SWEET transporters of Medicago lupulina in the arbuscular-mycorrhizal system in the presence of medium level of available phosphorus.

Arbuscular mycorrhiza (AM) fungi receive photosynthetic products and sugars from plants in exchange for contributing to the uptake of minerals, especially phosphorus, from the soil. The identification of genes controlling AM symbiotic efficiency may have practical application in the creation of highly productive plant-microbe systems. The aim of our work was to evaluate the expression levels of SWEET sugar transporter genes, the only family in which sugar transporters specific to AM symbiosis can be detected. We have selected a unique "host plant-AM fungus" model system with high response to mycorrhization under medium phosphorus level. This includes a plant line which is highly responsive to inoculation by AM fungi, an ecologically obligate mycotrophic line MlS-1 from black medick (Medicago lupulina) and the AM fungus Rhizophagus irregularis strain RCAM00320, which has a high efficiency in a number of plant species. Using the selected model system, differences in the expression levels of 11 genes encoding SWEET transporters in the roots of the host plant were evaluated during the development of or in the absence of symbiosis of M. lupulina with R. irregularis at various stages of the host plant development in the presence of medium level of phosphorus available for plant nutrition in the substrate. At most stages of host plant development, mycorrhizal plants had higher expression levels of MlSWEET1b, MlSWEET3c, MlSWEET12 and MlSWEET13 compared to AM-less controls. Also, increased expression relative to control during mycorrhization was observed for MlSWEET11 at 2nd and 3rd leaf development stages, for MlSWEET15c at stemming (stooling) stage, for MlSWEET1a at 2nd leaf development, stemming and lateral branching stages. The MlSWEET1b gene can be confidently considered a good marker with specific expression for effective development of AM symbiosis between M. lupulina and R. irregularis in the presence of medium level of phosphorus available to plants in the substrate.

Sugar transporters of the SWEET family and their role in arbuscular mycorrhiza.

Plant sugar transporters play an essential role in the organism's productivity by carrying out carbohydrate transportation from source cells in the leaves to sink cells in the cortex. In addition, they aid in the regulation of a substantial part of the exchange of nutrients with microorganisms in the rhizosphere (bacteria and fungi), an ty essential to the formation of symbiotic relationships. This review pays special attention to carbohydrate nutrition during the development of arbuscular mycorrhiza (AM), a symbiosis of plants with fungi from the Glomeromycotina subdivision. This relationship results in the host plant receiving micronutrients from the mycosymbiont, mainly phosphorus, and the fungus receiving carbon assimilation products in return. While the eff icient nutrient transport pathways in AM symbiosis are yet to be discovered, SWEET sugar transporters are one of the three key families of plant carbohydrate transporters. Specif ic AM symbiosis transporters can be identif ied among the SWEET proteins. The survey provides data on the study history, structure and localization, phylogeny and functions of the SWEET proteins. A high variability of both the SWEET proteins themselves and their functions is noted along with the fact that the same proteins may perform different functions in different plants. A special role is given to the SWEET transporters in AM development. SWEET transporters can also play a key role in abiotic stress tolerance, thus allowing plants to adapt to adverse environmental conditions. The development of knowledge about symbiotic systems will contribute to the creation of microbial preparations for use in agriculture in the Russian Federation.

[Alteration in the Expression of Genes Encoding Primary Metabolism Enzymes and Plastid Transporters during the Culture Growth of Chlamydomonas reinhardtii].

In a mixotrophic Chlamydomonas reinhardtii culture, the expression levels of genes encoding primary metabolic enzymes and chloroplast plastid transporters were analyzed. For the majority of the genes studied, their expression levels decreased as they approached the final stages of culture growth. During the period of exponential growth, the expression profiles changed more intensively than during the stationary phase. In the middle of exponential growth, significant changes of mRNA profiles reflected reorganization of metabolism, with an emphasis on the induction of lipid synthesis, accompanied by alterations in carbon fluxes through biochemical pathways and a shift in the energy balance between the plastid and cytosol.

[Development of Arbuscular Mycorrhiza in Highly Responsive and Mycotrophic Host Plant-Black Medick (Medicago lupulina L.)].

The main phases of arbuscular mycorrhiza (AM) development were analyzed in black medick (Medicago lupulina) with Glomus intraradices. Methods of light and transmission electron microscopy were used to investigate AM. The first mycorrhization was identified on the seventh day after sowing. M. lupulina with AM-fungus Glomus intraradices formed Arum type of AM. Roots of black medick at fruiting stage (on the 88th day) were characterized by the development of forceful mycelium. The thickness of mycelium was comparable with the vascular system of root central cylinder. The development of vesicules into intraradical spores was shown. Micelium, arbuscules, and vesicules developed in close vicinity to the division zone of root tip. This might be evidence of an active symbiotic interaction between partners. All stages of fungal development and breeding, including intraradical spores (in inter-cellular matrix of root cortex), were identified in the roots of black medick, which indicated an active utilization of host plant nutrient substrates by the mycosymbiont. Plant cell cytoplasm extension was identified around young arbuscular branches but not for intracellular hyphae. The presence of active symbiosis was confirmed by increased accumulation of phosphorus in M. lupulina root tissues under conditions of G. intraradices inoculation and low phosphorus level in the soil. Thus, black medick cultivar-population can be characterized as an ecologically obligate mycotrophic plant under conditions of low level of available phosphorus in the soil. Specific features of AM development in intensively mycotrophic black medick, starting from the stage of the first true leaf until host plant fruiting, were evaluated. The obtained plant-microbe system is a perspective model object for further ultracytological and molecular genetic studies of the mechanisms controlling arbuscular mycorrhiza symbiotic efficiency, including selection and investigation of new symbiotic plant mutants.

[Analysis of metabolic profile of Chlamydomonas reinhardtii cultivated under autotrophic conditions].

This study presents a metabolite profile analysis of unicellular green alga Chlamydomonas reinhardtii grown under autotrophic conditions at late stages of culture development. Metabolites were identified by gas chromatography coupled to mass spectrometry. Approximately 400 peaks corresponding to individual compounds were distinguished, of which approximately 100 compounds (including saccharides, fatty acids, aromatic compounds, amino acids, alcohols, etc.) were identified. A local database of mass spectra of unidentified compounds was created using MassBank software. Mapping of the metabolomic data with the use of the ChlamyCyc service showed that the identified compounds are involved in various energetic, synthetic, and signaling pathways in Chlamydomonas. The mapping of metabolites by their chemical structure with the use of Cytoscape software, combined with quantitative interpretation, showed that the majority of organic matter was concentrated primarily in the carbon backbones of fatty acids and terpenes, as well as saccharides and structurally similar compounds.

[Alteration of transport activity of proton pumps in coleoptile cells during early development stages of maize seedlings].

Comparative analysis of the transport activity of proton pumps (plasmalemma H+-ATPase, vacuolar H+-ATPase, and vacuolar H+-pyrophosphatase) in the membrane preparations obtained from coleoptile cells ofetiolated maize seedlings (Zea mays L.) was carried out. The highest level ofvacuolar pyrophosphatase activity was observed during the early development of coleoptile cells under growth intensification through the elongation. The role of ATPase pumps of tonoplast and plasmalemma in the transport of hydrogen ions increases during further development. The plasmalemma activity in this process is higher. When the growth stops, the activity of proton pumps becomes significantly lower. Nevertheless, their substrate specificity and sensitivity to proton pump inhibitors do not change, which can be an evidence of physiological significance of pumps in the maintenance of cell homeostasis.

[The shift in plasma membrane H+-ATPase activity in coleoptile cells within maize seedling development].

The activity of plasma membrane H+-ATPase was cytochemically investigated in parenchyma cells of maize coleoptile. The intensity of ATP hydrolysis was determined by deposition of electron density sediment formed by lead and inorganic phosphate. The shift in the enzyme distribution and its hydrolytic activity in the plasma membrane of maize coleoptile cells were revealed within seedling development. The intensity of precipitation was quantified by Image Pro Plus. The maximum precipitation was determined in plasma membrane of coleoptile cells of 4-days-old seedlings. The data obtained coincide with the results of previous biochemical investigation of H+-ATPase hydrolytic activity, provided with purified plasma membrane vesicles. Nevertheless the increase in quantity and(or) activity of the enzyme was observed at the 4th day of seedling development which was characterized by slowing down of growth intensity. The results show the possibility of changes in quantity and distribution of the enzyme in plasma membrane during the differentiation process of cell elongation.