Proline Accumulation by Water and Nitrogen Stressed Cotton1

Germinating and developing cotton (Gossypium hirsutum L.) seedlings were examined for proline accumulation under severe water stress and N deficiency to examine the relationship of N to proline accumulation. Seeds of ‘Coker 201’ were dark‐germinated for 3 days with one‐half desiccated during the last 12 hours. In another experiment, plants were light grown under well watered conditions with or without nutrient solution containing NO3‐N. On the 12th day they were subjected to severe water stress. Dry weight, free amino acids, and plant water potentials were determined after stress developed. Three‐day desiccated cotyledons accumulated 28% more proline than the unstressed controls. Axes of these stressed seedlings, however, did not accumulate free proline. The older water stressed cotyledons and leaves accumulated free proline, but only when the seedlings had an exogenous source of N. Thus under severe N deficiency, proline accumulation ability is imparied in cotton leaf tissue. Free histidine, on the other hand, accumulated in N deficient leaves, but not cotyledons. The results indicate that proline accumulation by water stressed tissue is related to the N status of the tissue as well.