Oxidative stress is a state of impaired balance between the formation of free radicals and antioxidant capacity of the body. It causes many defects of the body, e.g. lipid peroxidation, DNA and protein damage. In order to prevent the effects of oxidative stress, the organism has developed defence mechanisms. These mechanisms capture and inhibit the formation of free radicals and also chelate ion metals that catalyse free radical reactions. Trace elements are components of antioxidant enzymes involved in antioxidant mechanisms. Selenium, as a selenocysteine, is a component of the active site of glutathione peroxidase (GPx). The main function of GPx is neutralization of hydrogen peroxide (H2O2) and organic peroxide (LOOH). Furthermore, selenium is a structural part of a large group of selenoproteins that are necessary for proper functioning of the body. Manganese, copper and zinc are a part of the group of superoxide dismutase enzymes (MnSOD, Cu/ZnSOD), which catalyse the superoxide anion dismutation into hydrogen peroxide and oxygen. Formed hydrogen peroxide is decomposed into water and oxygen by catalase or glutathione peroxidase. An integral component of catalase (CAT) is iron ions. The concentration of these trace elements has a significant influence on the activity of antioxidant enzymes, and thus on defence against oxidative stress. Even a small change in the level of trace elements in the tissue causes a disturbance in their metabolism, leading to the occurrence of many diseases.

No abstract

In order to determine the concentration ranges of IAA and kinetin required for callus induction and subsequent callus growth, stem pieces and floral buds from plants of four various sex types of <i>Cucumis sativus</i> L. were grown in the <i>in vitro</i> culture. Requirements for phytohormones depend upon the kind of organ and the sex line. Tissues of male and monoecious lines were more sensitive to IAA deficiency, whereas male and hermaphrodite ones to kinetin deficiency. This tendency has been observed to occur for nearly 18 months.

Article was published originally without  abstract.