IS THE ROOT EFFECT ON FLOWERING OF CHENOPODIUM-RUBRUM MEDIATED BY CYTOKININS

Root removal enhances flowering in the short day plant Chenopodium rub rum. The extent of this effect depends on the de-rooting time with res pect to photoperiodic induction. The largest promotive effect is obser ved when de-rooting coincides with the start of the inductive treatmen t or, to a lesser extent, when performed before it. De-roofing 24 h af ter induction has no effect on flowering. The flower-inducing action o f de-rooting 24 h before the start of induction is increased by benzyl aminopurine (BAP), whether applied simultaneously with de-rooting or 2 4 h later. At the beginning of darkness, BAP inhibits flowering slight ly when applied simultaneously with de-rooting but inhibits it strongl y when applied 24 h later. Flowering in plants de-rooted 24 h after in duction 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 cy tokinins in shoot explants decreases during the same period compared w ith the level in the shoots of intact plants. BAP does not affect the level of endogenous cytokinins in light but causes an apparent increas e in induced segments. Thus, two phases of the de-rooting effect and c ytokinin treatment may be distinguished: one in which flowering is enh anced by both treatments and which is linked directly to photoperiodic flower induction, and the other in which both treatments are inhibito ry to flowering and which is related to morphogenetic events following induction. The time courses of the effectiveness of de-rooting and BA P treatment differ slightly, suggesting that the effect of de-rooting cannot be attributed solely to cytokinin deprivation.