Mechanisms formation of systemic acquired resistance in spring barley plants (<i>Hordeum vulgare</i> L.) during infection by the pathway of dark brown spot

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The physiological and biochemical responses in spring barley plants to infection with a hemibiotrophic phytopathogenic fungus B. sorokiniana was studied. It was found that these responses of the plant organism are regulated by signaling pathways with the participation of the salicylic acid mediator (SA) and are associated with oxidative stress-localized accumulation of reactive oxygen molecules (ROS) in infected cells and/or neighboring cells. The activation of the microsomal fraction of NADPH oxidase isolated from barley leaves on days 1 and 3 after fungal infection was revealed, which is known to be responsible for the rapid formation of ROS in plant cells under the influence of fungal infection. At the same time, an increase in the activity of the peroxidase enzyme detoxifying ROS, in particular Н 2 О 2 , was observed in relation to the control (uninfected plants) by 1.6 and 2.2 times on the 1st and 3rd day after exposure, respectively. The inclusion of antioxidant defense mechanisms led to the stabilization of lipid peroxidation processes several days after infection. A reliable increase in the total content of water-soluble phenolic substances in the infected plant tissues was shown to have a protective effect on plants under stress, as well as an increase in the free pool of endogenous SA by 9 and 30 % during the first 24 hours and the next 3 days after infection, respectively. The data obtained indicate that endogenous S А is involved in the responses to infection of B. sorokiniana barley seedlings and is a necessary factor for the activation of SAR (systemic acquired resistance), which manifests itself in the accumulation of free S А and a decrease in its conjugated form in response to infection.