BIOCHEMICAL-CHANGES DUE TO WATER-LOSS IN LEAVES OF AMARANTHUS-HYPOCHONDRIACUS L

This paper describes some biochemical changes that occur during the loss of water from detached leaves and from whole plants of Amaranthus hypochondriacus. The petioles of detached leaves were submerged in a PEG solution. After 6 h, their relative water content changed from 90 % to 70 %; during this time there were increases in ammonia, glycinebetaine, glutamate concentration and glutamate synthetase activity. There were no changes in glutamate dehydrogenase activity and proline concentration. The relative water content of leaves from unwatered plants decreased from 90 % to 60 % by the sixth day of drought. During this time there were increases of ammonia, glycinebetaine and proline concentrations and glutamate synthetase activity. There were no changes in glutamate dehydrogenase activity. In spite of the difference in the speed of water loss in the two systems, all biochemical changes occurred at the same relative water content, but not at the same water potential. It is shown that detached leaves are metabolically similar to leaves from whole plants during water loss. It is argued that the changes in relative water content (and perhaps the cell volume) and not the actual water potential determines the biochemical events described here. © 1991, Gustav Fischer Verlag, Stuttgart. All rights reserved.