Changes in the content of endogenous auxins in apical buds ofchenopodium rubrum L. Induced with respect to the endogenous rhythm in capacity to flower

Abstract

The content of endogenous auxins was examined in apical buds ofChenopodium rubrum plants induced by a photoperiodic cycle of 16h darkness and 8h light followed by a dark period of various duration so as to correspond with either maximal or minimal flowering response in the endogenous rhythm in capacity to flower initiated by the photoperiodic treatment. Apical buds of potentially generative plants contained less auxins than apical buds of plants which remained in the vegetative state. Apical buds from plants treated with kinetin (1. 10-3 M) and therefore remaining in the vegetative state showed an auxin level comparable to that of untreated plants exhibiting minimal flowering response irrespective of the duration of the second dark period. Plants cultivated on a sucrose solution (0.6 M) during the second dark period became generative even at the normal minimum of flowering. The auxin content of the apical buds was low, similarly as in untreated plants induced for a period leading to maximal flowering response. On the other hand, apical buds from plants grown on sucrose solution during a dark period leading to the manifestation of maximal flowering response showed a relatively high auxin content comparable to that found in untreated plants which had obtained a more extended induction by three photoperiodic cycles. The results are discussed with respect to the possible role of endogenous auxins in the regulation of the changes in growth correlations occurring in the shoot apex during photoperiodic induction and in the expression of the competence to flower.