Aluminum resistance in wheat (<i>Triticum aestivum</i>) is associated with rapid, Al‐induced changes in activities of glucose‐6‐phosphate dehydrogenase and 6‐phosphogluconate dehydrogenase in root apices

Abstract

We have investigated the effect of aluminum (Al) on the activity of glucose‐6‐phosphate dehydrogenase (G6PDH; EC 1.1.1.49) and 6‐phosphogluconate dehydrogenase (6PGDH; EC 1.1.1.44) isolated from 5‐mm root apices of 4‐day‐old wheat ( Triticum aestivum ) cultivars differing in resistance to Al. Rapid increases in G6PDH and 6PGDH activities were observed in Al‐resistant cultivars (PT741 and Atlas 66) during the first 10 h of treatment with 100 μ M Al, while no change in the activity of either enzyme was observed in Al‐sensitive cultivars (Katepwa and Neepawa) during a 24‐h exposure to Al. The Al‐induced increases in enzyme activities observed in the Al‐resistant PT741 appear to reflect an induction of protein synthesis since the increases were completely abolished by 1 m M cycloheximide. No differences in G6PDH and 6PGDH activities were observed between the Al‐sensitive and the Al‐resistant genotypes when Al was supplied in vitro. Under these conditions, an increase in Al concentration from 0 to 1.4 m M caused a gradual decrease in activity of both enzymes, irrespective of the Al‐resistance of whole seedlings. Aluminum‐sensitive and aluminum‐resistant cultivars also differed in the rate and extent of accumulation of slowly‐exchanging Al in 5‐mm root apices. During the first 6 h of Al treatment, Al accumulation was only 10% more rapid in Katepwa than in PT741. After 24‐h exposure, accumulation in the Al‐sensitive Katepwa, was two‐fold higher. A decline in Al accumulation in a slowly‐exchanging compartment as well as a decrease in activities of G6PDH and 6PGDH were found in the Al‐resistant PT741, when seedlings were transferred to Al‐free treatment solutions after 16‐h exposure to 100 μ M Al. These results suggest that rapid induction of G6PDH and 6PGDH in the Al‐resistant line PT741 by Al may play a role in the mechanism of Al resistance, possibly by regulation of the pentose phosphate pathway.