Effect of Water-Deficit Stress During Reproductive Development On Polyamine Content of Cotton Flowers

Polyamines, putrescine (PUT), spermidine (SPD) and spermine (SPM) are ubiquitous components of all living cells. Apart from their participation in numerous physiological and metabolical functions of the plant, they are also implicated in plants’ responses under conditions of abiotic stress. Previous research in other crops has indicated that polyamines and changes in their concentrations are associated with drought tolerance under conditions of water deficit stress, however no information exist on cotton (Gossypium hirsutum L.). A field study was conducted in 2011 in two locations (Fayetteville, AR, and Lubbock, TX) in order to investigate the effect of water stress during flowering on polyamine metabolism of the cotton flower and its subtending leaf. Cotton cultivar ST5288B2F was planted in both locations and treatments consisted of control (well watered) and water-stress (irrigation was withheld for two weeks at the onset of flowering). First position white flowers and their subtending leaves were collected at the end of each week and used to determine polyamine concentrations. Putrescine and spermidine levels of water-stressed pistils and leaves were significantly higher compared to the control. Pistil and leaf spermine content significantly increased under drought conditions in one location, remaining unaltered in the other one. Growth chamber experiments were also conducted in 2011-2012, with two cotton cultivars differing in drought tolerance, ST5288B2F (average drought-tolerant) and Siokra L23 (drought-tolerant). According to our results cotton ovaries contained significantly higher levels of total polyamines compared to their subtending leaves under both control and water stress conditions. Water-deficit stress significantly increased PUT concentrations in ST5288B2F, while SPM levels significantly decreased in Siokra L23. The results indicated that water-deficit stress significantly affected cotton polyamine metabolism in reproductive structures and their subtending leaves, however no clear relationship between drought-tolerance and changes in polyamine accumulation was established.