Effects of exogenous glycinebetaine on cadmium-induced changes in photosynthetic performance, antioxidative metabolism and ATPase in cucumber seedlings

A hydroponic experiment was carried out to study the ameliorative effects of exogenous glycinebetaine (GB) upon cadmium (Cd) toxicity in cucumber seedlings. The results indicated that 50 μmol/L Cd stress decreased soil plant analysis development (SPAD) value, plant height, root length, seedling biomass, activities of ascorbate peroxidase (APX) and ATPase in leaves, stems and roots; however, increased peroxidase (POD) and superoxide dismutase (SOD) activities in all tissues, catalase (CAT) activities in stems/roots. Moreover, Cd stress also elevated leaf/root malondialdehyde (MDA), proline, phenols and flavonoid content in all cucumber tissues over the control. The supplementation of GB (Cd + GB) prominently alleviated Cd-induced growth inhibition and oxidative stress, increased SPAD value and stem ATPase, and improved photosynthetic performance compared with Cd treatment alone. Furthermore, external GB diminished leaf/root MDA accumulation and decreased leaf/root proline contents as well as phenols and flavonoid contents in all tissues. Meanwhile, exogenous GB counteracted Cd-induced alterations of certain antioxidant enzymes. For example, it brought all tissue POD and SOD activities and stem/root CAT activities down towards the control level and significantly increased APX activities, especially in leaves and stems. These data suggested the principal protective mechanism for the exogenous GB against Cd toxicity in cucumber seedlings is closely related to improved photosynthesis, diminished Cd-induced proline and MDA accumulation, enhanced ATPase as well as modulation of antioxidant enzymes.