FLURIDONE-AFFECTED AND LIGHT-AFFECTED CHLOROPLAST ULTRASTRUCTURE AND ABA ACCUMULATION IN DROUGHT-STRESSED BARLEY

The effects of fluridone on leaf anatomy, chloroplast ultrastructure a nd accumulation of drought stress-induced abscisic acid (ABA) were stu died in Hordeum vulgare L. plants grown under different light conition s. Drought stress was induced by allowing the leaves to lose 12 % of t heir fresh weight. The appearance of defective chloroplasts with a des troyed thylakoid membrane system was found in fluridone-treated plants grown under photooxidative conditions as well as in the absence of li ght. Plants grown at a PPF of 600 mu mol.m(-2).s(-1) had 15-fold incre ase in ABA level after dehydration of the leaves followed by a 4 h inc ubation. Fluridone treatment fully blocked the accumulation of stress- induced ABA. Plants gown at a PPF of 40 mu mol.m(-2)s(-1) had diminish ed levels of ABA after imposition of dehydration. Dehydration of dark- grown control barley leaves caused ABA levels to increase 40-fold in 4 h, while plants treated with 0.1 mM fluridone accumulated very little ABA in response to dehydration. The presented results are dicussed in terms of the suggestion that structurally intact and functionally act ive chloroplasts are required for drought stress to elicit a rise in A BA. (C) Elsevier, Paris.