DIFFERENCES IN THE METABOLIC RESPONSES OF ROOT-TIPS OF WHEAT AND RYE TO ALUMINUM STRESS

The effects of aluminium (Al) ions on the metabolism of root apical me ristems were examined in 4-day-old seedlings of two cereals which diff ered in their tolerance to Al: wheat cv. Grana (Al-sensitive) and rye cv. Dahkowskie Nowe (Al tolerant). During a 24 h incubation period in nutrient solutions containing 0.15 mM and 1.0 mM of Al for wheat and r ye, respectively, the activity of first two enzymes in the pentose pho sphate pathway (G-6-PDH and 6-PGDH) decreased in the sensitive cultiva r. In the;tolerant cultivar activities of these enzymes increased init ially, then decreased slightly, and were at control levels after 24 h. In the Al-sensitive wheat cultivar a 50% reduction in the activity of 6-phosphogluconate dehydrogenase was observed in the presence of Al. Changes in enzyme activity were accompanied by changes in levels of G- 6-P - the initial substrate in the pentose phosphate pathway. When whe at was exposed for 16 h to a nutrient solution containing aluminium, a 90% reduction in G-6-P concentration was observed. In the Al-tolerant rye cultivar, an increase and subsequently a slight decrease in G-6-P concentration was detected, and after 16 h of Al-stress the concentra tion of this substrate was still higher than in control plants. This d ramatic Al-induced decrease in G-6-P concentration in the Al- sensitiv e wheat cultivar was associated with a decrease in both the concentrat ion of glucose in the root tips as well as the activity of hexokinase, an enzyme which is responsible for phosphorylation of glucose to G-6- P. However, in the Al-tolerant rye cultivar, the activity of this enzy me remained at the level of control plants during Al-treatment, and th e decrease in the concentration of glucose occurred at a much slower r ate than in wheat. These results suggest that aluminium ions change ce llular metabolism of both wheat and rye root tips. In the Al-sensitive wheat cultivar, irreversible disturbances induced by low doses of Al in the nutrient solution appear very quickly, whereas in the Al-tolera nt rye cultivar, cellular metabolism, even under severe stress conditi ons, is maintained for a long time at a level which allows for root el ongation to continue.