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-day plants Kalanchoe blossfeldiana and Xanthium pensylvanicum was investigated by chemical suppression of photosynthesis and prevention of chlorophyll formation in the induced leaf. 'Bleaching' leaves with streptomycin completely prevented flowering in X. pensylvanicum at concentrations shown to reduce the chlorophyll and carotenoid content of the leaf significantly. Such leaves were unable to induce flowering even when supplied with sugars and other photosynthetic products. Photosystem II inhibitors, DCMU and cadmium ion, inhibited induction in both species as well as suppressing photosynthesis (as tested by 02 evolution and starch production) whereas the photosystem I inhibitor, metronidazole, had no effect. Antimycin A inhibited flowering in K. blossfeldiana and may have a similar site of action to DCMU. 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 the inductive process is independent of photosynthetic phosphorylation but a step in the electron transport pathway between the sites of action of DCMU and DBMIB may be crucial. DSPD and its hydrolysis product, salicylaldehyde, suppressed flowering in K. blossfeldiana but the uncertainty regarding their chemistry precludes any firm conclusions regarding the nature of their action.