Histochemical localization of enzyme activity during floral evocation in the shoot apical meristem ofSinapis alba

Summary Vegetative plants ofSinapis alba, a long-day species, were induced to flower by exposure to a single 20-hours day. Acid phosphatase, ribonuclease and succinic dehydrogenase activities were investigated by histochemical procedures at different times during floral evocation of the shoot apical meristem. There was an increase in reaction intensity for the three enzymes. Stimulation of acid phosphatase activity began at the 14th hours after the beginning of the long day; ribonuclease at the 18th hours, and succinic dehydrogenase at the 22nd hours. For the first two enzymes, activities returned to control values by 54 hours whereas succinic dehydrogenase activity was still increasing at 54 hours. Results are discussed in relation to other events which are known to occur in the meristem ofSinapis during the transition from the vegative to the reproductive condition.