EFFECTS OF DORMANCY-BREAKING CHEMICALS ON ABA LEVELS IN BARLEY-GRAIN EMBRYOS

The endogenous ABA contents of dormant and nondormant barley grains we re determined following application of different compounds to break do rmancy. The chemicals used for breaking of dormancy in intact dormant grains were weak and strong acids, alcohols, hydrogen peroxide, cyanid e, nitrate, salicylic acid, gibberellic acid and fusicoccin. The dorma ncy-breaking compounds could be classified into two major groups: comp ounds that caused a decrease in endogenous ABA (crass I) and compounds which did not affect endogenous ABA (class II). Class I compounds inc luded gibberellic acid, ethanol, hydrogen peroxide, nitrate, salicylic acid; class II compounds were fusicoccin, acid (H2SO4), sodium azide, n-caproic acid. In addition, these dormancy-breaking compounds were a ble to stimulate the germination rate when applied to embryos isolated from dormant grains. The concentrations necessary for stimulation of germination of isolated embryos were much lower than the concentration s for breaking the dormancy of intact grains. After embryos were isola ted from dormant grains and incubated in water, ABA was determined in both embryos and in the incubation media. The class I compounds stated above also reduced ABA content in the incubation medium of isolated e mbryos, while class II compounds had no effect on ABA content of the m edium. External application of ABA could overcome the effect of dorman cy-breaking compounds of class I but not of class II. The results sugg est that in the presence of the agents belonging to class II, ABA resp onsiveness of isolated embryos from dormant grains is decreased, compa red to nontreated embryos.