Differential sensitivity of C3 and C4 plants to water deficit stress: Association with oxidative stress and antioxidants

The metabolic reasons associated with differential sensitivity of C3 and C4 plant species to water stress are not well understood. In the present study, 15-day-old wheat (Triticum aestivum) and maize (Zea mays) plants, representatives of C3 and C4 plants, respectively, were subjected to mild (-0.4 MPa), moderate (-0.8 MPa) and high (-1.5 MPa) water stress levels induced by PEG-6000 for 7 days under controlled conditions. The roots and leaves of these plant species were evaluated for oxidative damage and antioxidants along with stress injury (as electrolyte leakage), water content and abscisic acid. While at mild stress, both the plant species did not vary significantly from each other for stress injury, moderate and high stress levels caused considerably more damage to wheat as compared to maize. This was accompanied by more loss of water and chlorophyll by wheat relative to maize at these stress levels. ABA content remained unaffected at mild stress level in both the plant species but showed significantly higher content in roots and leaves of maize than wheat at moderate and high stress levels. The oxidative damage in terms of malondialdehyde and H2O2 content was markedly higher in wheat as compared to maize at moderate and high stress levels. Relatively, maize had significantly higher content of non-enzymatic (ascorbic acid and glutathione) and enzymatic antioxidants (ascorbate peroxidase, dehydroascorbate reductase and glutathione reductase, especially in its leaves). In contrast, wheat possessed more activity of catalase in its roots as well as leaves in comparison to maize. Superoxide dismutase activity showed little variation between the two plant species. Leaves of both the species experienced more damage than roots. These findings suggested that differential sensitivity of C3 and C4 plants to water stress appear to be partially governed by their ability to counter oxidative stress, pertinently involving ascorbic acid and glutathione.