SIGNIFICANCE OF CIRCADIAN GENE-EXPRESSION IN HIGHER-PLANTS

The significance of the circadian clock for living organisms is not fu lly understood. Recent findings demonstrate circadian control of trans cription of quite a number of genes with individual maxima throughout the entire day. Evidence in favor of circadian-clock-controlled transl ation has also been documented. In this article, we want to promote th e idea that in plants the clock functions as a regulator which coordin ates critical cellular processes, such as cell division, nitrate reduc tion, or synthesis of chlorophyll-protein complexes, in such a way tha t the generation of dangerous, oxidative radicals or exposure to harmf ul light is minimized. This has been achieved by plant organisms eithe r by confining gene expression to the dark phase or by a tight coordin ation of different tiers of gene expression during the light phase. Th is leads to the consequence for the researcher that the time of experi mentation needs to be carefully considered and documented. It also fol lows that one might lose important findings if only a particular porti on of the day is investigated.