Proline and Betaine Upregulated Glutathione Dependent Detoxification Enzymes in Tolerant Maize Seedlings under Saline Stress

Glutathione S-transferases (GSTs, EC: 2.5.1.18) and Glyoxalases [Glyoxalase-I (Gly-I, EC: 4.4.1.5) and glyoxalase-II (Gly-II, EC: 3.1.2.6)] are major glutathione dependent detoxification as well as important antioxidants enzymes in plants. On the other hand, proline and betaine are important osmoprotectants in plants under abiotic stresses including salinity. In this study, roles of GST, Gly-I, Gly-II and glutathione were investigated on cytotoxic metabolites in presence of 15 mM proline and betaine under 16 dSm -1 salinity in leaves of seedlings of a saline tolerant maize inbred CZ-10 to understand the underlying saline tolerant mechanism. The salinity stress increased the contents of H 2 O 2 , melondialdehyde (MDA), methylglyoxal (MG) along with decreased reduced glutathione (GSH) and glutathione redox state over control. The activities of GST and Gly-I increased under saline stress. However, activity of Gly-II decreased with stress duration. The application of proline and betaine in saline water reduced the contents of H 2 O 2 , MDA and MG. Conversely, proline and betaine increased the activities of GST, Gly-I and Gly-II, and GSH and glutathione-redox state over salinity stress. The western blotting of the soluble protein also suggested the accumulation of maize GST in leaf under salinity stress. The accumulation of GST along with reduced contents of H 2 O 2 and MDA suggested its detoxification roles on organic hydroperoxides under saline stress. The higher activities of Gly-I and Gly-II concurrently with lower content of MG indicated their protective roles from cytotoxic MG. Considering all, this study concluded that both proline and betaine provided protective roles in maize seedlings under salinity stress by maintaining GSH and its related detoxification enzymes.