The ability of brassinosteroids, such as 24-epibrassinolide (EBL) to increase the resistance of oilseed rape plants (Brassica napus L.) to salt stress (175 mM NaCl) was investigated along with the possible mechanisms of their protective action. Seedlings were grown for three weeks on the Hoagland-Snyder medium under controlled conditions. The experimental plants were treated with either (1) 175 mM NaCl, or (2) 10⁻¹⁰ M EBL, or (3) 175 mM NaCl plus 10⁻¹⁰ M EBL by adding the corresponding components to the growth medium. The exposure was 7 and 14 days. As compared to the control, salinization inhibited plant height by 33–35%, reduced leaf area by 2.0–2.5 times, reduced 2.5- and 2-fold plant fresh and dry weight, respectively, reduced water content of plant tissues by 26–31% and, twofold, the content of chlorophylls a and b. Plants responded to NaCl by developing oxidative stress conditions, lowering the osmotic potential of the cell contents down to −2 MPa, accumulating proline (by 43–52 times) and low-molecular-weight phenolics (by 1.9–2.7 times). Oilseed rape plants were shown to respond to salinization with an increase of endogenous content of steroid hormones: 24-epibrassinosteroids (24-epibrassinolide and 24-epicastasterone), 24S-methyl-brassinosteroids (brassinolide and castasterone), and 28-homobrassinosteroids (28-homobrassinolide and 28-homocastasterone); such evidence indirectly confirms the involvement of brassinosteroids in the development of salt tolerance. Adding EBL to the nutrient medium under optimal growth conditions did not significantly affect the indices under study. Under salt stress, EBL showed a pronounced protective effect: stem growth was fully restored, plant assimilation area increased by as much as 67–76% as compared to the control index, fresh and dry weight largely recovered (up to 85–92% of the control values), and the inhibitory effect of NaCl on photosynthetic pigments was diminished. Exogenous EBL impeded the development of NaCl-dependent lipid peroxidation and increased the osmotic potential of the leaf cell contents. The protective effect of EBL under salt stress was probably associated with EBL antioxidant effect, rather than the hormone-induced accumulation of proline and of low-molecula-weight phenolics, as well as with the ability to regulate water status by maintaining intracellular ion homeostasis.

This is the first study to show that brief pretreatment of potato plants with two brassinosteroids differing in structure causes in plants the ability to react to delayed salt stress by accumulation...

Melatonin is among one of the promising agents able to protect agricultural plants from the adverse action of different stressors, including salinity. We aimed to investigate the effects of melatonin priming (0.1, 1.0 and 10 µM) on salt-stressed potato plants (125 mM NaCl), by studying the growth parameters, photochemical activity of photosystem II, water status, ion content and antioxidant system activity. Melatonin as a pleiotropic signaling molecule was found to decrease the negative effect of salt stress on stolon formation, tissue water content and ion status without a significant effect on the expression of Na⁺/H⁺-antiporter genes localized on the vacuolar (NHX1 to NHX3) and plasma membrane (SOS1). Melatonin effectively decreases the accumulation of lipid peroxidation products in potato leaves in the whole range of concentrations studied. A melatonin-induced dose-dependent increase in Fv/Fm together with a decrease in uncontrolled non-photochemical dissipation Y(NO) also indicates decreased oxidative damage. The observed protective ability of melatonin was unlikely due to its influence on antioxidant enzymes, since neither SOD nor peroxidase were activated by melatonin. Melatonin exerted positive effects on the accumulation of water-soluble low-molecular-weight antioxidants, proline and flavonoids, which could aid in decreasing oxidative stress. The most consistent positive effect was observed on the accumulation of carotenoids, which are well-known lipophilic antioxidants playing an important role in the protection of photosynthesis from oxidative damage. Finally, it is possible that melatonin accumulated during pretreatment could exert direct antioxidative effects due to the ROS scavenging activity of melatonin molecules.

The considerable decrease in crop productivity associated with the expansion of saline soils is an acute problem in agriculture. Endophytic fungi positively affect plant fitness under salinity conditions. The effects of potato inoculation with the conidia of the Beauveria bassiana strain Sar-31 on growth (the weight of fresh and dry biomass, shoot and root length, numbers of stolons and leaves, and the leaf surface) and physiological indices (the concentration of pigments, free proline and malondialdehyde, and antioxidant enzymes’ activity) were evaluated under moderate chloride salinity (100 mM). The results indicated that the plant’s association with the fungus mitigated the negative impact of salinity probably because of the activation of antioxidant enzymes and accumulation of free proline in potato tissues. Moreover, under the influence of B. bassiana Sar-31, the number of stolons significantly increased, which is one of the main characteristics of potato as an agricultural crop. Thus, Sar-31 may be a promising candidate for further investigation of its ability to stimulate growth and increase the stress tolerance of potato plants.

Endophytic entomopathogenic fungi are promising agents for the promotion of plant growth, the activation of immunity, and protection against phytopathogens. However, physiological changes in plants after treatment with fungi are insufficiently studied. We investigated the effect of potato inoculation with conidia from Metarhizium robertsii and Beauveria bassiana on the growth (fresh and dry weight, length of shoots and roots, counts of stolons and leaves, and total surface area of leaves) and physiological parameters (pigment contents, free proline and malondialdehyde content, and activity of antioxidant enzymes) at the initial stage of the plant–fungus interaction (seven days) under hydroponic conditions. The results showed that the fungi could act as an immune-modulating factor for plants based on the increase in malondialdehyde and proline contents. At the same time, we observed growth retardation and a decrease in the content of photosynthetic pigments, which may be caused by a tradeoff between plant growth and the immune response.