Cytokinin and inhibitor activity in roots and stems of sugar maple seedlings through the dormant season

Cytokinin and inhibitor activity were followed in the roots and stems of 2-year-old maple seedlings exposed to normal overwintering conditions from early November through April. The production of new roots was also monitored, and all measurements were repeated with dormant control seedlings placed in a greenhouse from the beginning of the experiment and provided with warm temperatures and extended photoperiods. The level of cytokinin-like substances increased in the roots and stems of the outside group in March after a large surge in root activity that began in late February and continued through April. Cytokinins peaked just before budbreak, with the highest levels detected in the lateral roots. Three bands of activity were present on the chromatograms at Rfs 0.1, 0.6, and 0.9. Large cytokinin peaks were also observed in the non-chilled seedlings and were associated with two periods of active root growth and abnormal bud flush in the fall and spring. Abscisic-acid-like activity was detected in the roots and stems of both greenhouse and exposed seedlings, but it remained essentially constant in the stems. Changes that occurred in the roots were not associated with emergence of the buds from the dormant condition.