APICAL DOMINANCE IN RHIZOMES OF QUACKGRASS, ELYTRIGIA REPENS - THE EFFECT OF AUXIN, CYTOKININS, AND ABSCISIC-ACID

Experiments were designed to determine the impact of abscisic acid, in dole-3-acetic acid, and cytokinins on dormancy of quackgrass (Elytrigi a repens (L.) Nevski) rhizome axillary buds using exogenous hormone tr eatments and analysis of endogenous hormones. Exogenous hormone treatm ents were applied in solution or in lanolin paste to 5-node segments o f rhizome with an apical tip intact or removed. Abscisic acid inhibite d bud growth except at concentrations of 0.5-1 mu g ..mL(-1) when it s timulated growth: this appeared to be based on an inhibition of apical dominance rather than a stimulation of bud growth per se. Both indole -3-acetic acid and cytokinins stimulated bud growth, indole-3-acetic a cid at concentrations of 0.5-5 mu g . mL(-1) and cytokinins at higher concentrations (i.e,, 10-100 mu g mL(-1)). Indole-3-acetic acid also i ncreased elongation of the buds, whereas abscisic acid and cytokinins did not. Levels of endogenous hormones were measured in bud samples: i ndole-3-acetic acid was quantified as its methyl ester by combined gas chromatography - mass spectrometry - selected ion monitoring; abscisi c acid was quantified as its methyl ester by gas chromatography - elec tron capture; and cytokinins were quantified using a soybean callus bi oassay. Hormone levels were generally higher in the most active buds o f a 5-node section. Abscisic acid was also measured in buds 24 h after sheath leaf removal, a practice known to promote bud sprouting. Sheat h leaf removal had no significant effect on abscisic acid levels.