The mystery within an enigma: The Plant Vacuole, edited by R.A. Leigh and D. Sanders

Academic Press, 1997. $59.95 pbk (xxx + 463 pages)ISBN 0 12 441870-8A winter storm in Warren County, Missouri, New Year's Day, 1999. The airport and highways are closed by snow. Sitting at the window of a friend's farmhouse, I read a book from the past. The references cited in most chapters end in 1995, although a few from 1996 appear to suggest the possibility of change in an area which had long been unchanging. Why should a book first published in 1997, a book where the reporting of progress stopped three years ago, be reviewed now? The answer lies in the fact that the publishers have brought it out in paperback. But is the information it contains still meaningful?Look in your favorite botanical textbook at the introductory picture of a plant cell. It will show a rectangular shape (the cell's outline) with a large, empty hole occupying most of the interior – the hole, is of course, the mysterious plant vacuole. The book's title ‘The Plant Vacuole’ provides a clue to its principal weakness through use of the definite article ‘the'. Thus, the volume describes a singular organelle with many functions, and provides a reference source for the history of the often elegant studies in biochemistry and physiology that have helped to elucidate vacuolar functions. However, significant changes have occurred in the field in recent times. The volume was organized and written just as a new concept about vacuoles emerged: the activities attributed to one multifunctional organelle were, in fact, found to be the responsibility of at least two and maybe more separate perpetrators. Storage and lytic vacuoles are separate organelles, with storage vacuoles being unique to plant cells. This concept grew out of research that was published in the period 1995– 1996, just as most chapters of the book were completed. In their chapter on vacuolar storage of proteins, Galili and Herman recognized the significance of these results1xProtein storage vacuoles form de novo during pea cotyledon development. Hoh, B. et al. J. Cell Sci. 1995; 108: 299–310PubMedSee all References, 2xPlant cells contain two functionally distinct vacuolar compartments. Paris, N. et al. Cell. 1996; 85: 563–572Abstract | Full Text | Full Text PDF | PubMed | Scopus (283)See all References and carefully included a consideration of the concept that protein storage and lytic vacuoles might be separate structures. Another valuable chapter, in my view, is Professor Marty's discussion of morphologic studies of vacuole biogenesis, which includes a consideration of how separate types of vacuoles might originate. Marty's preference is for Golgi-associated structures as vacuole precursors, and he includes a selection of electron micrographs to support this, micrographs that would not, to my knowledge, otherwise be available. In contrast, the chapter on molecular aspects of vacuole biogenesis considers only a singular vacuole and it cites articles from the general literature about the period 1994.Perhaps the example that best illustrates the transition between previous concepts of the vacuole, and emerging concepts of functionally distinct vacuole organelles, is provided by the chapter on tonoplast intrinsic proteins (TIPs). The discovery of these proteins was of fundamental importance for subsequent studies of vacuole functions. The authors of the chapter performed a number of excellent studies demonstrating that TIPs could function as aquaporins, a concept that fits well with the need for water transport into and out of vacuoles during processes regulating lumenal osmolarity and cell turgor. There are several different TIP isoforms, and the different isoforms are described as representing gene products that are expressed in a tissue-specific manner. For example, the first to be discovered, α-TIP, was described as a seed-specific isoform (although, interestingly, the original paper documenting its isolation also demonstrated its expression in other tissues). With the benefit of time and more studies, it became clear that α-TIP is not seed-specific, but rather is present predominantly in protein storage vacuole tonoplast, and protein storage vacuoles are most abundant in seeds. That is perhaps the best result that all of us who are scientists can hope for – to discover a fundamentally important molecule that turns out to be even more interesting than it appeared in the beginning. Similarly for vacuoles. A single vacuole, which occupies most of the cell and has a number of different functions, is a well-studied relic. By contrast, different vacuole organelles, which are unique to plant cells and serve to separate storage and digestive functions, are sources for a rich harvest of experiments in the future.