THE EFFECT OF ALUMINUM ON RESPIRATION OF WHEAT ROOTS

The effects of aluminium ions on respiration of excised root apices fr om wheat (Triticum aestivum L. cv. Vulcan) and on isolated mitochondri a have been investigated. Addition of 75 muM aluminium to the growth m edium of 4-day-old seedlings inhibited O2 uptake by excised root apice s by 23 and 35% after 12 and 24 h, respectively. This decreased rate o f respiration was initially caused by inhibition of the cytochrome pat hway of mitochondrial electron transport. The cyanide-insensitive, alt ernative pathway was inhibited only after more prolonged exposure to a luminium. Mitochondria isolated from roots of aluminium-treated seedli ngs had reduced oxidative capacity with substrates that supply electro ns to Complexes I and II, compared with mitochondria from roots of unt reated control seedlings. The state 3 and state 4 rates of O2 uptake a nd the uncoupled rates with these substrates were also inhibited when aluminium was added directly to reaction mixtures containing mitochond ria isolated from untreated plants. In contrast, when aluminium was ad ded to reaction mixtures oxidizing exogenous NADH, state 4 O2 uptake w as stimulated, whereas no effect was observed on the state 3 rate or t he rate in the presence of uncoupler. The results suggest that alumini um initially affects electron flow through Complexes I and II, and tha t after more prolonged exposure, aluminium may also interact with othe r sites in mitochondria.