Antioxidative protection and proteolytic activity in tolerant and sensitive wheat (<Emphasis Type="Italic">Triticum aestivum</Emphasis> L.) varieties subjected to long-term field drought

Field drought studies were performed in order to assess oxidative stress, proteolytic activity and yield loss under natural stress conditions. Flag leaves of two drought-tolerant (Yantar and Zlatitsa) and two drought-sensitive (Miziya and Dobrudjanka) winter wheat varieties were analyzed. Stress intensity was assessed by relative electrolyte leakage and proline accumulation. Senescence progression was followed by loss of chlorophyll and protein. Lipid peroxidation, H₂O₂ content, activities of superoxide dismutase (SOD), catalase (CAT), and non-specific peroxidase (GPX) isoforms, as well as proteolytic activities were analyzed from heading throughout grain filling. Weakening of membrane integrity and oxidative damage to lipids were more pronounced in the sensitive varieties under field drought. The activities of Fe- and Cu/Zn SOD isoforms decreased in the controls, but remained high in drought-treated plants. The activities of MnSOD isoforms and CAT were enhanced towards grain filling, especially in the sensitive varieties under drought. GPX activities were rised under drought but progressively diminished. Accelerated senescence under field drought was linked to higher proteolytic activity with variety specific differences in the protease response, but without a clear correlation to drought resistance or sensitivity. Field drought led to higher oxidative stress more pronounced for drought sensitive varieties, especially during the grain filling period.