Sixty-five years of searching for the signals that trigger flowering

This review summarizes the long-term research of photoperiodic flower induction in two Chenopodium species, one of which, C. rubrum, is a short-day plant, while the other, C. murale, is a long-day plant. In the course of purification of "florigenic" extracts inducing flowering in C. rubrum plants kept under noninductive photoperiodic conditions, we did not succeed in identifying its active component(s). During the inductive treatment, the phloem transport of cytokinins was enhanced and their content in the shoot apex greatly increased for some time. The review also summarizes the results of the application of direct electric current to the leaves of C. rubrum plants. This treatment interferes with the transport of some active signal(s) from leaves to the apex, resulting in the inhibition of flowering induction. The problem of the rhythmicity of flowering in C. rubrum plants was considered, particularly, the possibility of melatonin (N-acetyl-5-methoxytryptamin) participation in photoperiodic induction. Melatonin accumulation in darkness appears to determine the amplitude of the flowering rhythm but not its phase or period.