Water-Deficit Stress On Cotton During Reproductive Development.

Water deficit is a major abiotic factor limiting plant growth and crop productivity around the world. Cotton (Gossypium hirsutum L.) is considered to be relatively tolerant to drought and the effects of water stress on leaf physiology and metabolism have been extensively documented. However, no research exists to our knowledge on the alterations in the physiology and biochemistry of the cotton flower under conditions of water-deficit stress. It was hypothesized that water-deficit stress would impair gas exchange functions which consequently would result in perturbation of carbohydrates of cotton reproductive units. To investigate this hypothesis growth room studies as well as field studies were conducted and the objectives were to document the physiological and biochemical changes that take place in cotton flowers and their subtending leaves when subjected to limited water supply.  Our results indicated that water-deficit stress during flowering significantly compromised leaf gas exchange functions resulting in decreased stomatal conductance and photosynthesis. However, cotton reproductive units appeared to be less drought-sensitive compared to the leaves possibly due to higher glutathione reductase activity. Additionally, limited supply of water significantly affected carbohydrate metabolism of both leaf and pistil resulting in carbohydrate accumulation. Finally, water-deficit stress during flowering had a significant effect on polyamine metabolism of both leaf and pistil, consequently resulting in increases in putrescine, spermidine and spermine in drought-sensitive cultivars. The differential response of polyamine metabolism between drought-sensitive and tolerant cultivars suggests that polyamines could be effective tools not only in selection of drought-tolerant cultivars but also in drought tolerance engineering,  however further research is needed in order to elucidate the exact pathways of their action.