ULTRASTRUCTURAL INVESTIGATIONS AND EDX-ANALYSES OF AL-TREATED OAT (AVENA-SATIVA) ROOTS

Seedlings of Avena sativa were precultivated hydroponically at pH 4.1 and subsequently treated with solutions containing 0 or 400 mu M Al. E lectron microscopic and X-ray microanalytic (EDXA) investigations were carried out on root tips after 1 to 10 days of treatment. Root growth and mitotic activity decreased rapidly upon application of Al. The me ristematic tissues of Al-treated roots showed enhanced vacuolation. Th e cells, however, remained intact after a longer period of Al-treatmen t and no alterations in ultrastructure (for example of the nucleus) we re visible. The EDX analyses of bulk frozen hydrated tissues showed th at Al was predominantly localised in the walls of the outermost cortex cells. One day after onset of Al-stress no intracellular Al was detec table. Even after 10 days with continuous Al-stress, only small amount s of the absorbed Al were localised within the cells. These results su ggest that the plasma membrane is a very effective barrier for Al in o ats. It is improbable that impairments of cytoplasmatic functions are primary effects of Al-intoxication.