Cytokinins in photoperiodic induction of flowering in Chenopodium species

Abstract

Changes in cytokinin (zeatin – Z, zeatin riboside – ZR, isopentenyladenine – iP, isopentenyladenosine – iPA) levels were determined under light regimes inductive and non‐inductive for flowering in leaves, stems, roots and apical parts of short‐day Chenopodium rubrum and long‐day Chenopodium murale. In leaves. stems and roots of both plant species the level of cytokinins (in C. rubrum of Z and ZR, in C. murale of Z. ZR, iP and iPA) decreased by about 50% during the dark period and increased again during the subsequent light period, No significant changes in cytokinin levels were observed in continuous light. In apical parts of C. rubrum cytokinin level (Z, ZR, iP) was dramatically increased (by 400–500%) at the end of the dark period and decreased to about the original value during the following light period, while no changes were observed in continuous light. In apical parts of C. murale the level of cytokinins doubled during floral induction consisting of 10 days of continuous light. A red (R) break (15 min at the 6th h of darkness), which prevents flowering in C. rubrum, has no significant effect on cytokinin levels in leaves at the end of darkness. Cytokinin levels increased 1 h after R and decreased again rapidly. On the other hand, the increase of cytokinin level in the apical parts of C. rubrum was largely prevented by the R break. These effects of R on cytokinin levels were not reverted by far‐red (FR), while the effect on flowering was reverted. It may be concluded that there is no correlation between changes in cytokinin levels in leaves. Stems and roots and photoperiodic flower induction, as both species, representing different photoperiodic types, showed similar changes under the same light regime. The increase of cytokinin levels in apical parts of both photoperiodic species during floral induction suggests a role (increased cell division and branching) for cytokinins in apex evocation.