447 Addresses *Laboratoire de Biologie Cellulaire, Institut National de la Recherche Agronomique (INRA), Route de Saint-Cyr, 78026 Versailles Cedex, France; e-mail: hofte@versailles.inra.fr † Department of Molecular, Cell and Developmental Biology, University of Colorado, Box 347, Boulder, Colorado 80309-0347, USA; e-mail: staeheli@spot.colorado.edu Current Opinion in Plant Biology 2000, 3:447–449 1369-5266/00/$ - see front matter © 2000 Elsevier Science Ltd. All rights reserved. Abbreviations ER endoplasmic reticulum Plant cell biology is a rapidly maturing field, which is cur- rently being joined by an increasing number of research groups. In the past, plant cell biology has remained extremely marginal and often entirely eclipsed by rapid progress in the animal and yeast fields. The identity crisis of plant cell biologists is now coming to an end with recent spectacular technological developments, exemplified by the availability of the complete genome sequence of Arabidopsis thaliana, and the realization that plants have evolved exquisitely specific cellular and biochemical strategies to cope with their unique lifestyle. We have tried to illustrate these technological and conceptual changes in the field of plant cell biology with this non-exhaustive selection of reviews. Living cell analysis One example of the recent technological progress is illus- trated in the review by Cutler and Ehrhardt (pp 532–537), which deals with new possibilities that have been created by the use of green fluorescent protein (GFP) technology in plants. The most important advantage of this technolo- gy is that it allows researchers to label specific compartments and cytoskeletal systems of cells, and to do so in a manner that permits them to subsequently follow the behavior of these structures in living cells with a high degree of temporal and spatial resolution. Also discussed is the use of GFP to actively search for novel features of sub- cellular organization by randomly marking structures with this fluorescent probe. Light-control of plant development and protection against light-induced reactive compounds The autotrophic lifestyle of plants depends on light, not only as an energy source, but also as a critical environmen- tal factor for controlling plant growth and development. Plants monitor their light environment via photoreversible phytochromes, blue light absorbing cryptochromes and UV/B receptors. What has been missing to date is informa- tion on how these light detectors convey their signals to the nucleus to activate/deactivate genes. The article by Nagy and Schäfer (pp 450–454) discusses exciting new findings showing that the light-control of plant develop- ment involves the nucleocytoplasmic partitioning of phytochrome photoreceptors. Regulation of transcription through the sequestration of transcription factors in the cytosol is a recurrent strategy in eukaryotes. Plants have invented a unique variation on this theme by controlling the nuclear import of the photoreceptors themselves. Intriguingly, the nuclear imports of phytochrome A and B show the same fluence rate and spectral dependence as the biological responses that they mediate, suggesting that the specificity of responses controlled by a given phytochrome can be explained, at least in part, by the specificity of its nuclear import. The next challenge will be to understand the regulation of migration into and from the nucleus and, again, genetics will show the way. Although light-mediated growth control mechanisms are instrumental for optimizing plant development in terms of long-term photosynthetic output, plants still have to cope with substantial fluctuations in light intensity during the course of each day. How they cope with energy fluxes that are greater than can be productively utilized by their pho- tosynthetic machinery, and how this machinery is protected from the light-induced production of damaging reactive intermediates and byproducts, is the focus of the article by Niyogi (pp 455–460). As the photosynthetic apparatus can be damaged by excess photons and electrons in many locations, plants have evolved a variety of mecha- nisms for protecting the different parts of the photo- synthetic electron-transport chain. The ‘safety valves’ dis- covered to date include several thermal dissipation mechanisms for removing excess photons, and a number of oxygen-dependent alternative electron sinks. The secretory pathway, vacuoles and aquaporins The biosynthetic membrane systems of the secretory path- way, endoplasmic reticulum (ER) and Golgi apparatus, produce and transport products destined for the vacuoles, the plasma membrane, and the extracellular matrix, the cell wall. Whereas the contribution of Hadlington and Denecke (pp 461–468) emphasizes events that are associ- ated with early ER and Golgi sorting of the soluble proteins of this pathway, the Bethke and Jones review (pp 469–475) deals primarily with the role of prevacuolar compartments in the transport of products to the different Cell Biology Plant cells do it differently Editorial Overview Herman Höfte* and L Andrew Staehelin †