Abstract: | It has been established that Kalanchoe blossfeldiana and Xanthiumpensylvanicum require CO2 during the light period of short daysfor successful photoperiodic induction of flowering, even ifall but the induced leaf are held in normal air. In X. pensylvanicumfloral induction in normal air was independent of the starchstatus of the leaves but when reserves were reduced, lack ofCO2 in the light suppressed floral induction to an even greaterextent. Injection into the induced leaf (Kalanchoe) or leaftip feeding (Xanthium) of carbohydrates, organic and amino acidsor several other metabolites failed to substitute for the CO2requirement for induction. A small response was produced by10 mg ml1 sucrose in X. pensylvanicum while in normalair 25 parts 106 ATP reduced the time to flowering inK. blossfeldiana and 104 M proline was inhibitory. Anexperiment on the light requirement established a need for redlight ( max 660 nm) during photoperiods but red light alonedid not facilitate maximal induction. It is concluded that someearly, possibly labile, product of photosynthetic CO2 fixationis essential to floral induction in these species. |