Plants of sugarcane, cv. Co 1148, were subjected to salinisation with 200 milliequivalents L-1 of Cl- -type salts mixture (having Na+, Ca2+ and Mg2+ as 3 :1:1 and Cl- and SO42- as 4:1 on a milli- equivalent basis) for two weeks or more during the tillering phase. Soluble sugar concentrations increased by 55% in the blades of recently matured leaves (source tissues) and by nearly 225% in the elongating sheath bases (sink tissues) as a result of salinisation. Leaf elongation within 3 h of desalin- isation was much faster than for the non-saline controls. The accumulated sugars also dropped in the rapidly elongating sheath bases by 43% during this period after desalinisation. Further, the drop in sugar levels upon desalinisation was of greater magnitude in the more rapidly growing sheath bases. The present studies indicate that even though the supply of carbohydrates from the source tissues is reduced, the sink tissues are not able to make use of these sugars under saline conditions. As Na+ and Cl- concentrations did not change within 3 h of desalinisation, the ions themselves did not appear to affect metabolic activities of the sink tissues; this suggestion is further supported by the utilisation of accumulated sugars within 3 h of desalinisation.
SUMMARYAn 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 (y,) from -0-97 to -1 91 MPa was associated with a decrease in NRA from 268 to 113 /imol g f. wt^* h~\ and an increase of the membrane injury from 30-8 to 70-9%. A highly significant positive correlation between y^ ^^^ NRA and a negative correlation between \\f^^ and membrane injury were demonstrated. As y^ declined, the concentration of malondialdehyde, a lipid peroxidation product, doubled. Following rehydration, at 63 d, increases in y^ and NRA were higher than those of membrane thermostability and malondialdehyde concentration.
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