Studies on the Role of Photosynthesis in the Photoperiodic Induction of Flowering in the Short-Day Plants Kalanchoe blossfeldiana Poellniz and Xanthium pensylvanicum Wallr: II. THE EFFECT OF CHEMICAL INHIBITORS OF PHOTOSYNTHESIS

The role of photosynthesis in flower induction in the short-dayplants Kalanchoe blossfeldiana and Xanthium pensylvanicum wasinvestigated by chemical suppression of photosynthesis and preventionof chlorophyll formation in the induced leaf. ‘Bleaching’leaves with streptomycin completely prevented flowering in X.pensylvanicum at concentrations shown to reduce the chlorophylland carotenoid content of the leaf significantly. Such leaveswere unable to induce flowering even when supplied with sugarsand other photosynthetic products. Photosystem II inhibitors,DCMU and cadmium ion, inhibited induction in both species aswell as suppressing photosynthesis (as tested by O₂ evolutionand starch production) whereas the photosystem I inhibitor,metronidazole, had no effect. Antimycin A inhibited floweringin K. blossfeldiana and may have a similar site of action toDCMU. Neither ammonium ion nor DBMIB, which acts upon plastoquinone(i.e. between PS I and PS II in the ‘Z scheme’),had any effect on floral induction and it is argued that theinductive process is independent of photosynthetic phosphorylationbut a step in the electron transport pathway between the sitesof action of DCMU and DBMIB may be crucial. DSPD and its hydrolysisproduct, salicylaldehyde, suppressed flowering in K. blossfeldianabut the uncertainty regarding their chemistry precludes anyfirm conclusions regarding the nature of their action.