Membranes separate the interior medium from the exterior. Obviously, separation does not mean isolation and the membranes, as we can see them at present, act as selective filters across which different types of compounds such as salts, waste, nutriments, nucleotides, etc are transported. Depending on the molecule to be transported several ways can be used. How nucleotides are transported through the thylakoid membranes to the lumen and used in the chloroplast is the aim of the chapter by Drs. Spetea and Thuswaldner, while that of Drs. Paulilo and Falkenkrog reviews the composition of nuclear pores that mediate all the traffic between the nucleus and cytoplasm. In which ways, during evolution, the first cells were formed and how the different compartments appeared remain as tremendously exciting questions, but so far unsolved in many cases. Several theories have been proposed.
The best known is that proposed by Margulis (1970), according to which an ancestral anaerobic prokaryote would become able to ingest solid particles such as other prokaryotes. In some cases the ingested bacteria continued to live and have evolved to give different types of membranes that eukaryotic cells contain today. This theory, also called the endosymbiotic theory, explains the origin of both the chloroplasts and the mitochondria, two major organelles of plant cells. More recently, another symbiotic theory has been proposed by Martin and Müller (1998) to explain the origin of mitochondria. While the contribution by Dr. Bizanz and collaborators traces back the unexpected fate of plastids in today's prokaryotic parasites of animal cells, the chapters by Drs. Solymosi and Schoefs, Dr. Chamarovsky and collaborators and, Dr. Rohacek and collaborators are dedicated to the biogenesis and functioning of the chloroplast membranes. The way of differentiation of the other organelles and cell compartments remain so far as unanswered questions. The search for analoguous compartments in lower organisms may provide the first elements of an answer.
the chapter by Dr. H. Guo enters in this frame and offers a good example for the existence of a putative, so far unrevealed compartment analogue to the higher plant vacuole in cyanobacteria. The plant cell turgor is maintained thanks to the functioning of two typical compartments of plant cells i.e. the cell-wall and the vacuole, but these compartments play other important roles in plant physiology. The chapters by Dr. El Gharras and Dr. Martinez on the accumulation of betalain pigments in vacuoles and strawberry cell-wall softening, respectively, illustrate these aspects of the field. Even if plant cells are surrounded by a thick and rigid cell-wall, their interior is highly dynamic: the organelles are able to move. The contribution by Dr. Foissner analyzes the dynamic of mitochondria in Chara internodal cells. In contrast to animals, plants cannot escape from adverse conditions. Consequently, they have developed strategies to survive to biotic or/and abiotic stresses.
In this book the description of the answers of plants to several stresses are the aim of some chapters. While the contribution by Dr. Ben Khaled and collaborators reports on the peroxidase activity in palm plantlets inoculated with arbuscular mycorrhiza fungi in the presence of biocontrol agents, the chapter by Dr. Dumas-Gaudot and collaborators, describes the modifications in the protein composition occuring during the differentiation of the arbuscules. The formation of the arbuscule is accompanied by a redistribution of the colonized root cell organelles around the arbuscule and by a dramatic change in the plastid metabolism allowing them to produce secondary metabolites, including secondary carotenoid and apocarotenoid molecules (chapter by Dr. Fester). Abiotic stresses, such as nitrogen deficiency, are also able to trigger the production of secondary carotenoids. Dr. Lemoine and collaborators review such a strategy in green algae. Because secondary carotenoids are usually high added value compounds, the knowledge about the functioning of the different compartments in such a production is also of great importance for the economic side of plant science s.l.
How chloroplasts cope with heavy metals is discussed in the chapter by Dr. Poirier and collaborators. During the last years, new technical tools such as confocal imaging became more popular. Their use revealed the presence of new compartments, sometimes being divided into subtle sub-compartments. The intention of this book is to bring together a serie of outstanding contributions dealing with the biosynthesis, content, distribution, function, and physiology of various plant cell compartments. By combining the major contributions in this book, I wished to contribute to the propagation of the recent developments in plant cell biochemistry and physiology, to the discovery of the wonderful plant world and, also, to mutual exchange of ideas. Without the excellent work of the different authors, who have taken great care to present an up-to-date review of their field and 'Research Signpost' as the commercial editor, this book could not have been produced. I wish to dedicate this book to the different mentors in Belgium, Czech Republic and France, who showed me the scientific way and, also to my wife for her everlasting support to me.
Kerala, India: Research Signpost , 2008. 104-149 p.