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, indole-3-acetic acid, and cytokinins on dormancy of quackgrass (Elytrigia repens (L.) Nevski) rhizome axillary buds using exogenous hormone treatments and analysis of endogenous hormones. Exogenous hormone treatments were applied in solution or in lanolin paste to 5-node segments of rhizome with an apical tip intact or removed. Abscisic acid inhibited bud growth except at concentrations of 0.5 – 1 μg ∙ mL−1 when it stimulated 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 acid at concentrations of 0.5 – 5 μg ∙ mL−1 and cytokinins at higher concentrations (i.e., 10 – 100 μg ∙ mL−1). Indole-3-acetic acid also increased elongation of the buds, whereas abscisic acid and cytokinins did not. Levels of endogenous hormones were measured in bud samples: indole-3-acetic acid was quantified as its methyl ester by combined gas chromatography – mass spectrometry – selected ion monitoring; abscisic acid was quantified as its methyl ester by gas chromatography – electron capture; and cytokinins were quantified using a soybean callus bioassay. Hormone levels were generally higher in the most active buds of a 5-node section. Abscisic acid was also measured in buds 24 h after sheath leaf removal, a practice known to promote bud sprouting. Sheath leaf removal had no significant effect on abscisic acid levels. Key words: quackgrass, Elytrigia repens, auxins, abscisic acid, cytokinins, apical dominance.