CHANGES IN THE ULTRASTRUCTURE OF THE ROOT-TIP OF WHEAT FOLLOWING EXPOSURE TO ALUMINUM

Investigations have been carried out on morphological changes induced by aluminium ions in roots of wheat seedlings (Triticum aestivum L. cv . Vulcan). Lesions were evident on the surface of the roots after 4-8 h of exposure, and within 24 h there was increased vacuolation, loss o f turgor, and severe cytoplasmic disorganisation in epidermal and peri pheral cap cells. The central cap and cortical layers were also severe ly damaged by aluminium, but changes in the meristematic cells became evident only after more prolonged exposure of roots to aluminium. Mobi lisation of starch in amyloplasts of peripheral and central cap cells of aluminium-stressed roots was particularly noticeable, and this was accompanied by an increase in the amount of extractable activity of st arch-degrading enzymes. The possibility that the mobilisation of starc h is linked to a coincident increase in fermentative metabolism in Al- stressed wheat roots is considered.