Ion Transport In Plant Cells And Tissues

Ion transport - introduction and general principles; Cell membranes; Mitochondria; Chloroplasts; Algal cells; Storage tissues; Excised roots; Long-distance transport in roots; Whole plants; Halophytes; Salt glands; Stomata.

In the first part (Part A) of this volume on transport, there was an emphasis on the processes occurring at the membranes bounding the cells. It was convenient to distinguish active and passive processes of transport across the membranes, and to recognize that certain transport processes may be regulated by internal factors in the cells such as cytoplasmic pH, concentrations of ions, of malate or of sugar in the vacuoles, or the hydrostatic pressure. Cells in tissues and organs show the same kinds of properties as individual cells, but in addition there can be cell to cell transport related to the organization of the tissue. Firstly cells within a tissue are separated from the external solutions by a diffusion path comprising parts of the cell walls and intercellular spaces; more generally this extra-cytoplasmic part of the tissue has been called the apoplasm. A similar term is "free space". Secondly, the anatomy of cells in tissues seems to allow some facilitated, local transport between cells in a symplasm. Entry into the symplast and subsequent transport in a symplasmic continuum seems to be privileged, in that ions may not have to mix with the bulk of the cytoplasm and can pass from cell to cell in particular cytoplasmic structures, plasmodesmata. In Chara plants, this kind of transport is found operating across the multi-cellular nodes as the main means of transport between the long internodal cells.

In the first part (Part A) of this volume on transport, there was an emphasis on the processes occurring at the membranes bounding the cells. It was convenient to distinguish active and passive processes of transport across the membranes, and to recognize that certain transport processes may be regulated by internal factors in the cells such as cytoplasmic pH, concentrations of ions, of malate or of sugar in the vacuoles, or the hydrostatic pressure. Cells in tissues and organs show the same kinds of properties as individual cells, but in addition there can be cell to cell transport related to the organization of the tissue. Firstly cells within a tissue are separated from the external solutions by a diffusion path comprising parts of the cell walls and intercellular spaces; more generally this extra-cytoplasmic part of the tissue has been called the apoplasm. A similar term is "free space". Secondly, the anatomy of cells in tissues seems to allow some facilitated, local transport between cells in a symplasm. Entry into the symplast and subsequent transport in a symplasmic continuum seems to be privileged, in that ions may not have to mix with the bulk of the cytoplasm and can pass from cell to cell in particular cytoplasmic structures, plasmodesmata. In Chara plants, this kind of transport is found operating across the multi-cellular nodes as the main means of transport between the long internodal cells.

The study of solute transport in plants dates back to the beginnings of experimental plant physiology, but has its origins in the much earlier interests of humankind in agriculture. Given this lineage, it is not surprising that there have been many books on the transport of solutes in plants; texts on the closely related subject of mineral nutrition also commonly address the topic of ion transport. Why another book? Well, physiologists continue to make new discoveries. Particularly pertinent is the characterisation of enzymes that are able to transport protons across membranes during the hydrolysis of energy-rich bonds. These enzymes, which include the H + -A TPases, are now known to be crucial for solute transport in plants and we have given them due emphasis. From an academic point of view, the transport systems in plants are now appreciated as worthy of study in their own right-not just as an extension of those systems already much more widely investigated in animals. From a wider perspective, understanding solute transport in plants is fundamental to understanding plants and the extent to which they can be manipulated for agricultural purposes. As physiologists interested in the mechanisms of transport, we first set out in this book to examine the solutes in plants and where are they located. Our next consideration was to provide the tools by which solute movement can be understood: a vital part of this was to describe membranes and those enzymes catalysing transport.

Ion Transport in Plants covers knowledge about ion transport in plants. The book discusses ultrastructural localization; formalism and membrane models; and membrane resistance and H+ fluxes. The text also describes ?+ fluxes in cells and organelles; Na+-?+ transport and ionic relations of the halophytes; and Cl- transport in vesicles. The ion transport in roots and the symplasm is also considered. Botanists, biochemists and biologists will find the book invaluable.

Life presumably arose in the primeval oceans with similar or even greater salinity than the present ocean, so the ancient cells were designed to withstand salinity. However, the immediate ancestors of land plants most likely lived in fresh, or slightly brackish, water. The fresh/brackish water origins might explain why many land plants, including some cereals, can withstand moderate salinity, but only 1 – 2 % of all the higher plant species were able to re-discover their saline origins again and survive at increased salinities close to that of seawater. From a practical side, salinity is among the major threats to agriculture, having been one of the reasons for the demise of the ancient Mesopotamian Sumer civilisation and in the present time causing huge annual economic losses of over 10 billion USD. The effects of salinity on plants include osmotic stress, disruption of membrane ion transport, direct toxicity of high cytoplasmic concentrations of sodium and chloride on cellular processes and induced oxidative stress. Ion transport is the crucial starting point that determines salinity tolerance in plants. Transport via membranes is mediated mostly by the ion channels and transporters, which ensure selective passage of specific ions. The molecular and structural diversity of these ion channels and transporters is amazing. Obtaining the detailed descriptions of distinct ion channels and transporters present in halophytes, marine algae and salt-tolerant fungi and then progressing to the cellular and the whole organism mechanisms, is one of the logical ways to understand high salinity tolerance. Transfer of the genes from halophytes to agricultural crops is a means to increase salt tolerance of the crops. The theoretical scientific approaches involve protein chemistry, structure-function relations of membrane proteins, synthetic biology, systems biology and physiology of stress and ion homeostasis. At the time of compiling this e-book many aspects of ion transport under salinity stress are not yet well understood. The e-book has attracted researchers in ion transport and salinity tolerance. We have combined our efforts to achieve a wider, more detailed understanding of salt tolerance in plants mediated by ion transport, to understand present and future ways to modify and manipulate ion transport and salinity tolerance and also to find natural limits for the modifications.