The Shoot Apex as a Marker of the Responsivity to Photoperiodic Treatment Inducing Flowering of Chenopodium rubrum L.

Two maxima in flowering response to one inductive dark period of 13 h were found in the short day plant Chenopodium rubrum within three weeks of cultivation under continuous illumination either in vitro or in vivo. These maxima correlated with the number of leaf primordia and their relation to the size of the apical meristem. The first maximum in flowering responsivity corresponded with the stage when primordia of the second leaf pair had not yet overtopped the apical meristem, the second one when the primordia of the fourth leaf overgrew the meristem. Maximum responsivity to flowering reached by a mother plant was reflected in explants derived from it. The above morphological markers of responsiveness to floral induction were not linked to plant age and/or to general growth habit. The explants flowered only when part of the stem was present.