Fluridone- and light-affected chloroplast ultrastructure and ABA accumulation in drought-stressed barley

The effects of fluridone on leaf anatomy, chloroplast ultrastructure and accumulation of drought stress-induced abscisic acid (ABA) were studied in Hordeum vulgare L. plants grown under different light conitions. Drought stress was induced by allowing the leaves to lose 12 % of their fresh weight. The appearance of defective chloroplasts with a destroyed thylakoid membrane system was found in fluridone-treated plants grown under photooxidative conditions as well as in the absence of light. Plants grown at a PPF of 600 μmol·m−2·s−1 had 15-fold increase in ABA level after dehydration of the leaves followed by a 4 h incubation. Fluridone treatment fully blocked the accumulation of stress-induced ABA. Plants grown at a PPF of 40 μmol·m−2·s−1 had diminished 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 active chloroplasts are required for drought stress to elicit a rise in ABA.