Activity of photosynthetic membranes in Fusarium oxysporum-infected cucumber (Сucumis sativus L.) plants under different proportions of blue LED illumination

The effect of LED illumination with different proportions of blue light (BL, 20 and 60 %) and different durations on the functionality of photosystems (PS) in healthy and infected with the fungus Fusarium oxysporum (Fus. oxy.) cucumber leaves was studied. Long-term exposure (25 days) to a light regime with a high share of BL, 60 % and subsequent infection with Fus. oxy., suppressed the functional activity of PSII relative to white light (WL), which was reflected in a significant decrease in the maximum fluorescence of temporarily closed PSII reaction centers (F m ), the effective quantum yield of photochemical reactions (F v /F m ), the maximum quantum efficiency of PSII (Y(II)), as well as in changes to the nature of the redistribution of absorbed light energy. This resulted in a decline in the intensity of photochemical conversion (qP), the number of open PSII reaction centers (qL) and the rate of electron transport through PSII (ETR(II)). During a 7-day exposure of plants to different light conditions, the main changes in PSII parameters were observed only in infected leaves formed in the BL, 60 %. Growing on WL and BL, 20 % only slightly changed the contribution of the electron flow on the donor and acceptor sides of PSI in infected cucumber leaves, without affecting the level of P700 oxidation and the quantum yield of photochemical reactions. Infection of plants grown for a long time on BL, 60 % caused a 10-fold decrease in the quantum yield of photochemical reactions of PSI and a significant increase in non-photochemical energy dissipation on the donor and acceptor sides of PSI. The stress effect of the pathogen also enhanced the suppressive effect of BL, 60 % at short exposure, which was reflected in a significant decrease of such parameters as the quantum yield of PSI (Y(I)) and the efficiency of electron transfer in the electron transport chain of PSI (ETR(I)). The results obtained can be used as a methodological basis for the development of energy-saving LED light sources optimized for growing cucumber plants in closed soil, as well as for monitoring the degree of infection of plants in the early stages of Fusarium infection.