Plant cells keep a chloride pump on standby to quickly turn it on when the surrounding salt levels get too high.
For any living cell, excess salt is harmful: salt ions affect the functioning of proteins, biochemical reactions, the electrochemical properties of cell membranes, etc. If there are too many salts in the environment, the cell loses water, which rushes out due to the concentration gradient; if, on the contrary, the intracellular environment is saltier, the cell risks being overfilled with water coming in from the outside and simply bursting. In other words, every living organism must be able to monitor the balance of salts in its own cells. For plants, this task is perhaps more important than for anyone else: being immobile, they cannot change their habitat if the soil around them has become too saline.
Salt ions enter the cell together with other substances, and the most obvious solution here is to acquire ion pumps, or ion channels, that would pump out excess salt. Such pumps are operated by specialized membrane proteins, of which there are many varieties. There are many of them because different salt ions differ from each other in some properties, so the pump proteins have to specialize in one or another ion or group of ions, in one or another method of ion exchange. In the case of plants, the pumps that deal with positively charged ions – cations – have been studied quite well. But less is known about the ways in which the plant cell gets rid of negative ions – anions. That is, if we take ordinary table salt, then we know much more about the travels of the sodium ion through the membrane of the plant cell than about the travels of the chloride ion.
Recently, many studies have begun to appear devoted to the so-called plant chloride channels (CLC). Their molecular structure is known; it is also known that their analogues are found in literally all kingdoms of living nature. At the same time, despite the fact that they are called chloride channels, many of them do not deal with chloride ions at all, but conduct some other compounds through membranes. Employees National University of Singapore studied one such protein called AtCLCf. It really does work as a chloride pump, and interestingly, plants keep it ready-made in the Golgi apparatus. This is the name given to the system of intracellular membranes that store various substances, including proteins intended for intracellular or extracellular transport.
At normal salinity, AtCLCf sits in the membranes of the Golgi apparatus, fully prepared for work. When salinity increases, the cell moves AtCLCf from the Golgi apparatus to the outer membrane, where it begins pumping out chloride ions, exchanging them for protons. In the article in Nature Communications describes the movements of the chloride pump, which it performs with the help of another, auxiliary protein. Although CLC proteins have been known for some time, and specifically AtCLCf was also known in advance, the entire mechanism turned out to be new to the researchers, so it can be said that they discovered a new salt pump.
The experiments were conducted with a common model object, Arabidopsis thaliana. If nothing interfered with the work of AtCLCf, Arabidopsis easily tolerated increased salinity in the soil. If AtCLCf was not allowed to integrate into the outer membrane, the plants became especially sensitive to excess soil salt. Finally, if Arabidopsis was supplied with an extra copy of the gene that encodes AtCLCf, the plants became more salt-tolerant than usual. Since plants generally tolerate genetic modifications easily, one can try to integrate extra copies of the gene AtCLCf into agricultural crops so that they do not react so sharply to highly saline soils.
As you can see, both the AtCLCf chloride pump and various other pumps work in the roots. But plants do not always try to cope with excess salt directly in the roots. A few years ago, we wrote that in quinoa, salt goes from the roots to the leaves, where there are special salt-accumulating cells, and in these cells, salt is stored in special bubbles, vacuoles, in which it cannot harm the cell itself and its neighbors. And last year, we talked about the leafless tamarisk, which learned to extract benefits from excess salt – with its help, it collects moisture from the air.
Source: www.nkj.ru
