APPEARANCE OF PEROXIDASE ISOZYMES IN FLORAL-INITIATED SHOOT APICES OF PHARBITIS-NIL

A novel biochemical assay system for detecting the early stage of flowering is reported. Peroxidase isozymes in shoot apices of Pharbitis nil plants that had been exposed to flower-inducing or non-inducing conditions were analyzed by isoelectric focusing in polyacrylamide gels and activity staining for peroxidase. Several isozymes with pH 8.5-8.8 appeared for the first time 7 days after the beginning of short-day treatment, but not after nightbreak (non-inducing) treatment. When shoot tips were cultured in vitro, these same isozymes also appeared after short-day treatment but not after night-break treatment. The extent of the appearance of these isozymes was reduced by exposure to high or low temperature during the inductive dark period and removal of cotyledons after the inductive dark period. Such treatments also reduced the extent of flowering. The appearance of an isozyme with pH 8.5 was more closely correlated with flowering than that of the other isozymes. From these results, the appearance of this peroxidase isozyme in shoot apices is discussed as a biochemical marker of flowering in intact plants and in cultured shoot tips.