Effect of 2,4-Dichlorophenoxyacetic Acid on Growth and on β-Glucan Synthetases of Peroxyacetyl Nitrate Pretreated Avena Coleoptile Sections

Coleoptile sections from Avena sativa L. were exposed to non-lethal concentrations of peroxyacetyl nitrate (PAN). The sections were then incubated in solutions of 50 mM glucose plus 2.5 mM potassium phosphate with various concentrations of 2,4-dichlorophenoxyacetic acid (2,4-D). Growth after 4 hours was measured. A corresponding series of experiments was carried out and the effect of the 2,4-D treatments on enzymes utilizing uridine diphosphate glucose (¹⁴C-glucose) to form glucolipid and β-glucans including cellulose was determined. Growth in the PAN-treated sections was inhibited less at optimal and superoptimal auxin levels than at low auxin levels. Glucolipid synthetase activity was only slightly inhibited by PAN pretreatment and was reduced by increasing levels of auxin. Responses of alkali-soluble glucan and cellulose synthetases were similar to growth in both control and PAN treated tissues. It was concluded that the earlier reported response of cell wall metabolism in vivo probably is due to effects on these enzyme levels.