MEMBRANE THERMOSTABILITY AND NITRATE REDUCTASE ACTIVITY IN RELATION TO WATER STRESS TOLERANCE OF YOUNG SUGAR-CANE PLANTS.

An assessment of tolerance to water stress based upon measurements of cellular membrane thermostability and in vivo nitrate reductase activity (NRA) was made using young leaves of sugar-cane (Saccharum officinarum L. commercial hybrids, Co 419, Co 740 and Co 1148) subjected to stress (51 to 61 d old) and subsequent hydration. An average reduction in leaf water potential (Ψ ) from -0.97 to -1.91 MPa was associated with a decrease in NRA from 2.68 to 1.13 Ψmol g f. wt h , and an increase of the membrane injury from 30.8 to 70.9%. A highly significant positive correlation between Ψ and NRA and a negative correlation between Ψ and membrane injury were demonstrated. As Ψ declined, the concentration of malondialdehyde, a lipid peroxidation product, doubled. Following rehydration, at 63 d, increases in Ψ and NRA were higher than those of membrane thermostability and malondialdehyde concentration.