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 a nd jasmonic acid, on the inhibition of seed germination and the induct ion of freezing tolerance in bromegrass (Bromus inermis Leyss) cell cu ltures was investigated. Both of these processes are known to be affec ted by exogenous abscisic acid. Alfalfa (Medicago sativa), cornflower (Centurae gynura), cress seed (Lepidium sativum), maize (Zea mays), an d wheat (Triticum aestivum) seeds were treated with varying concentrat ions of abscisic acid and jasmonic acid, either alone or in combinatio n. In all species, seed germination was inhibited by 10 mu M abscisic acid at 23 degrees C. In contrast, at 23 degrees C, jasmonic acid was partially inhibitory only at 100 mu M; however, 10 mu M jasmonic acid inhibited germination in all species at 10 degrees C. Jasmonic acid in combination with abscisic acid resulted in a higher degree of germina tion inhibition at 23 degrees C in all species than either growth regu lator applied separately. Treatment of a bromegrass suspension cell cu lture with 75 mu M abscisic acid at 25 degrees C for 7 days increased the freezing tolerance from -10 degrees C to lower than -35 degrees C. In contrast, jasmonic acid (0.25-75 mu M) had no detectable effect on freezing tolerance. Jasmonic acid in combination with suboptimal conc entrations of abscisic acid, however, enhanced the abscisic acid-induc ed freezing tolerance in these cells. In contrast, a combination of 75 mu M abscisic acid and 25 or 75 mu M jasmonic acid reduced the freezi ng tolerance of these cells compared with treatment with abscisic acid alone.