Résumé
Photoacclimation requires a coordinated regulation of both nuclear and organelle gene expression and enzyme activation that enables adjustments in the organism's capacity to utilize light energy. The first step in this response is the ability to sense changes in the light environment. Phytochrome and cryptochrome are examples of sensor molecules that respond to changes in spectral quality; however, a role for these receptors as light quantity sensors in fully differentiated cells has not been demonstrated. The redox status of the plastoquinone (PQ) pool has been implicated as a sensor, regulating nuclear gene expression during long-term acclimation to light intensity. This hypothesis proposes that the signal transduction pathway is initiated via the PQ pool redox status or the “excitation pressure” on Photosystem II (PSII), thereby coupling cellular regulatory pathways controlling gene expression and enzyme activation to the cell's capacity to utilize light energy.