber experiments were conducted in 2009-2010 at Altheimer Laboratory in Fayetteville, University of Arkansas. Cotton (Gossypium hirsutum L.) cultivar ST5288B2F was planted into 2L pots with Sun-Gro horticulture mix and growth chambers were set for normal conditions of 30/20°C (day/night), ±60% relative humidity, and 12h photoperiods.  Plants were arranged in a completely randomized block design with 20 replications and half-strength Hoagland’s nutrient solution was applied daily in order to maintain adequate nutrients and water. The water-deficit treatments consisted of: (1) Untreated control, (2) Water-deficit stress during squaring and, (3) Water-deficit stress during flowering. Measurements of stomatal conductance, fluorescence, and respiration were taken from the fourth main-stem leaf and flowers for carbohydrate and antioxidant content were sampled whenever they were available. The results showed that both early (during squaring) and late (during flowering) water-deficit stresses had a detrimental impact on carbohydrate metabolism of cotton flower pistils. Late-stress caused glucose, fructose and sucrose levels to significantly decrease, which resulted in a reduction in respiration rates. The early stress caused a similar reduction to glucose levels which was not accompanied by a corresponding reduction in respiration rates. Additionally fructose and sucrose levels of early-stressed flowers were significantly higher than those of the late-stressed flowers indicating a perturbation in the breakdown and interconversion of carbohydrates in the flower. These responses would most likely result in a compromise of fertilization efficiency and seed set.