Photosynthetic pigmentation--variegations on a theme.

Plant pigmentation has been of major interest to horticulturists for millennia. The ancient Egyptians, for example, cultivated the madder plant ( Rubia tinctorum ) as a source of dye for the ornamentation of mummies, and tribal peoples living before the Common Era in northern Britain tattooed their skin with indigo dye, a fact recorded by Julius Caesar upon Roman colonization of Britain. The diligence with which Native Americans cultivated many different pigmented maize seeds can even be ascribed to an early systematic foray into plant genetics. During the present century, the chemical industry has largely obviated the exploitation of plant pigmentation, but basic scientists have pursued studies of plant coloring to the extent that the disciplines of plant physiology, biochemistry, development, and genetics have all flourished and, on occasion, converged. Such convergence of experimental disciplines and approaches is perhaps not surprising given the fundamental roles that pigments play in plant life. Certainly one of the most important functions to be effected by plant pigments is the capturing of light energy for photosynthesis. Chief players in this regard are the green chlorophylls, as well as the orange-red carotenoids. Both of these pigment types reside within chloroplasts, which in turn arise from colorless, non-differentiated proplastids. The appearance of green, photosynthetic tissue from dark-grown (etiolated) seedlings can thus provide an excellent system for addressing a wide range of cell biological themes. As an example, the assembly of the photosynthetic apparatus along with the performance of the carbon reduction cycle within the chloroplast requires the coordinated expression of genes residing Photosynthetic Pigmentation—Variegations on a Theme