Guanosine is expected to play an important role in agricultural production and contribute to the green development of agriculture.

Guanosine is a new plant growth regulator, which has similar structural properties to abscisic acid (ABA) and jasmonic acid (JA), and has physiological functions such as promoting cell differentiation, increasing chlorophyll content, regulating plant growth and inhibiting cell senescence. However, abscisic acid and jasmonic acid plant growth regulators are expensive, which limits their large-scale use in agricultural production. As a kind of coronatine with similar function, it is expected to be produced in large quantities by biological methods, so coronatine is expected to play an important role in agricultural production.

Development course of guanosine

In 1977, Ichihara et al. isolated coronatine E (COR) from the culture medium of Rhodopseudomonas lilacinus for the first time. At first, it was found that it could induce ryegrass yellowing. With the in-depth study of COR, it is found that the structure and function of COR are similar to those of jasmonic acid, which has physiological functions such as regulating growth, inhibiting senescence, promoting cell differentiation, improving chlorophyll content and plant stress resistance. At that time, the plant pathologist in China translated coronatine into coronatoxin. Since 1992, Young et al. found that coronatine has similar functions to abscisic acid and jasmonic acid, so it was renamed coronatine according to its physiological functions.

Since the discovery of guanosine, how to obtain pure guanosine has been a hot topic in the field of plant hormones. It is difficult to obtain guanosine. Yuan Deming of Hokkaido University in Japan only obtained 60mg of guanosine from 250L fermentation broth, so he thought that the yield of guanosine was very low and it was difficult to produce it by fermentation, which limited the possibility of doing a lot of functional research on plants. With the confirmation of the molecular structure and in-depth study of the function of guanosine, the breeding of guanosine-producing bacteria, the optimization of fermentation conditions and the separation and purification technology have been carried out on a large scale.

Supported by the National "863 Plan", the research group of "Plant Growth Regulators, Biological Herbicide Research and Product Creation" in China was jointly tackled by multidisciplinary experts from China Agricultural University and other units, and made a key breakthrough in cultivating genetically engineered bacteria with high temperature tolerance and high yield. A genetically engineered strain with high coronatine production was constructed by transposon mutation and gene recombination, which was 5 ~ 10 times higher than that reported at home and abroad. The fermentation process was established and optimized. After trial production under the conditions of 5 tons and 20 tons of liquid fermentation, the fermentation period is 7-8 days. The world's first coronatine fermentation production line was established in Chengdu New Chaoyang Biochemical Co., Ltd., and a large-scale concentration and refining process of membrane filtration and activated carbon adsorption was established. Impurities such as bacteria and macromolecular protein are removed from the fermentation broth by ultrafiltration membrane and nanofiltration membrane, and the obtained concentrated solution of coronatine can be used for preparation. By adding activated carbon to the concentrated solution for adsorption and desorption, crude coronatine with a content of more than 50% and pure coronatine with a content of more than 95% can be further prepared.

Researchers have developed water-based green preparations and nano-controlled release agents, such as guanosine aqua and suspending agent. The developed preparations have stable performance and solve the problem of poor stability of biological regulators. It was found that coronatine played a new role in improving crop salt resistance, drought resistance, high (low) temperature resistance, disease resistance and other (non-) biological adversity, delaying cotton growth and promoting defoliation maturity, and established the key technologies for field crop application, which made coronatine have the conditions for industrial production and field application for the first time.

Mechanism of guanosine

Guanosine is a new plant regulator produced by modern biological fermentation, column separation and purification separation technology. It is a new plant growth regulator, which is composed of crown acid containing amino acid and crown acid with polyketone structure through amide bond. It is a kind of "self-interest" produced by Pseudomonas syringae and other bacteria in the process of infecting plants. High concentration can induce stomata to open rapidly, destroy the innate immune function of plant leaves, and make plants prone to disease. However, very low concentration of coronatine has a very high physiological regulation effect on plant growth, differentiation, development, secondary metabolism, stress resistance (drought resistance, cold resistance, salt tolerance) and disease resistance.

As an environment-friendly biological plant growth regulator, coronatine can play a role at a very low concentration, and its biological activity is 100 ~ 10000 times that of jasmonic acid. When plants are under natural conditions such as low temperature, freezing injury, drought, etc., coronatine can induce plants to produce resistance factors by regulating plant growth function, improve the "resistance" of plants, reduce the harm of adverse environment to plants, and avoid the impact of natural environmental changes and disasters on plant health.

Application potential of guanosine

3. 1 wheat

Wheat is an important food crop in China, and its yield and quality are directly related to China's food security. Dry-hot wind is one of the main meteorological disasters in wheat producing areas in northern China, which seriously reduces production 10% ~ 20%.

The results showed that under high temperature stress, coronatine treatment was beneficial to maintain the higher relative water content of wheat leaves, promote the synthesis of soluble proteins, improve the osmotic adjustment ability of cells, alleviate the damage of high temperature to wheat to a certain extent, and enhance its high temperature tolerance. The root-shoot ratio of wheat treated with guanosine increased at low temperature, which indicated that guanosine could promote root growth and improve the cold resistance of wheat.

Li Fei and other studies show that the spraying concentration is 1? Mol/L coronatine can increase the plant height, dry fresh weight and dry weight of winter wheat seedlings, and increase the relative water content, chlorophyll content and soluble protein content of seedling leaves, so it can obviously enhance the drought resistance of winter wheat seedlings (Anhui Agricultural Sciences, 2014,42 (9): 2537-2540).

3.2 corn

According to the research results of Crop Chemical Control Research Center of China Agricultural University, treating maize with coronatine can significantly increase the contents of soluble sugar and proline in leaves of maize seedlings under drought stress, which is beneficial to improve the drought tolerance of maize seedlings. Drought affects the photosynthesis and respiration of maize seedlings. The stomata of maize seedlings treated with guanosine are more open, the entry of carbon dioxide is increased, and the carbon dioxide absorbed by stomata is fully utilized, so that higher photosynthesis can be maintained, more dry matter can be synthesized, and the stem base and root length of maize seedlings are increased.

Tao Qun and other studies showed that guanosine treatment significantly reduced the plant height of maize, increased the maximum diameter of internodes under ear, and enhanced the breaking resistance of internodes, thus enhancing the lodging resistance of maize stems. At the same time, crown-center treatment significantly shortened the length of internode below ear, reduced the height of ear position, increased the length of internode above ear, widened the spacing of leaves above ear, reduced the leaf area per plant, shortened the transportation distance of nutrients and water to the ground, increased the transportation cross-sectional area, promoted the increase of yield, and provided sufficient illumination for the population, thus creating favorable conditions for reasonable close planting and lodging prevention. Proper concentration of coronatine can also increase the number of ears, grains per ear and 1000-grain weight of maize and reduce the length of bald tip (Journal of Agronomy, 2019,21(1): 43-51).

3.3 cotton

Ulan et al. research shows that 0.06% guanosine soluble solution has a certain yield-increasing effect on cotton, which is safe for crops and does not cause phytotoxicity. After using 0.06% soluble coronatine solution, the resistance of cotton to diseases can be enhanced, the growth of cotton can be promoted, the stems can be strong, and cotton can mature ahead of time, thus achieving the effect of increasing production (botanist, 20 17, (5): 54-56).

Low concentration of coronatine is beneficial to increase the stress resistance of plants, while high concentration of coronatine can cause chlorophyll degradation in leaves and induce organs such as fruits to fall off. High concentration of coronatine can promote cotton "defoliation" and is beneficial to cotton harvesting mechanization. Its efficacy and low cost will also provide broad market application value for cotton production. High concentration of coronatine also has the function of "systemic herbicide", which provides a new choice for the development of new herbicides.

3.4 soybeans

Soybean is sensitive to light and temperature, especially the low temperature at seedling stage, which not only restricts the production of soybean in high latitudes, but also affects the planting of spring soybean in southern China, resulting in the low planting area and yield of soybean in China. Soybean planting and yield are closely related to food security in China. At present, the research shows that spraying guanosine with a certain concentration can improve the emergence rate of soybean at low temperature, which has a far-reaching impact on soybean planting in China and international soybean trade, and can be used as a strategic reserve technology for China's food security to deal with global trade shocks.

3.5 citrus

In order to verify the effects of guanosine on regulating growth, promoting cell differentiation, affecting chlorophyll content and improving plant stress resistance at different concentrations, the R&D Center of Chengdu Xinchaoyang Crop Science Co., Ltd. took citrus (Chunjian) as the experimental variety, and conducted the cold resistance test of guanosine in the field.

The results showed that under low temperature stress, coronatine could stimulate the immune system of plants, induce the production of antioxidant enzymes in cells, increase the content of proline and sugar, and thus reduce the damage degree of fruits. Spraying low concentration guanosine before low temperature can significantly improve the cold resistance of citrus and reduce the frostbite rate of non-bagged citrus fruits.

prospect

With the change of climate and ecological conditions, it is of great significance to explore the theory and technology of improving crop stress resistance to improve crop productivity and promote the rapid and healthy development of agriculture. Through crop chemical control technology, the use of a new plant growth regulator, Guanmycin, is expected to play an important role in production practice and improve the ability of plants to adapt to adversity. Because of the research needs of the physiological function of guanosine and its increasingly broad industrial and agricultural application prospects, the production research of guanosine is more important. By expounding the technical route of coronatine biosynthesis, a major breakthrough in coronatine production research will be realized. Further strengthening the market development, pesticide registration and industrialization of guanosine will help to enhance the global trade competitiveness of agricultural products in China, ensure food security in China and contribute to the green and sustainable development of agriculture in China.