Role of Endogenous Salicylic Acid as a Hormonal Intermediate in the Bacterial Endophyte Bacillus subtilis-Induced Protection of Wheat Genotypes Contrasting in Drought Susceptibility under Dehydration

Abstract

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.

Proline Spray Relieves the Adverse Effects of Drought on Wheat Flag Leaf Function

“…In our study, the content of MDA in the flag leaves of wheat was elevated under drought stress, as MDA content typically increases in plants experiencing stressful conditions and it is an indicator of membrane impairment [42]. Another intriguing observation in this study is that exogenous proline further increased the MDA content in the flag leaves of wheat.…”

Succession of tissue microbial community during oat developmental

“…MDA can be used to understand the degree of membrane lipid peroxidation, which indirectly measures the degree of membrane system damage and plant stress resistance. MDA can effectively protect wheat seedlings from drought damage [ 25 ]. Almost all aerobic bacteria rely on enzyme-promoted and non-enzyme-promoted antioxidants to combat the presence of reactive oxygen species.…”

Endophytic Plant Growth-Promoting Bacterium Bacillus subtilis Reduces the Toxic Effect of Cadmium on Wheat Plants

“…Previously, we found that the pre-sowing seed treatment with the PGPM B. subtilis strain 10-4 had a growth-stimulating and anti-stress effect on various plants, including wheat under the influence of salinity [44,45], drought [46], and a combination of herbicide and drought [47]. It was shown that the protective effect of strain 10-4 is based on its ability to colonize the internal tissues of the host plant (including wheat), produce auxins, fix atmospheric nitrogen, solubilize phosphates, modulate the level of plant phytohormones (in particular, salicylic acid) [48] and the content of photosynthetic pigments, regulate the components of the ascorbate-glutathione complex [49], reduce stress-induced oxidative and osmotic cell damages, and also accelerate the lignification of root cell walls, as demonstrated for bean plants during salinity [50].…”