There is a kind of "pump", which needs no external power, has no noise and is invisible to the naked eye. The place where it "works" is the cell of the plant; What is transported is also very special-it is salt absorbed by plants. Scientists have given it a very special name: Na+ (sodium ion) /H+ (hydrogen ion) antiporter.
The research team led by Professor Zhao Yanxiu and Professor Zhang Hui of Shandong Normal University discovered this protein from Suaeda salsa, and also isolated the full-length cDNA of Na+/H+ antiporter (SsNHX 1) which controls the production of this protein. This discovery has brought new hope to the development of saline-alkali land that has been sleeping for thousands of years.
Why is Suaeda salsa salty?
Suaeda salsa is the most important "fixed resident" on the saline-alkali beach. In autumn, Suaeda salsa is the only bright color on the white saline-alkali beach. This plant that can grow in seawater supports the fragile ecosystem of the Yellow River Delta.
Earlier, Suaeda salsa could only be used as a "ration" for rabbits or insects. During the famine, the victims also depended on it for survival. In recent years, a large number of wild vegetables have been listed, and Suaeda salsa has become a "healthy food".
Suaeda salsa has a unique taste: salty without salt. This phenomenon, which is easily overlooked by ordinary people, has become a major topic for some researchers in Shandong Normal University. They study how plants survive in adversity, aiming at cultivating crop varieties with economic value, and Suaeda salsa is the best research object.
Fresh Suaeda salsa tastes salty, indicating that Suaeda salsa itself contains salt. But where does Suaeda salsa hide the salt?
Saline-alkali land is mostly barren because there is too much salt in the soil. It is difficult for ordinary plants to grow on saline-alkali land. One explanation is that when the salt accumulated in these plants is too high, their roots will reduce their ability to absorb water. Without water, plants can only die.
Plants are made up of cells. From the cellular point of view, when the concentration of salt (mainly sodium ion) in the soil is too high, sodium ion will automatically penetrate into the cytoplasm with low salt concentration through the cell membrane of plants, which will increase the salt concentration in the cytoplasm. Excessive sodium ions will affect the activity of enzymes in cytoplasm, which will lead to difficulties in cell metabolism, thus causing plants to wither and die. This is "salt stress", also known as salt damage.
Therefore, according to the adaptability of plants to soil salt content, plants are divided into "sweet soil plants" and "halophytes". There is an insurmountable "natural barrier" between these two plants, which is generally considered as "soil salt content of 5‰". If it exceeds this barrier, sweet soil plants cannot survive.
Halophytes are also a large family, such as Salicornia, Suaeda salsa and marine plants such as kelp. Both of them are halophytes, but their salt tolerance mechanisms are different. The mechanism of algae and many terrestrial halophytes is secretion. They can secrete the salt absorbed into the body, so the taste is still light after washing.
Suaeda salsa has a unique mechanism. It can absorb salt, even improve saline-alkali land, provide a relatively good environment for the survival and reproduction of other plants, and form a saline-alkali land ecosystem. This characteristic makes people engaged in this field call it a "pioneer plant" in the development of saline-alkali land, but its unique mechanism has not been clearly understood before.
The structure of a cell is similar to that of an egg: the cell wall is like an eggshell with a nucleus (yolk) and cytoplasm (egg white) inside. In the cytoplasm, there is an organ called vacuole, which is also in the cell, floating in the cytoplasm, but it is relatively closed, and its function is similar to a storage room, regulating the balance inside the cytoplasm. If there is anything extra in the cytoplasm that affects the enzyme activity, you can put it here without affecting the enzyme activity in the cytoplasm. The function of vacuole is often ignored by people, and its explanation can not be found in general popular science works.
Shandong Normal University is one of the top ten demonstration projects of sustainable development in our province, and Professor Zhang Hui is the chief scientist of "Comprehensive development and utilization of land resources and demonstration of large-scale production technology of salt-tolerant and seawater-tolerant plants in the Yellow River Delta". He speculated that the salt in Suaeda salsa can only be hidden in the vacuoles of cells, and any other place will affect the life activities of cells.
But the question also arises: if the salt stored in the vacuole is higher than other parts of the cytoplasm, what can transport the salt continuously absorbed by Suaeda salsa to the vacuole?
How does the water pump work?
The activity of life is the movement of protein, and the formation of protein is controlled by genes, which are protein's "designers". Therefore, to explain the unique mechanism of Suaeda salsa, we need to start with genes; From the application point of view, only by capturing this unique gene can biotechnology be used to improve sweet soil crops and cultivate new salt-tolerant plants.
However, the difficulty of this work is also daunting.
Suaeda salsa has at least 50 thousand genes. Finding a specific gene from such a complex system is undoubtedly looking for a needle in a haystack. In the most basic investment, Shandong Normal University, as a local university, has received limited support for scientific research projects, that is to say, their projects have not received strong support from the government.
Zhang Hui said, "We are doing a stupid job."
But they did it without hesitation. 1999, they first constructed the gene library of Suaeda salsa, and began to screen the library and sequence it on a large scale; At the same time, Zhang Quan and other research groups designed another PCR strategy according to the gene sequences of human, yeast and Arabidopsis, and finally successfully cloned the target gene-"full-length cDNA of Na+/H+antiporter (SsNHX 1)", and verified its function in sweet soil plant Arabidopsis. They registered the discovered genes in the "gene bank" and applied for a national invention patent. Recently,
It is worth noting that it has become an international trend to explore new stress-resistant genes in plants by using functional genome strategy, and it is facing international competition. Compared with their counterparts with guaranteed investment and excellent equipment, these researchers have reached the international frontier level and kept pace with their foreign counterparts, although they have no favorable conditions. In fact, they put forward the idea of cloning the above genes of Suaeda salsa and using them in genetic engineering breeding of salt-tolerant crops. At an international seminar in June 1999, the idea was introduced in a paper submitted by Professor Zhang Hui, a research group, but in August, American scientist E? Blumwald was officially published in the American journal Science, and the salt-tolerant transgenic Arabidopsis thaliana was obtained by overexpressing the coding gene AtNHX 1 of Arabidopsis thaliana Na+-H+ antiporter. This progress has enhanced the confidence of the members of the research group. In July 2000, they obtained the full-length sequence of the gene, which was the first time that people successfully isolated the salt-tolerant gene from halophytes. In May, 20001year, they completed the functional verification of genes and launched a series of research on transgenic crops. In June, they applied to the State Patent Office for an invention patent, and in August this year, the State Patent publicized their application.
After understanding this gene, the mechanism of the magic pump hidden in Suaeda salsa is obvious: this pump is a kind of protein with transport function, which will adsorb sodium ions on itself in the cytoplasm, cross the vacuole membrane to reach the vacuole, and then release sodium ions. Vacuolar membrane is different from cell membrane, it does not allow salt and other substances to enter and exit at will, and can only pass under the guidance of transporters. In this way, although the concentration of sodium ions in vacuoles is very high, it ensures that the concentration of sodium ions in cytoplasm is very low. The physiological and metabolic activities of cells are mainly carried out in cytoplasm, so Suaeda salsa will not be harmed by salt. This kind of protein transports salt from low-concentration cytoplasm to high-concentration vacuoles, just like sending water from a low place to a high place, which scientists call "pumping water".
The discovery of this gene means a new way to cultivate salt-tolerant plants, and the commercial value of this discovery is immeasurable.
For a long time, people have been hoping to cultivate salt-tolerant and drought-resistant horticultural plants and crops. However, Chinese and foreign breeding practices have proved that salt-tolerant crops and horticultural plants cannot be cultivated by traditional hybridization methods, while distant hybridization and cell engineering at cell level have few breakthroughs and low success rate due to technical reasons.
Smart readers will ask: If the salt-tolerant sweet soil plants grow the "pump" of Suaeda salsa, will they have the same salt-tolerant function as Suaeda salsa? It is possible in theory, but it needs scientific experiments to prove it.
Let plants grow "pumps", of course, they can't be installed cell by cell, but let plant cells "produce" themselves. As the saying goes, "it is better to teach people to fish than to teach them to fish." The "machine" responsible for producing this "pump" is the gene mentioned above.
Shandong Normal University researchers have carried out a series of studies around their findings: through modern biotechnology, the key genes of salt tolerance of Suaeda salsa were introduced into the genome of Arabidopsis thaliana which is salt-tolerant and drought-tolerant, and transgenic Arabidopsis thaliana was obtained. This new Arabidopsis thaliana can complete its life cycle under the condition of 1/2 seawater irrigation; Under the condition of pot culture, the plants can resume production and bear fruit after rehydration without watering for 15 days, while all the control plants die. Further research found that the salt tolerance and drought tolerance of transgenic Arabidopsis thaliana were greatly enhanced.
Crop genetic engineering and its industrialization are the frontiers of agricultural biotechnology in the world. The first generation is to cultivate insect-resistant and herbicide-resistant plants (such as insect-resistant cotton), the second generation is to cultivate plants with improved quality (such as corn increased in protein), and the third generation is to cultivate stress-resistant plants (salt-tolerant and drought-tolerant plants).
According to the survey, there are nearly 65.438+billion hectares of salinized wasteland in the world, the total area of salinized soil in China exceeds 80 million hectares, and the saline-alkali land in our province is also over 6.5438+0.4 million hectares, with more than 6.5438+0.00 million mu of saline-alkali land newly born every year, which is now barren. We can imagine that if crops and trees with high economic and social benefits grow "pumps" that can pump salt, this vast wasteland will grow golden wheat and lush forests.
A small "water pump" may change the world.