Coordination of plastid and light signaling pathways upon development of Arabidopsis leaves under various photoperiods

Abstract

Plants synchronize their cellular and physiological functions according to the photoperiod (the length of the light period) in the cycle of 24 h. Photoperiod adjusts several traits in the plant life cycle, including flowering and senescence in annuals and seasonal growth cessation in perennials. Photoperiodic development is controlled by the coordinated action of photoreceptors and the circadian clock. During the past 10 years, remarkable progress has been made in understanding the molecular mechanism of the circadian clock, especially with regard to the transition of Arabidopsis from the vegetative growth to the reproductive phase. Besides flowering photoperiod also modifies plant photosynthetic structures and traits. Light signals controlling biogenesis of chloroplasts and development of leaf photosynthetic structures are perceived both by photoreceptors and in chloroplasts. In this review, we provide evidence suggesting that the photoperiodic development of Arabidopsis leaves mimics the acclimation of plant to various light intensities. Furthermore, the chloroplast-to-nucleus retrograde signals that adjust acclimation to light intensity are proposed to contribute also to the signaling pathways that control photoperiodic acclimation of leaves.

Figure 1.

Light Micrographs of Leaf Cross-Sections and Electron Micrographs of Chloroplasts in Col-0 (A) and ntrc (B). Plants were grown under short day (SD) for 4 weeks and under long day (LD) for 3 weeks. Arrows indicate the irregular shape of the ntrc cells. * indicates a plastid-like organelle in ntrc cell. Scale bars: 100 μm for light micrographs and 2 μm for electron micrographs.

Figure 2.

Accumulation of H₂O₂ (A) and Superoxide (B) in Col-0 Leaves Grown under SD or LD Conditions. Accumulation of H₂O₂ and superoxide was detected using DAB (diaminobenzidine; Sigma-Aldrich) and NBT (nitroblue tetrazolium; Sigma-Aldrich) substrates, respectively. Rosettes were excised at the end of the light period, and incubated on Petri dishes containing 0.1 mg ml⁻¹ solution of DAB (pH 3.8) or a 5 mg ml⁻¹ solution of NBT overnight in darkness. In the subsequent morning, the dishes were transferred to growth light (130 μmol photons m⁻² s⁻¹ at 20°C) for 1 h and, thereafter, the rosettes were incubated in ethanol until chlorophyll was bleached.

Figure 3.

Diagrams Depicting the Proposed Mechanisms How Light, Perceived by Chloroplasts and Photoreceptors, Is Mediated to Signals that Interfere with the Morphological Development of Plant and with the Regulation of Anthocyanin Gene Expression. (A) Light perceived by chloroplasts and photoreceptors in mature leaves generates a systemic signal that is crucial for proper morphological development of young leaves. (B) Transfer of plants to an altered photoperiod modifies the redox homeostasis in chloroplasts. Signal directly from PET or mediated by GUN1 is transferred to cytosol by an unknown mechanism. This chloroplast-derived signal may control the expression of anthocyanin genes independently or via the components of the light receptor signaling pathway.