A complex pattern of changes in polysomal mRNA populations is evident in the leaves of Arabidopsis thaliana (L.) Heynh. during photoperiodic induction of flowering

Abstract

Previous studies have indicated that the photoperiodic induction of flowering results in qualitative changes in gene expression in the leaves of the induced plant. However, we obtained different results when leaf tissue was examined at different sampling times after flower induction, thus pointing to the possibility that alterations in gene expression during photoperiodic induction are only transient. We analyzed the composition of mRNA populations in the leaves of the long-day plant Arabidopsis thaliana (L.) Heynh. at various times during photoperiodic induction. Polysomal mRNA populations were assayed during illumination programs consisting of different photoperiodic cycles. Quantitative changes of distinct leaf mRNAs were observed during the time course. The expression levels of most of these mRNAs oscillated in a diurnal or circadian rhythm with respect to the photoperiod. However, no novel mRNA appeared or decreased to undetectable levels during the changes in photoperiod. After the onset of inducing photoperiods, alterations in the phase and amplitude of these oscillations were seen. Various types of oscillation pattern were observed. These changes occurred either very rapidly, within hours after the additional light period began or appeared after the first altered photoperiod was complete. The majority of the changes seen at the beginning of inductive photoperiods were transient and the mRNA levels reverted to the original pattern when the plant was returned to non-inductive photoperiods. In addition, some of these alterations were found to be transient, irrespective of the length of subsequent light periods.