AtNDB2 Influences the Production of Reactive Oxygen Species and the State of Photosystem II under Cold Stress

Low-temperature stress, which reduces the productivity of cultivated plants and their cultivation potential in temperate climate zones, is accompanied by oxidative stress. The reduction of ROS generation in plant cells can be achieved, among other methods, by activating alternative electron transport pathways in mitochondria. The aim of the study was to assess the influence of the heterologous AtNDB2 (mitochondrial external alternative NADH dehydrogenase from Arabidopsis thaliana L. Heynh.) gene expression on the functional state of the photosynthetic apparatus, the level of ROS generation, the expression of genes encoding enzymes that form the mitochondrial alternative electron transport pathway, and the superoxide dismutase (SOD) activity under low positive temperature stress in tobacco plants (Nicotiana tabacum L.). It was shown that in the leaves of transgenic plants (13S line) under low-temperature stress, the decrease in the maximum quantum yield of PSII was less than in wild type (WT) plants. Also higher value of the non-photochemical quenching of chlorophyll fluorescence (NPQ) in the leaves of 13S line was detected. A decrease in the ROS production in the leaves of 13S plants under low-temperature stress was observed. AtNDB2 heterologous expression was accompanied by an increase in the number of mRNA of genes encoding other mitochondrial alternative electron transport pathway components—NDA2 and AOX1a. This fact confirms the possibility of forming this alternative pathway in the mitochondria of 13S plants—NDB2/NDA2–Q/QH2–AOX. Under control conditions, AtNDB2 expression led to a slight Mn-SOD activity increase. Under cold stress, the different SOD isoforms activity in the 13S plant leaves was lower than in WT plants.