THE MECHANISM OF ALUMINIUM TOXICITY AND RESISTANCE ON SOME BIOCHEMICAL AND HORMONAL CONTENTS OF HORDEUM VULGARE SEEDLINGS

To investigate the threshold of aluminium toxicity and tolerance in Hordeum vulgare plants, the grains were presoaked in Al-2(SO4)(3) (0, 10, 2, 0.4 and 0.081 mu M) for 6 h, sown in plastic pots, and samples were taken when plants were 10 and 30 days old. Aluminium, either steeply (0.08 mu M)or slightly (0.4 mu M), raised all measured growth criteria (mean length of shoots and roots, mean number of leaves and lateral roots, and mean fresh and dry weights of plants), the contents of each of total chlorophyll, total pigments, photosynthetic rates, reducing sugars, starch, total sugars, the levels of each of potassium, magnesium, phosphorus, calcium and growth promoters (auxins, gibberellins, cytokinins), and the activity of invertase, whereas higher concentrations (2 and 10 mu M) obviously reduced them. Reversibly, Al at lower concentrations decreased the carotenoid and ABA contents and the activity of IAA-oxidase while higher concentrations elevated them. Al, at all rates, positively accumulated ascorbate, sodium and iron contents, and raised the activities of alpha- and beta-amylases.