Levels of short-chain fatty acids and of abscisic acid in water-stressed and non-stressed leaves and their effects on stomata in epidermal strips and excised leaves.

Straight-chain saturated fatty acids (C6-C11) and abscisic acid (ABA) accumulate in the leaves of Phaseolus vulgaris L. and Hordeum vulgare L. under water stress. ABA and certain of the fatty acids, particularly decanoic and undecanoic acid, can inhibit stomatal opening and cause stomatal closure in epidermal strips of Commelina communis L. depending on the incubating medium used. 10(-4) M (±)-ABA inhibits opening in media containing either high or relatively low concentrations of KCl but causes closure only in the latter medium. The fatty acids (at 10(-4) M) prevent opening in both media while significant closure of open stomata was caused only by undecanoic acid in both media and, additionally, by decanoic acid in the low-KCl medium. 10(-4) M formic acid also caused stomatal closure and prevented opening to significant extents in the low-KCl medium (it was not tested in the high-KCl medium). The efficacy of undecanoic acid in causing 50% inhibition of opening is about three orders of magnitude lower than that of ABA. At a concentration of 10(-3) M, nonanoic, decanoic and particularly undecanoic acid and all-trans-farnesol cause increased cell leakage in Beta vulgaris L. root tissue. Undecanoic acid (10(-4) M) also causes some loss of guard cell integrity in C. communis within 1.5 h of treatment. ABA (10(-4) M) reduces transpiration rates in barley and C. communis leaves when applied via the transpiration stream but decanoic and undecanoic acids did not have this effect. Transpiration was not affected when ABA or the fatty acids were applied to the leaf surfaces.