The aim of the study was to evaluate the antioxidant activity of selenium in the roots of Cucumis sativus L. seedlings pre-treated with selenium (Se) in the form of sodium selenite at concentrations of 1, 5, and 10 µM, and then subjected to a water deficit (WD). It has been hypothesized that Se, in low concentrations, alleviates an oxidative stress caused by a WD in the cucumber roots. A WD was introduced by the surface dehydration of roots. The aim of the research was to compare the changes accompanying oxidative stress in plants growing in the presence of Se and in its absence. The study concerns the generation of reactive oxygen species (ROS) —superoxide anions (O2•−), hydrogen peroxide (H2O2), and hydroxyl radicals (•OH)—as well the activities of the antioxidant enzymes lowering the ROS level—ascorbate peroxidase (APX), peroxidase (POX), catalase (CAT), and superoxide dismutase (SOD). A WD caused oxidative stress, i.e., the enhanced generation of ROS. Selenium at the concentrations of 1 and 5 μM increased the tolerance of cucumber seedlings to oxidative stress caused by a WD by increasing the activities of the antioxidant enzymes, and it also limited the damage of plasma membranes as a result of the inhibition of lipid peroxidation.

Seven-day-old seedlings of cucumber (Cucumis sativus L.) cv. Wisconsin were treated with 0.

Rye seedlings, tillering plants and crop residues were allowed to decompose in model incubation experiments. Young tissues gave rise to high concentrations of allelochemicals, whereas crop residues did not produce inhibitors. Seven phenolic acids were identified in the investigated materials; p-hydroxybenzoic, protocatechuic, gallic, vanillic, syringic, p-coumaric, ferulic as well as benzoic acid. However, neither the level of these acids nor the total content of phenolic compounds corresponded to the level of phytotoxicity determined in bioassays. This demonstrated that, apart from phenolics, other unidentified water-soluble organic compounds were also responsible for the toxicity of rye decomposition products.

Seven-day-old seedlings of cucumber (Cucumis sativus L.) cv. Wisconsin were treated with 0.01, 0.1 and 0.5 mM solutions of derivatives of cinnamic acid (ferulic and p-coumaric acids) and benzoic acid (p-hydroxybenzoic and vanillic acids) as stress factors. In cucumber roots phenolics (free and ghicosylated), phenol 13-ghicosyltransferase (E.C. 2.4.1.35) activity as well as membrane permeability were examined. The most intensive ghicosylation took place in the first hour of stress duration in roots treated with 0.01 mM ferulic and p-coumaric acids and with 0.01 and 0.1 mM p-hydroxybenzoic and vanillic acids. At these concentrations a high phenol 13-glucosyltransferase activity was found. The deterioration of capacity for phenolic glucosylation as well as the decrease of the phenol 13-glucosyltransferase was observed at the higher concentrations. It was associated with increased membrane permeability.

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