Nucleic acid synthesis and effect of glucose on its kinetics in cotyledons ofChenopodium rubrum l. during photoperiodic induction

Abstract

In cotyledons ofChenopodium rubrum L. polydisperse RNA is synthesized in the region of the low molecular weight RNAs during photoperiodic induction. After short-time labelling the rate of 4s RNA synthesis was always higher in induced plants than in plants having obtained a light-break in the middle of the dark period. When glucose was added to the nutrient medium during the dark period of a single photoperiodic cycle the rate of nucleic acid (NA) synthesis was higher in non-induced plants than in induced ones at the termination of the dark period. In plants induced by two cycles in the absence of glucose the rate of NA synthesis at the termination of the second dark period was higher in induced than in non-induced plants. This difference is due to the differential kinetics of NA synthesis during darkness. In plants induced in the presence of glucose the peak of the rhythm in NA synthesis was advanced by 4 h relative to that found in plants induced in the absence of sugar. Thus, the termination of the dark period coincided with the negative slope of the oscillation in plants induced in the presence of glucose, while in plants having obtained a light-break NA synthesis decreased only slightly after having attained its peak. In plants induced in the absence of glucose the termination of the dark period coincided with the peak in the rhythm in NA synthesis. The rhythm in NA synthesis of the cotyledons during the dark period of an inductive cycle is out of phase with the rhythm in flower initiation.