For uncharged solutes non-electrolytes , their movement across the membrane depends upon their concentration gradient i. Therefore, electrical properties of the cell or its Trans membrane potential is very important component of ions transport through membranes. In either case, the transport of solutes across the membrane is called as passive transport if it is along the chemical potential gradient or electrochemical potential gradient for non- electrolytes and electrolytes respectively. When solute transport across the membrane occurs against the chemical potential gradient or electrochemical potential gradient, it is called as active transport and requires additional input of energy Fig.
The movement of solutes into the cytosol through membrane such as plasma membrane or tonoplast is called as influx while their exit from the cytosol is termed as efflux.
These transporter proteins are highly specific with complex structure and different models have been given by scientists to explain their functioning. Ion-channels are trans-membrane proteins which function as selective pores through which ions can diffuse easily across the membrane.
Ion-channels are usually highly specific for one or limited number of ion species.
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. From my distant student days I remember finding other similarly titled books very useful. There was Solute transport in plant cells and tissues (Baker DA and Hall.
The specificity depends upon the size of the pore and density of surface electric charges on its interior lining more than on selective binding of ions. The gates open or close in response to external stimuli that include, i voltage changes, ii light, iii hormone binding and iv ions themselves.
The channel proteins are believed to contain a sensing region or sensor which responds to the appropriate stimulus by changing conformation of channel protein opening the gate. Ions can diffuse through an open channel with rapidity as high as 10 8 s Those channels which allow inward transport of ions i.
Many channel proteins are inducible i. Some slow vacuolar SV channels may be present on tonoplast which allow diffusion of some cations and also anions from vacuole to cytosol.
These trans-membrane transporter proteins do not form pores in membrane, instead they selectively bind the solute to be transported to a specific site on them. After the solute is released from the binding site, the carrier protein reverts back to its original conformation to pick up a fresh solute molecule or ion Fig.
Thus, binding and release of solute through carrier is similar to an enzyme catalysed reaction. Carrier mediated active transport of solutes takes place against the electrochemical potential gradient and requires additional input of energy that chiefly comes from hydrolysis of ATP. As mentioned earlier, the membrane transporter proteins involved in primary active transport of solute are called as pumps. Therefore, it is an electro neutral pump. Electro genic pumps on the other hand, transport ions involving net movement of charge across the membrane.
Therefore, it is an electro genic pump. Therefore, other mechanisms secondary active transport are required for uptake of most of the mineral nutrients. Ion Uptake by Plant Roots.
Transport from Root to Shoot. Transport in the Phloem. Back Matter Pages About this book Introduction 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.
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.
Chloroplast Plasma Xylem bacteria ion transport membrane mitochondria phloem plant plant roots plants plasma membrane roots transport water.