Is the Root Effect on Flowering of Chenopodium rubrum Mediated by Cytokinins?

Abstract.

Root removal enhances flowering in the short day plant Chenopodium rubrum. The extent of this effect depends on the de-rooting time with respect to photoperiodic induction. The largest promotive effect is observed when de-rooting coincides with the start of the inductive treatment or, to a lesser extent, when performed before it. De-rooting 24 h after induction has no effect on flowering. The flower-inducing action of de-rooting 24 h before the start of induction is increased by benzylaminopurine (BAP), whether applied simultaneously with de-rooting or 24 h later. At the beginning of darkness, BAP inhibits flowering slightly when applied simultaneously with de-rooting but inhibits it strongly when applied 24 h later. Flowering in plants de-rooted 24 h after induction is inhibited strongly by BAP. Root removal at the beginning of inductive darkness does not change the level of endogenous cytokinins in induced shoot explants, but under continuous light the level of cytokinins in shoot explants decreases during the same period compared with the level in the shoots of intact plants. BAP does not affect the level of endogenous cytokinins in light but causes an apparent increase in induced segments. Thus, two phases of the de-rooting effect and cytokinin treatment may be distinguished: one in which flowering is enhanced by both treatments and which is linked directly to photoperiodic flower induction, and the other in which both treatments are inhibitory to flowering and which is related to morphogenetic events following induction. The time courses of the effectiveness of de-rooting and BAP treatment differ slightly, suggesting that the effect of de-rooting cannot be attributed solely to cytokinin deprivation.