The effects of water stress on abscisic-acid levels and metabolism in roots of Phaseolus vulgaris L. and other plants.

Abscisic-acid (ABA) levels in roots of bean plants exposed to a-4 bar stress in the root medium increased ca. 10fold within 1 h and 16fold by the end of the 2nd h. Several types of experiments indicated that there is no transport requirement from the shoot for the increase to occur. ABA levels in roots from pea (Pisum sativum L.) and sunflower (Helianthus annuus L.) also increased in response to a-4 bar stress, although not as dramatically as in bean. When (S)-[2-(14)C]-ABA was fed to excised bean roots dihydrophaseic acid (DPA) was the major metabolite formed. The levels of endogenous DPA and phaseic acid increased markedly during a 27-h stress period. These results are consistent with a possible role for ABA in roots of water-stressed plants.