The information is prepared on the basis of data from the information-analytical system RSF, informative part is represented in the author's edition. All rights belong to the authors, the use or reprinting of materials is permitted only with the prior consent of the authors.

Project titleComplex effect of plant growth-promoting bacteria and molecular weight-fractionated humic acids on plant drought resistance

AffiliationUfa Institute of biology – Subdivision of the Ufa Federal Research Centre of Russian Academy of Sciences,

KeywordsPGPB, humic and fulvic acids, plant hormones, water metabolism, oxidative stress, photosynthesis

Annotation
Water deficiency is one of the main abiotic stress factors that inhibit the metabolic processes of plants, which leads to the suppression of their growth and a decrease in yield. Rhizospheric bacteria have been shown to activate plant growth is shown by (Plant Growth Promoting Bacteria-PGPB). This contributes to increased productivity, including conditions of drought and other adverse conditions (Zhang et al., 2020; Kaushal1 and Wani1, 2015; Vurukonda et al., 2016; Khan et al., 2020). Humic substances such as humic acids, fulvic acids and their salts are also widely used and have a positive effect on plant growth (Canellas et al., 2002; Zandonadi et al., 2010; Ullah et al., 2020). There is a lot of information about the prospects for the joint use of humates and bacteria, in particular, to increase resistance to salinity (Esringü et al., 2016) and pathogens (Shobha and Kumudin, 2012). However, the effects of the combined use of humic substances with bacteria on the drought resistance of plants have been weakly studied, although there are rare studies indicating a positive effect of their combination on plant growth in drought conditions (Alireza P., 2016). The project is aimed at finding ways to increase the resistance of agricultural plants to drought. We propose to study the effects of the combined action of humic acids fractions differing in in molecular weight and structure , as well as growth-stimulating PGP bacteria on plants under drought conditions. To do this, it is assumed: - To fractionate humic substances by solubility (in alkalis and acids) and molecular weight; - To study the effect of different fractions of humic substances on bacterial growth in vitro; - To select PGP bacterial strains for composing mixtures with humic acid fractions that have a favorable effect on plant growth against the background of drought; - To investigate the mechanisms of action of selected combinations of bacteria and humic fractions on the processes increasing the drought tolerance of plants (water relations, photosynthesis, hormonal balance, resistance to oxidative stress). The selection of individual fractions of humic acids and the selection of the most effective combinations with bacteria determines the scientific novelty of the project.

Expected results
Drought, which affects many regions in the world and Russia, leads to a drop in plant yields. Therefore, there is no doubt about the importance and relevance of finding ways to reduce the negative effects of drought on plants. It is expected that the dependence of the action of humic preparations on the growth of bacteria and plants on their composition will be revealed (or the absence of such a dependence might be shown). It is expected that humate fractions and bacterial strains will be identified, the combination of which has a positive effect on the growth of bacteria in vitro and plants under conditions of water scarcity. It is planned to determine what mechanisms (presumably: influence on the hormonal balance of plants, optimization of water metabolism, osmotic regulation and protection from oxidative stress) will stimulate the growth of bacteria under stress under the influence of a combination (composition) of fractions of humic substances and bacteria.

Annotation of the results obtained in 2023
The results showed the ability of a combination of bacteria, humic and fulvic acids to stimulate the growth of wheat plants under conditions of water deficiency (drought from insufficient watering). We have identified probable mechanisms for stimulating plant growth under the influence of their treatment with the bacterial strain Pseudomonas plecoglossicida 2,4-D and fractions of humus components. We analyzed the effect of a combination of bacteria and fractions of humic substances (HS) on plant water metabolism (hydraulic conductivity, water potential, relative water content), as well as the efficiency of photosynthesis, indicators of oxidative stress and hormonal status in plants of bread spring wheat under drought conditions. It was shown that bacteria together with humic acids more effectively stimulated the accumulation of root mass than individually. As a result of drought, plant growth slowed down, but there was a significant increase in shoot length under the influence of bacteria, and higher numbers were observed when bacteria were combined with humates and fulvates. Plants inoculated with bacteria were able to maintain higher relative water content (RWC) in leaves. Hydraulic conductivity decreased under the influence of drought, and increased under the influence of all variants of bacterial treatments. However, an increase in the RWC in the leaves of plants treated with a mixture of bacteria and HS fractions indicates a better supply of water to the leaves. The hydraulic conductivity of plants treated with bacteria was higher than that of untreated plants. Water deficiency led to the accumulation of ABA in leaves, which closes stomata’s, reducing water loss through transpiration. In our case, transpiration decreased under the influence of drought, and treatments did not have a significant effect on it. The results indicate a decrease in oxidative stress in roots (reduction in MDA content) under the influence of bacteria. High levels of reactive oxygen species inhibit the activity of aquaporins. Therefore, reduced levels of oxidative stress in plants (influenced by bacteria) could contribute to the maintenance of aquaporin activity and hydraulic conductivity. It was shown that an increase in the nitrogen index correlated with the chlorophyll content under the influence of the bacterial strain and humic substances. The increase in chlorophyll was most pronounced in plants treated with bacteria and their combination with humates. The growth-stimulating effect of the bacterial strain P. plecoglossicida 2,4-D is explained by the production of auxins and an increase in their concentration in the roots, thereby increasing their mass. HS also increased the concentration of auxins in roots. The additive effect of treatment with humic substances and bacteria could be from an increase in the production of bacterial auxin induced by humic substances, promoting the activation of root growth. The concentration of ABA in plant roots increased in drought conditions. Bacterial treatment (alone or in combination with HS) prevented ABA accumulation caused by water deficiency. The content of cytokinins in the roots of plants growing under drought conditions and treated only with HS increased and was the reason for the observed decrease in their weight. Cytokinin concentration was not increased in the roots of plants treated with a combination of humic substances and bacteria. Thus, the accumulation of root mass in wheat plants was revealed when they were treated with a combination of P. plecoglossicida 2,4-D and HS under drought conditions. It was shown that under conditions of soil water deficiency, bacteria with both humates and fulvates had the same stimulating effect on the growth of shoots and roots and RWC. However, the effect of the humic substance fractions was more noticeable compared to their original preparation. Thus, we have shown the prospects of using a combination of bacterial preparations with HS fractions to increase the growth rate and yield of plants in the long term.

Publications

1. Feoktistova A.V., Timergalin M.D., Chetverikov S.P., Nazarov A.M., Kudoyarova G.R. Effects on Pseudomonas plecoglossicida 2,4-D and Humic Substances on the Growth, Pigment Indices and Concentration of Hormones in Wheat Seedlings Grown under Water Deficit Microorganisms, Microorganisms 2023, 11, 549 (year - 2023) https://doi.org/10.3390/microorganisms11030549

2. Feoktistova A.V., Timergalin M.D., Rameev T.V., Chetverikov S.P. СОВМЕСТНОЕ ВОЗДЕЙСТВИЕ ШТАММА PGPB Pseudomonas plecoglossicida 2,4-D И ГУМИНОВЫХ ВЕЩЕСТВ НА РОСТ, СОДЕРЖАНИЕ ФОТОСИНТЕТИЧЕСКИХ ПИГМЕНТОВ И ФИТОГОРМОНОВ В РАСТЕНИЯХ ПШЕНИЦЫ В УСЛОВИЯХ ЗАСУХИ Агрохимия, АГРОХИМИЯ, 2023, № 9, с. 28–36 (year - 2023) https://doi.org/10.31857/S0002188123090065

3. Timergalin M.D., Feoktistova A.V., Kendjieva A.A., Nazarov A.M., Chetverikov S.P., Kudoyarova G.R. The Effect of Bacterial Treatment in Combination with Humic Substances on Growth, Indicators of Oxidative Stress and Water Relations of Wheat Plants Under Soil Water Shortage RUSSIAN JOURNAL OF PLANT PHYSIOLOGY, - (year - 2023)

Annotation of the results obtained in 2022
Preparations of fulvates and humates were obtained, the source of which was the brown coal of the Tyulgan deposit of the Orenburg region of the Russian Federation. The effect of various fractions of humic substances (total preparations of humates and fulvates and low molecular weight fraction of humates) on bacterial growth in vitro has been studied. The effectiveness of the effect of bacterial strain Pseudomonas рlecoglossicida 2,4-D in combination with fractions of humic substances on plant growth was investigated, using the example of bread wheat seedlings. Both rhizospheric bacteria and humic substances used separately promote plant growth, and we have demonstrated a synergistic effect from their combination. The effect of humic (HA) and fulvic (FA) acids on the growth of bacterial strain P. plecoglossicida 2,4-D in vitro was studied. The effect of this bacterial strain and/or humic substances on the growth of wheat plants under normal conditions and with water deficiency was also evaluated. Although the bacterial strain P. plecoglossicida 2,4-D demonstrated a low ability to use humic substances as the only food source, but with the availability of other nutrients, the growth rate of bacteria increased, due to HA and FA. Humates increased the colonization of roots by bacteria, and this effect was stronger in the case of treatment with humic acid. Activation of plant growth was observed during complex treatment with bacteria and humic substances. Moreover, fulvic acid in combination with the bacterium most stimulated the growth of the shoot, and humic acid with the bacterium – the growth of the root. The latter effect is likely to be beneficial for edaphic stresses. In conditions of water scarcity, the accumulation of fresh mass in wheat plants was revealed when P. plecoglossicida 2,4-D with and humic substances was treated. This can be applied in agricultural practice, since it is known that the growth rate correlates with the productivity of plants.

Publications

1. Feoktistova A.V.,Bakaeva M.D., Timergalin M.D., Chetverikova D.V., Kendjieva A.A., Rameev T.V., Hkudaygulov G.G., Nazarov A.M.,Kudoyarova G.R., Chetverikov S.P. Effects of Humic Substances on the Growth of Pseudomonas plecoglossicida 2,4-D and Wheat Plants Inoculated with This Strain Microorganisms, Microorganisms 2022, 10, 1066. (year - 2022) https://doi.org/10.3390/microorganisms10051066