Localization of reactive oxygen species and change of antioxidant capacities in mesophyll and bundle sheath chloroplasts of maize under salinity

Abstract

In maize, the structure of bundle sheath cell (BSC) chloroplasts is less subject to salinity stress than that of mesophyll cell (MC) chloroplasts. To elucidate the difference in sensitivity to salinity, antioxidant capacities and localization of reactive oxygen species were investigated in both chloroplasts. Transmission electron microscopic observation showed that O2 (-) localization was found in both chloroplasts under salinity, but the accumulation was much greater in MC chloroplasts. H2 O2 localization was observed only in MC chloroplasts of salt-treated plants. In isolated chloroplasts, the activities of superoxide dismutase (SOD, EC 1.15.1.1), ascorbate peroxidase (APX, EC 1.11.1.11) and dehydroascorbate reductase (DHAR, EC 1.8.5.1) were increased by salinity. While the enhancement of SOD activity was similar in both chloroplasts, the increase of APX and DHAR activities were more pronounced in BSC chloroplasts than in MC chloroplasts. Monodehydroascorbate reductase (MDHAR, EC 1.6.5.4) and glutathione reductase (GR, EC 1.6.4.2) were undetectable in BSC chloroplasts, while they increased in MC chloroplasts under salinity. Although ascorbate content increased by salinity only in BSC chloroplasts, glutathione content increased significantly in both chloroplasts, and was higher in MC chloroplasts than in BSC chloroplasts. The content of thiobarbituric acid-reactive substances, which is an indicator of lipid peroxidation, was significantly increased by salinity in both chloroplasts. These results suggested O2 (-) -scavenging capacity was comparable between both chloroplasts, whereas H2 O2 -scavenging capacity was lower in MC chloroplasts than in BSC chloroplasts. Moreover, the increased lipid peroxidation under salinity was associated with the structural alteration in MC chloroplasts, while it had less impact on the structure of BSC chloroplasts.

Salinity induces membrane structure and lipid changes in maize mesophyll and bundle sheath chloroplasts

“…Maize BSC chloroplasts are characterized by extremely rudimentary grana (Hasan et al , ), and therefore exhibit little oxygen evolution and produce low levels of reducing equivalents (Hatch and Osmond ). Consistent with the idea that BSC chloroplasts are less affected by ROS than are MC chloroplasts, ROS accumulation is significantly lower in BSC chloroplasts than in MC chloroplasts (Omoto et al ). Furthermore, BSC chloroplasts possess considerably higher activities of antioxidant enzymes than do MC chloroplasts under salt‐treated conditions (Omoto et al ).…”

“…Consistent with the idea that BSC chloroplasts are less affected by ROS than are MC chloroplasts, ROS accumulation is significantly lower in BSC chloroplasts than in MC chloroplasts (Omoto et al ). Furthermore, BSC chloroplasts possess considerably higher activities of antioxidant enzymes than do MC chloroplasts under salt‐treated conditions (Omoto et al ). The membranes of BSC chloroplasts tend to be resistant to salinity stress not just in maize but in all C 4 plant species examined (Omoto et al , ).…”

“…Two main techniques are used to separate MC and BSC chloroplasts, namely mechanical and enzymatic methods (Romanowska et al ). In this study, we applied the enzymatic method, because the mechanical method apparently causes cross‐contamination of BSC chloroplasts in the preparations of MC chloroplasts (Omoto et al ). While the enzymatic method can separate highly purified MC and BSC chloroplasts, this method occasionally leads to hydrolysis of specific membrane lipids according to the experimental conditions and materials (Webb and Williams , Browse et al ).…”

“…While the enzymatic method can separate highly purified MC and BSC chloroplasts, this method occasionally leads to hydrolysis of specific membrane lipids according to the experimental conditions and materials (Webb and Williams , Browse et al ). Therefore, we compared the glycerolipid contents of BSC chloroplasts isolated by the enzymatic and mechanical methods (Kanai and Edwards , Omoto et al ). In BSC chloroplasts of maize control plants, we found that MGDG contents appeared to be slightly higher with mechanical isolation, whereas DGDG and SQDG contents were lower with mechanical isolation than with enzymatic isolation [Figs and S1 (Supporting Information)].…”

Reactive oxygen species: Reactions and detection from photosynthetic tissues

“…O 2 • has been detected with NBT from legume roots [299], pea leaves [300], diatoms [301] and from extracted leaf material of maize [302]. To quantify the signal, the biological material has to be made transparent by removing Chl [299] or centrifuged away [302], but the precipitated product of the NBT-O 2 • reaction can be histochemically localized. A method for quantification of O 2 • from stained leaves has been developed [303].…”