Endophytic Bacillus subtilis is a non-pathogenic beneficial bacterium which promotes plant growth and tolerance to abiotic stresses, including drought. However, the underlying physiological mechanisms are not well understood. In this study, the potential role that endogenous salicylic acid (SA) plays in regulating endophytic B. subtilis-mediated drought tolerance in wheat (Triticum aestivum L.) was examined. The study was conducted on genotypes with contrasting levels of intrinsic drought tolerance (drought-tolerant (DT) cv. Ekada70; drought-susceptible (DS) cv. Salavat Yulaev). It was revealed that B. subtilis 10-4 promoted endogenous SA accumulation and increased the relative level of transcripts of the PR-1 gene, a marker of the SA-dependent defense pathway, but two wheat cultivars responded differently, with the highest levels exhibited in DT wheat seedlings. These had a positive correlation with the ability of strain 10-4 to effectively protect DT wheat seedlings against drought injury by decreasing osmotic and oxidative damages (i.e., proline, water holding capacity (WHC), and malondialdehyde (MDA)). However, the use of the SA biosynthesis inhibitor 1-aminobenzotriazole prevented endogenous SA accumulation under normal conditions and the maintenance of its increased level under stress as well as abolished the effects of B. subtilis treatment. Particularly, the suppression of strain 10-4-induced effects on proline and WHC, which are both contributing factors to dehydration tolerance, was found. Moreover, the prevention of strain 10-4-induced wheat tolerance to the adverse impacts of drought, as judged by the degree of membrane lipid peroxidation (MDA) and plant growth (length, biomass), was revealed. Thus, these data provide an argument in favor of a key role of endogenous SA as a hormone intermediate in triggering the defense responses by B. subtilis 10-4, which also afford the foundation for the development of the bacterial-induced tolerance of these two different wheat genotypes under dehydration.

Общеизвестно метаболическое значение йодтиронинов в организме человека и животных. Для растений подобные соединения не описаны, однако, известны эффекты лекарственных растений на функцию щитовидной железы, что предполагает возможность присутствия соединений, аналогичных тиреоидным гормонам в клетках растений. Цель работы - выявление в клетках высших растений биологически наиболее активного представителя йодтиронинов - 3,5,3’-трийодтиронина. Методом иммуноферментного анализа показано, что в тканях корня и стебля проростков фасоли присутствует соединение, взаимодействующее с поликлональной сывороткой к 3,5,3’-трийодтиронину. Установлено, что в клетке выявленное соединение распределено неравномерно: в ядрах клеток его концентрация в 7-10 раз выше, чем в цитоплазме. Наряду с растениями фасоли исследованы 8 случайно выбранных растений, принадлежащих как к двудольным, так и однодольным растениям. Во всех исследованных растениях методом иммуноферментного анализа определено присутствие аналога 3,5,3’-трийодтиронина. Добавление экзогенного йодтиронина - тироксина (3,5,3’,5’-тетрайодтирони-на) при предпосевной обработке семян пшеницы достоверно повысило их всхожесть и привело к значимому увеличению соотношения массы побега к массе корня пятисуточных растений пшеницы при времени замачивания 6 и 12 ч. Вследствие обработки семян пшеницы тироксином в ядрах клеток стебля и корня пятидневных растений пшеницы произошло достоверное снижение концентрации выявленного соединения. Накопление в ядрах клеток и выявленные физиологические эффекты экзогенного 3,5,3’,5’-тетрайодтиронина позволяют предположить, что в клетках высших растений данное соединение принимает участие в регуляции активности генов подобно тому, как это имеет место в клетках животных.

The phytoremediation of soil contaminated with petroleum depends on the association of plants with rhizosphere bacteria capable of promoting plant growth and destroying petroleum hydrocarbonates. In the present work, we studied the effects of “Lenoil” biological product containing bacteria Pseudomonas turukhanskensis IB 1.1, capable of destroying petroleum hydrocarbons on Secale cereale L plants, which previously proved to be resistant to the weak oil pollution of gray forest soil and to the composition of microorganisms in their rhizosphere. The composition of microorganisms in the rhizosphere of rye roots was studied, morphometric parameters of shoots and roots of rye plants were estimated, and hormone concentration was immunoassayed under conditions of 4% petroleum pollution of the soil. Addition of petroleum to the soil increased the content of oligonitrophilic (by 24%) and hydrocarbon-oxidizing (by 33%) microorganisms; however, the content of cellulolytic (by 12.5 times) microorganisms in the rhizosphere decreased. The use of Lenoil led to a further increase in the number of cellulolytic (by 5.6 times) and hydrocarbon-oxidizing (by 3.8 times) microorganisms and a decrease in the number of oligonitrophilic (by 22.7%) microorganisms in the rhizosphere. Under petroleum pollution, the content of auxins (IAA), zeatin riboside, zeatin nucleotide, and zeatin decreased, while the content of abscisic acid (ABA) increased in the shoots of rye plants. Lenoil treatment led to an eight-fold increase in the IAA content in the roots and a decrease in the ABA content in the aerial part and in the roots. It was shown for the first time that the treatment of petroleum-contaminated soil with “Lenoil” increased root mass due to the development of lateral roots, concurrent with high root IAA content. Petroleum pollution increased the deposition of lignin and suberin in the roots, which strengthened the apoplastic barrier and, thus, reduced the infiltration of toxic components. The deposition of suberin and lignin decreased under ”Lenoil” treatment, indicating a decrease in the concentration of toxic petroleum components in the soil degraded by the bacteria. Thus, the biological preparation reduced the growth-inhibiting effect of petroleum on rye plants by increasing the content of growth-stimulating phytohormones (IAA and cytokinins) and reducing the content of ABA, justifying the importance of further study of relevant hormones for the improvement of phytoremediation.