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0SYMBIOSIS OF NODULE BACTERIA BRADYRHIZOBIUM JAPONICUM AND SINORHIZOBIUM FREDII WITH SOYBEAN PLANTS ISOLATED FROM SOILS OF UZBEKISTAN
Umarov B.R.
Head of the Biotechnology Lab. Tashkent Research Institute of Vaccines and Serums https://doi.org/10.5281/zenodo.13624207
Abstract. The slow and fast-growing Rhizobia bacteria Bradyrhizobium japonicum and Sinorhizobium fredii were isolated from the experimental fields of Uzbekistan, where rice and soybeans are grown, from the soil andfrom the nodules of soy roots upon repeated inoculation of these bacteria with local soybean varieties, it has been demonstrated that these bacteria form nitrogen-fixing nodules in plant roots and enter into symbiotic activity.
Keywords: bradyrhizobium japonisum and Sinorhizobium fredii, symbiosis, plant microbial interactions.
The soybean plant (Glycine max) is an annual plant in the legume-grain crop family, native to Central Asia. In increasing the solubility of the soybean plant, it is now in agricultural biotechnology that the study of natural populations of nodule bacteria and microsymbionts with legumes is of great importance. The study of the genetic diversity of nodule bacteria in the soils of Uzbekistan is one of the most important tasks of soil microbiology [1]. Soy grain is a product of a valuable legume crop, and in the soils of different regions of Uzbekistan, the population of its microsymbionts (nodule bacteria) is very rich. It is known that the soybean plant can enter into symbiosis with several types of nodule bacteria: the slow-growing Bradyrhizobium japonicum, B. elkanii, B. liaoningense [1] and the fast-growing species Sinorhizobium fredii, Mesorhizobium thianshanense [2].
The formation of the rhizobia Bradyrhizobium japonicum and Sinorhizobium fredii, which are characteristic of the soybean plant in the soils of Uzbekistan, is evidenced by the intensive cultivation of soybean varieties, the richness of soybean bacteria in the soils [3]. Soy rhizobia populations are a very favorable object for studying microevolution processes, as a result of which divergence of soy microsymbionts can occur, which is due to their adaptation to various plant genotypes and new soil and climatic conditions. For several years (2001-2004), the Institute of genetics and Experimental Biology of plants and the scientific research institute of rice farming (2015-2017) studied the spread of soybean bacteria in agrocenoses with different intensity of soybean cultivation in experimental fields. The conclusion of scientific results, carried out in alternating planting of soybeans for 5 years, suggests that local populations of soybeans bacteria were formed in the soils of Central Asia. In plant inoculation (vaccination), soil populations turn out to be very heterogeneous, despite the effectiveness of vaccine strains.
Analysis of the morphological, cultural, physiological and biochemical properties of 20 strains of soy rhizobia isolated from their soils in different regions of Uzbekistan has shown that Bradyrhizobium japonicum and Sinorhizobium fredii bacteria differ significantly from slow and fast-growing symbionts of soy species. The strains Bradyrhizobium japonicum and Sinorhizobium fredii were isolated from soil samples planted in soybean and nodules appearing in soybean roots
at the rice scientific research institute, located in Middle Chirchik district, Tashkent region, 20152016.
It is known that the productivity of legumes depends on the effectiveness of their symbiosis with nodule bacteria, which, among others, is determined by nitrogen-fixing activity, virulence, competitiveness, as well as the complementarity (specificity) of strains. Microsymbiont belongs to a particular plant species. In plant and bacterial symbiosis, the use of active strains as vaccines provides intensive fixation of nitrogen from the atmosphere, stimulates photosynthesis and, as a result, leads to an increase in plant productivity [4].
The use of rhizobia strains for inoculations is especially important when growing legumes in new areas where the soil lacks the necessary microsymbionts. For example, when trying to grow soybeans (Glycine max) grains in some geographical zones of Uzbekistan, the roots of the plant are practically not formed. Studies have shown that vaccine strains have a strong role in soil adaptation processes, the effects of maxillary or aboriginal strains in that soil. These genes have gene lines belonging to the Rhizobium that promote the development of symbiosis between the plant and rhizobia. When planting seeds, their inoculation is associated with the activation of selected strains, future fruiting, competition of these strains with other strains, and hsp-genes in the plant genome. Activation of plant and bacterial microsymbionts begins. When plants are vaccinated for the second year, under soil conditions, the activity, competitiveness of vaccine strains, the activation of hsp-genes in the plant genome lead to the active development of microsymbionts.
Conducted experiments have shown that vaccine strains have had a significant positive effect on plant development, increased number of nodules significantly increased dry weight of plants, increased total nitrogen content and seed productivity [4], and had a significant positive effect on plant development, leading to an increase in total nitrogen content in the soil. The low nitrogen content in the soil allows these natural, rhizobia bacteria to enter symbiosis with legumes to develop without the plant receiving mineral nitrogen from the outside. Symbiotic nodules are formed in the roots of plants, which are easily settled by nitrogen-fixing bacteria. Nodule cell surface receptors SYMRK (symbiosis receptor-like kinase) are responsible for transmitting a symbiotic signal from rhizobia perception to nodules formation [5].
The mechanism of activating receptors consists in serving as a catalyst for the symbiotic relationship between legume and nitrogen-fixing bacteria. In the process of symbiosis, free nitrogen in the atmosphere is converted into ammonia (NH3) as a result of chemical reactions in the stem cells and assimilated into the composition of organic compounds. In this, amino acids (protein monomers), nucleotides (DNA and RNA monomers, as well as the most important energy-enriched molecule, ATF), vitamins, flavones and phytohormones are formed. Due to the reduced need of atmospheric nitrogen for nitrogen fertilizers in representatives of the legume family for the cultivation of agricultural crops, the ability of symbiotic nitrogen fixation is characterized, in addition, the high content of nitrogen forms available to the plant in the soil (nitrate (NO3) and ammonium (NH4) prevents the development of nodules in the soil, since symbiosis formation for the plant will not be practical.
The energy that is needed and involved in nitrogen absorption in the tissues is generated by the oxidation of sugary substances from the leaves (photosynthetic products) "Malate", sucrose, splitting of high-quality products, symbiotic bacteria as a source of hydrocarbons. Atmospheric nitrogen reduces the oxygen level in the atmosphere. In this regard, legumes (Fe) contain
legoglobin, an oxygen-binding protein containing iron. Legoglobin (leghemoglobin) is a nodule of hemoglobin found in the tissues of legumes, giving them a red color. Leghemoglobin helps transfer oxygen to symbiosomes containing nitrogen fixing bacteria for their respiration. Leghemoglobin, on the other hand, performs buffer functions by binding excess oxygen, suppressing the catalytic activity of nitrogenase. Legoglobin used in cell respiration is similar to animal myoglobin, which is used to facilitate the distribution of oxygen [6].
Thus, in symbiosis between legumes and legume bacteria, two global biochemical processes are combined - nitrogen fixation and photosynthesis, which normalize the nitrogen-carbon balance of the plant organism. Nodule bacteria perform an ecological niche for the placement of rhizobia, a structural basis for the exchange of metabolites in the structure of two organs, as well as a complex of interconnected functions that provide control over the number and physiological activity of bacteria. From the data it can be concluded that in increasing the effectiveness of soy cultivation in different ecological conditions of Uzbekistan, it is recommended to choose the most genotypic suitable strains of Bradyrhizobium japonicum and Sinorhizobium fredii strains of rhizobia, in which plants developing complementary relationships for each crop variety may play an important role in increasing the fertility of soils.
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