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.

Abstract:In forest research and nursery practice there is often a need to monitor the condition and responses of trees to different stressors. Chlorophyll content in leaf is a good indicator of plant health and can be measured rapidly in many repetitions using the chlorophyll meter SPAD-502Plus. This practical tool provides the values of chlorophyll content in relative units (SPAD values), therefore it should be calibrated for each species to determine chlorophyll content in physiological units. In this study, the chlorophyll meter SPAD-502Plus was calibrated to be used for total chlorophyll (Chl), chlorophyll a (Chl a), chlorophyll b (Chl b) and carotenoids (Car) contents determination in leaves of Quercus petraea and Prunus serotina seedlings growing in different light environments. In the same leaf, SPAD values were measured with the Chl meter, and then photosynthetic pigments content (PP; chlorophyll and carotenoids) was consistently assessed using a conventional extraction method. The measurements were conducted once a month from May to November in three light treatments to obtain the widest possible range of the PP content values. To estimate total Chl content in leaves using the chlorophyll meter the quadratic polynomial functions: y = 0.0374x 2 + 0.5345x + 0.5137 and y = 0.024x 2 + 2.1998x -32.7866 were obtained from the relationship between the Chl meter SPAD readings and total Chl determined spectrophotometrically for P. serotina and Q. petraea, respectively. Chl was higher under shade compared with full light regime and Car were linearly correlated with Chl. PP content was positively correlated with air temperature except for Car in P. serotina leaves. It was concluded that at the same soil conditions chlorophyll content in leaves of Q. petraea and P. serotina depended on species, light regimes and temperature of growth. The chlorophyll meter can be used as a practical tool to monitor and compare photosynthetic pigments content in leaves between tree species or populations acclimated to different environments together with a control of abiotic and biotic factors affecting pigments content and leaf optical properties.

The effect of soil drought on leaf water content, proline content, and the activity of guaiacol (GuPX) and ascorbate (APX) peroxidases as well as the level of lipid peroxidation were investigated in leaves of drought resistant red fescue (Festuca rubra) and drought sensitive perennial ryegrass (Lolium perenne). Plants were grown under glasshouse conditions in soil pot culture. 26 day-old grasses were exposed to drought by withholding irrigation for 18 days. Water content in leaves of perennial ryegrass decreased more than in red fescue throughout the experimental period. On the other hand, proline content (PC) was higher in red fescue. The activity of APX and GuPX increased in leaves of red fescue, while it did not change in perennial ryegrass. Our data demonstrate that both red fescue and perennial ryegrass were able to survive applied drought, as shown by a lack of stress-induced lipid peroxidation and hence no evidence of oxidative damage. We speculate, that the observed drought stress tolerance at cellular level was associated with the ability to accumulate proline, and to maintain high activity of APX and GuPX, resulting in protection against oxidative damage and lipid peroxidation. It seems that this mechanism works better in red fescue.