Intercellular communication in plants. Annual Plant Reviews Vol 16: Fleming AJ. (ed). 2005. Oxford/Boca Raton: Blackwell Publishing/CRC Press. £105.00 (hardback). 280 pp

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Volume 16 of the Annual Plant Reviews series, compiled by Andrew J. Fleming, focuses on intercellular communication in plants. This is an extremely interesting book that extensively covers ten topics related to cell–cell or long-distance communication in plants. The chapters are written in a clear style and they compile the most relevant and up-to-date information in a manner understandable for anybody seriously interested in short- and long-distance intercellular communication. Moreover, besides black-and white illustrations and photographs found in all chapters, there are also six separate colour plates. I highly recommend this book to the wide audience of plant cell biologists, but especially to researchers and postgraduates.

The book starts with a chapter devoted to auxin, currently the most ‘popular’ plant molecule, which is known to affect almost all processes in plants. Besides its well known hormonal status, auxin emerges also as plant morphogen. The authors of this chapter start with Charles and Francis Darwin as their studies with grass coleoptiles, accomplishing phototropic growth responses, lead to the discovery of auxin. Auxin is transported from cell-to-cell via still-elusive mechanisms. The last 6–8 years have witnessed an explosion of new data identifying mutants and proteins relevant for the polar transport of auxin along and across plant organs. However, the exact roles of these proteins, as well as the nature of underlying cellular processes driving the transcellular transport of auxin, still remain unknown. The classical chemiosmotic theory faces difficulties in explaining the inability of auxin molecules, despite their small size (approx. 175 Da), to traverse plasmodesmata that allow free passage for large molecules up to 1000 Da (see chapter 5). Moreover, there are also new data that are at variance with the current version of chemiosmotic theory, including the rapid inhibition of auxin transport with brefeldin A, inhibitor of vesicular secretion, and findings that the inhibitors of auxin transport act rather as general inhibitors of plant endocytosis. To account for all of this, the authors mention as the most exciting possibility a scenario according to which auxin would be exported from cells via secretory processes analogous to vesicular neurotransmitters released at neuronal synapses.

The next chapter deals with emerging roles of peptides in regulation of divisions, growth and wound responses of plant cells. Although peptide-based intercellular signalling is popular in animal/human biology, it was not considered to be relevant for sessile plants lacking mobile cells. As this chapter concludes, we will soon be forced to abandon this popular view as there are striking similarities between animal and plant peptide signalling. The following chapter deals with the emerging roles of RNAs in short- and long-distance cell–cell communication. As this topic is closely related to RNAi technology, this technique is briefly introduced too. Systemic transport of RNP complexes integrates the whole plant body and orchestrates the biological functions of plants. Interestingly, cell–cell transport of RNA molecules is also closely related to viral resistance.

Continuous cell walls provide the plant body with a superstructure interconnecting all cells into a structurally coherent medium, allowing supracellular transport of molecules small enough to penetrate cell-wall pores. In addition to this, fragments of cell wall molecules, especially of pectins and hemicelluloses, serve as paracrine-like intercellular signalling molecules. This provides the focus of chapter 4, written by the editor of the book, Andrew Fleming. The following chapter deals with another supracellular structure of plants, plasmodesmata—representing stable cell–cell channels of plants. It might serve as an introduction to Volume 18 of the same Annual Plant Reviews series, edited by the co-author of this chapter, Karl Oparka. Here it is important to mention that although plasmodesmata are well accepted now, it took more than 80 years to get them accepted by the wide scientific community (Carr, 1976) as they were often regarded as fixation artefacts. Interestingly in this respect, animal cells can also be interconnected via similar, but more delicate and often only temporary, cell–cell channels termed nanotubules (Baluska et al., 2004, Rustom et al., 2004). Hopefully, rapidly developing technologies, especially in respect of in vivo microscopy, will allow reliable assessment of their importance for animal tissues more quickly than was the case with plasmodesmata.

Chapter 6, similar to the subsequent chapters 8 and 9, deals with impacts of intercellular communication on morphogenesis of shoot and root apices (chapters 6, 8), as well as in the leaf epidermis with a particular focus on trichomes (chapter 9). Clavata-based peptide signalling and auxin signalling dominate these chapters. But plant morphogenesis and tissue patterning also rely heavily on cell–cell communication via plasmodesmata and this is highlighted in chapter 7, which discusses the long-distance signalling and mobile molecules underlying floral initiation and development. Recent advances in this field clearly reveal that intercellular communication is of prime importance for transmission of floral stimuli from young leaves to the shoot apical meristem.

The last chapter is devoted to cell–cell signalling networks underlying plant-incompatibility systems. This chapter extensively covers the current state-of-art of this intriguing topic and makes an enthusiatic finale for this ‘tour-de-force’ of intercellular communication in plants.

Overall, this volume is a valuable addition to the preceding volumes of the Annual Plant Reviews series devoted to the plant cytoskeleton (10), polarity (12) and plasmodesmata (18). Perhaps it would have been more comprehensive if it had also included chapters dealing with intercellular communication during embryogenesis and systemic signalling in plants, two fields that have also experienced dramatic developments in the last few years. Nevertheless, this volume makes it clear that intercellular communication emerges as an important topic in plant biology, which will progress rapidly in the future.