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 (ΨL) from −0.97 to −1.91 MPa was associated with a decrease in NRA from 2.68 to 1.13 Ψmol g f. wt−1h−1, and an increase of the membrane injury from 30.8 to 70.9%. A highly significant positive correlation between ΨL and NRA and a negative correlation between ΨL and membrane injury were demonstrated. As ΨL declined, the concentration of malondialdehyde, a lipid peroxidation product, doubled. Following rehydration, at 63 d, increases in ΨL and NRA were higher than those of membrane thermostability and malondialdehyde concentration.