Chilling injury induction and water deficiency is accompanied by changes on the photosynthetic apparatus and antioxidant response in primary Tagetes leaves

Plants are often subjected to the changes in temperature in their environment. Chilling stress is a complex phenomenon which reflects various changes in their function and structure. The destructive effect of chilling temperatures is visible not only in disturbances of physiological metabolic processes, but also in generating reactive oxygen species (H2O2, O2 - , OH). These conditions of chilling stress (like other kind of stresses) results to an increase of active oxygen species (AOS) such as hydrogen peroxide. Water deficits is one of the common environmental factor limiting crop productivity. It brings about changes in membranes properties and produce O * 2 and other reactive oxygen species. It is now becoming clear that oxidants are important in signal transduction processes. The high level of ROS in the cells of the plants is the reason of the occurrence of oxidative stress conditions there. The antioxidative system that includes low-molecular antioxidants (glutathione, ascorbate, cysteine) and antioxidative enzymes (superoxide dismutase-SOD, catalase-CAT, peroxidase- POX) is the mechanism protecting ROS. In the conducted research, we have demonstrate that H2O2 and peroxidase activity increased in leaves and especially when the plants were treated with low temperature and water deficit simultaneously. In this study also the changes in the levels of some stress markers (products of lipid peroxidation, of malondialdehyde equivalents, (MDA), hydrogen peroxide) and activities of stress defence enzymes (catalase, peroxidase, superoxide dismutase). The plants were grown under laboratory controlled conditions (growth chamber) as soil culture in plastic pots (30x30x10 cm). In the stress conditions the chlorophyll, protein contents significantly declined. Our results indicate specific responses of the antioxidant enzymes under stress conditions and a possible synergetic action of water stress and chilling causing intense changes in membrane properties, compared to samples exposed to either of the stresses individually. We concluded that it is the concerned action of antioxidants, and not an antioxidant alone, which confers protection from oxidative stress in chloroplasts of chilling stressed plants.