Chiral synthesis of (+)-8′-demethyl abscisic acid

An enantioselective synthesis of (+)-8′-demethyl ABA (2) is described. The chiral intermediate 7 was prepared by yeast reduction of a substituted monoprotected cyclohexa-2,5-dien-1,4-dione (9) synthesized through a phenol oxidation. The scope and limitations of the phenol oxidation is described. 8′-Demethyl ABA shows ABA-like activity in wheat embryo germination inhibition, showing that the 8′-methyl group is not essential for biological activity. Key words: abscisic acid, phenol oxidation, yeast reduction.

Interaction of abscisic acid and jasmonic acid on the inhibition of seed germination and the induction of freezing tolerance

The possible interaction of the two growth regulators, abscisic acid and jasmonic acid, on the inhibition of seed germination and the induction of freezing tolerance in bromegrass (Bromus inermis Leyss) cell cultures was investigated. Both of these processes are known to be affected by exogenous abscisic acid. Alfalfa (Medicago sativa), cornflower (Centurae gynura), cress seed (Lepidium sativum), maize (Zea mays), and wheat (Triticum aestivum) seeds were treated with varying concentrations of abscisic acid and jasmonic acid, either alone or in combination. In all species, seed germination was inhibited by 10 μM abscisic acid at 23 °C. In contrast, at 23 °C, jasmonic acid was partially inhibitory only at 100 μM; however, 10 μM jasmonic acid inhibited germination in all species at 10 °C. Jasmonic acid in combination with abscisic acid resulted in a higher degree of germination inhibition at 23 °C in all species than either growth regulator applied separately. Treatment of a bromegrass suspension cell culture with 75 μM abscisic acid at 25 °C for 7 days increased the freezing tolerance from −10 °C to lower than −35 °C. In contrast, jasmonic acid (0.25–75 μM) had no detectable effect on freezing tolerance. Jasmonic acid in combination with suboptimal concentrations of abscisic acid, however, enhanced the abscisic acid-induced freezing tolerance in these cells. In contrast, a combination of 75 μM abscisic acid and 25 or 75 μM jasmonic acid reduced the freezing tolerance of these cells compared with treatment with abscisic acid alone. Key words: abscisic acid, freezing tolerance, germination, jasmonic acid.

The influence of surfactants on transpiration of strawberry leaves

Surfactants introduced into strawberry (Fragaria grandiflora Duch. cv. Redgauntlet) leaves in doses of 5.5 × 10−4 – 5.5 × 10−2 μmol per leaf blade decreased the transpiration rate of treated leaves regardless of the electrical charge brought to the membranes. A 5.5 × 10−2 μmol dose of surfactants applied during constant illumination caused almost the same decrease in transpiration as a dose of 7.5 × 10−4 μmol of abscisic acid. Surfactants also accelerated the decrease in transpiration in plants grown in the dark, and there was a consistent rate of solute efflux from guard cells. Fusicoccin applied to plants under the influence of surfactants or abscisic acid caused a sustained increase in the transpiration rate. Mannitol and sucrose caused a temporary increase in transpiration rate. KCl increased transpiration when applied after abscisic acid but decreased transpiration when applied after surfactants. These observations suggest that surfactants and abscisic acid influence the guard cell membrane in different ways and that the electrical charge introduced on the plasmalemma surface is not essential in the regulation of stomatal aperture. Key words: abscisic acid, strawberry, surfactants, transpiration.