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Two photoperiodic cotton (Gossypium hirsutum L.) strains (T185 and T466) which had been empirically selected because of poor performance and two strains (T25 and T256) selected because of enhanced performance under field water stress were evaluated for stress-induced changes in their organic acids and carbohydrates. Profiles and quantitation of organic acids and carbohydrates from aqueous extractions of cotton leaf tissue were determined by high performance liquid chromatography. In all cases, the water-stressed plants showed two to five times greater amounts of organic acids and carbohydrates over the values determined for the irrigated samples. Under stress, sucrose accumulation was observed in wilting strains (poor performers) probably related to rate of translocation out of the leaf. The most dramatic response to water stress was the accumulation of citric acid in strains T25 and T256 as compared to T185 and T466. Citric/malic acid ratios for both the irrigated and waterstressed samples of T25 and T256 were twice those of T185 and T466.Organic acids and carbohydrates have been implicated in various roles in the metabolic and physiological responses of plants to water stress. Early papers by reported that, at low water levels, carbohydrates accumulated in cotton plants which had complete fruit loads. In cotton leaves, drought caused large reductions in starch concentrations, variable effects on sucrose, and an increase in hexose sugar. The gains in sugars were substantial on a relative basis but were minor in actual amounts. They concluded that drought appears to depress carbohydrate utilization by the cotton plant to a greater extent than it does photosynthesis (7).Malic, citric, and oxalic acids are frequently found in large amounts (several percent of the dry weight of the tissue) in mature tissues or organs of plants (4). For cotton, higher concentrations of organic acids are found in the leaves than in other vegetative parts, frequently at 10% of the basis of dry weight (8). The major acids accounting for a total content of approximately 10% of the dry weight of cotton leaves were identified as citric, malic, and oxalic, with malic usually present in the greatest amount. It was reported that drought caused large reductions in concentrations of citric acid with gains in malic acid but with overall maintenance of the level oftotal organic acids (8

To reduce damage by drift-levels of the herbicide 2,4-dichlorophenoxyacetic acid, we have engineered the 2,4-D resistance trait into cotton (Gossypium hirsutum L.). The 2,4-D monooxygenase gene tfdA from Alcaligenes eutrophus plasmid pJP5 was isolated, modified and expressed in transgenic tobacco and cotton plants. Analyses of the transgenic progeny showed stable transmission of the chimeric tfdA gene and production of active 2,4-D monooxygenase. Cotton plants obtained were tolerant to 3 times the field level of 2,4-D used for wheat, corn, sorghum and pasture crops.

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