The Photoperiodic Flowering Response in Pharbitis nil

Abstract

Abstract This chapter introduces a mechanism of photoperiodic flowering response in Pharbitis, drawing on the physiological and molecular genetic studies carried out to date. In Pharbitis, a circadian system whose phase is set by lights off through the action of red, far-red, and/or blue light during the light period, controls the photoperiodic flowering response. This circadian system may be distinct from that which controls other circadian rhythms, such as CAB gene expression. This circadian clock determines the phase of one or more clock-controlled genes, which generate a dusk-set activity rhythm in the dark and induce PnFT expression if the dark period is sufficiently long. In this model, one or more clock-controlled genes may be activated specifically in the dark, while red light may directly inhibit such activity during the light period. This mechanism is in contrast to that proposed for Arabidopsis and rice, both of which possess a mechanism for measuring the length of the day in which a clock-controlled gene, whose phase is mainly set by lights on at dawn, is directly activated by light posttranscriptionally.