Efekti vodnog deficita i suficita na antioksidativni sistem zaštite kod dva hibrida kukuruza (Zea mays L.)

Plants are continuously challenged by the rising incidence of drought and flooding as a consequence of global warming. These stresses may cause severe depression in the plant’s growth by inhibiting photosynthesis, inducing oxidative cell damage, and cell respiration changes. The present work aimed to study the effect of flooding and drought stress on physiological, oxidative, and antioxidative parameters in leaves of two maize hybrids (ZP 555 and ZP 606). Maize plants` leaves at the stage of three fully developed leaves were harvested after 6, 24, 72, and 144 hours of applied flooding stress and after 8 and 15 days after applied drought stress. Leaves from experimental plants and control plants were used for the determination of physiological (relative water content (RWC), the content of photosynthetic pigments and soluble proteins, proline), oxidative stress parameters (the content of malondialdehyde (MDA) and H2O2), as well as antioxidants (the total polyphenols content (Phe), and activity of antioxidative enzymes [catalase (CAT, EC 1.11.1.6), superoxide dismutase (SOD, EC 1.15.1.1), ascorbate peroxidases (APX, EC 1.11.1.11), and Class III peroxidases (POX, EC 1.11.1.7)]). Results indicated that drought and flooding stress-induced time-dependent changes of measured parameters and those hybrids differ in stress response. Changes in photosynthesis can be seen thought modifications in photosynthetic pigments concentration. An increase in the concentration of chlorophylls and carotenoids have been noted during flooding in ZP 555 hybrids. On the other hand, flooding stress decreased the chlorophyll b and carotenoid concentrations in ZP 606 hybrids. A decrease in the concentration of chlorophyll a and carotenoids and an increase in chlorophyll b concentration were a response of both examined hybrids on drought stress. Also, intensive protein synthesis was noted in both hybrids during flooding. More intensive oxidative stress levels were correlated with an increase in H2O2 in hybrid ZP 555. Induced SOD and POX activities and concentration of polyphenols were detected in both hybrids during flooding stress. Polyphenols/POX system provided faster hydrogen peroxide displacement cells of ZP 606 hybrids. On the other hand, a decline in the concentration of soluble proteins and proline was drought-stress induced. The drought-induced decrease in proline concentration caused a disbalance in cell osmotic potential. The sensitivity of the tested hybrids to water deficit was noted during the prolongation of this stress, which caused an increase in the hydrogen peroxide concentration (in hybrids ZP 555) and lipid peroxidation (in both hybrids). Moreover, a drought-induced increase in the activity of antioxidative enzymes, SOD (both hybrids), CAT and POX (only ZP 555) was noted. A decline in the concentration of polyphenols caused by drought stress makes both hybrids drought sensitive. The decrease in the concentration of MDA and H2O2, followed by an increase in activity in antioxidative enzymes and concentration of nonenzymic, together with an increase in osmoprotectants accumulation, presents valuable tools for the selection of flooding/drought-tolerant plants. The present study results suggest that a more robust antioxidative metabolism is essential under flooding stress and could be a protective strategy against oxidative damage induced by flooding in ZP 606 maize plants compared to ZP 555 plants. On the other hand, enlarge in the concentration of MDA, followed by a decrease in protein, proline and polyphenols concentration, suggests that both tested 30 days old hybrids are defenceless against oxidative damage induced by 15-days drought stress.