A hydroponic study was conducted to determine the effects of selenium (Se: 0, 3, 6 μmol L−1) on senescence-related oxidative stress in garlic plants grown under two sulfur (S) levels. We evaluated the yields of plants harvested at 160 and 200 days after sowing. Plants grown under a low Se dose (0.3 μmol L−1) at low S level showed higher yields (12.0% increase in fresh weight yield, 13.7% increase in dry weight yield) than the controls, despite a decrease in chlorophyll concentration. Compared with control plants, the Se-treated plants showed lower levels of lipid peroxidation. The Se-treated plants also showed higher activities of glutathione peroxidase and catalase, but lower superoxide dismutase activities. Changes in Fv/Fm values and proline contents were affected more strongly by S than by Se. On the basis of our results, we can conclude that Se plays a key role in the antioxidant systems in garlic seedlings. It delays senescence by alleviating the peroxide stress, but it can be toxic at high levels. A high S level may increase tolerance to high Se concentrations through reducing Se accumulation in plants.

A greenhouse experiment was carried out to determine plant growth, reactive oxygen species (ROS) metabolism in roots and functions of plasma membrane (PM) and tonoplast in cucumber seedlings (Cucumis sativus L. cv. Xintaimici) treated with 40 μmol L-1 CuSO4·5H2O, which were either ungrafted or grafted onto the rootstock (Cucurbita ficifolia). Cu treatment inhibited growth, induced significant accumulation of H2O2 and led to serious lipid peroxidation in cucumber roots, and the ROS-scavenging enzymes activities in grafted seedlings roots were significantly higher than that of ungrafted plants, thus less accumulation in grafted cucumber roots induced by Cu. As a result, lipid peroxidation in roots decreased. Furthermore, the activities of H+-ATPase, H+-PPase and Ca2+-ATPase in PM and/or tonoplast in grafted cucumber seedlings under Cu stress were obviously higher than that in ungrafted plants, resulting into higher ability in grafted plants to expulse the excess H+, promote the cytoplasm alkalinization, regulate the intracellular Ca2+ concentration and brought the cytoplasma concentration of free Ca2+ to extremely low level under Cu stress.