732 (PS 7) EFFECT OF LIGHT ON ENDOGENOUS IAA AND IBA CONCENTRATIONS DURING THE INDUCTIVE PHASE OF ROOTING IN MALUS PUMILA M.9 JORK

Abstract

Shoots of M.9 Jork, grown in vitro, were treated with IBA and then incubated in the dark or light for 5 days to determine the effect of light on endogenous IAA and IBA concentrations during root initiation. Incubation in the dark resulted in significantly greater percentages of rooting and more roots per plant than when the shoots were placed in the light during the inductive period. Uptake of IBA continued throughout the 5 days with both IAA and IBA concentrations in the basal portion of the stems increasing during this period. The increase of both free and total IBA was significantly greater than that of IAA. Relatively little IBA was converted to IAA. An increase of peroxidase activity was noted in the dark, resulting in less free IAA being present in the dark than in the light. Considering the greater amount of IBA relative to that of IAA, however, we concluded that IBA itself, and not its conversion to IAA, is the active agent during root initiation.