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.

Cytokinins in Tobacco and Wheat Chloroplasts. Occurrence and Changes Due to Light/Dark Treatment

“…In tobacco leaves the level of all CKs determined was about three times higher at the end of the dark period than at the end of the light period, which shows that the changes observed in C. rubrum (Machácková et al, 1993) are not general and may be correlated with the photoperiodic type of the plant. The relative abundance of individual CKs remained almost unchanged (Tables III and IV).…”

“…We do know from our recent work on the role of CKs in the flowering of Chenopodium rubrum (Machácková et al, 1993) that the levels of free CKs (bases and ribosides) in leaves decrease during the dark period, probably due to changes in the conversion to ribotides. As the first step in unraveling this complex system, we analyzed the CK levels in wheat leaves and in the leaves and chloroplasts of tobacco taken for chloroplast preparation at the end of a 12-h period of light or dark.…”

Dynamics of Cytokinins in Apical Shoot Meristems of a Day-Neutral Tobacco during Floral Transition and Flower Formation1

“…Earlier work in Chenopodium showed that after the photoperiodic induction of flowering, cytokinin content decreased (Machackova et al, 1993). Exogenous cytokinin application after the inductive photoperiod also inhibited flowering in this species (I.…”

Salt Stress Perception and Plant Growth Regulators in the Halophyte Mesembryanthemum crystallinum

“…It appears that the 24-and 26-kD proteins Davelaar, 1981;Taylor et al, 1990). Cytokinins have frequently been implicated as an essential component of the eventual floral response (Bernier et al, 1977;Lejeune et al, 1988;Machackova et al, 1993). Although zeatin and zeatin riboside levels do not increase dramatically in ice plant roots or leaves during the salt-stress period (Thomas et al, 1992b), we do not exclude temporally and spatially localiied changes in growth regulator concentration during salt stress or changes in titer of distinct cytokinins that have been shown to specifically contribute to flowering responses (van der Krieken et al, 1991).…”