EFFECTS OF MODERATE DROUGHT ON ASCORBATE PEROXIDASE AND GLUTATHIONE-REDUCTASE ACTIVITIES IN MESOPHYLL AND BUNDLE-SHEATH CELLS OF MAIZE

Mesophyll and bundle sheath cells of maize leaves (Zea mays L,) both c ontain the enzymes ascorbate peroxidase (AP: EC 1.11.1.11) and glutath ione reductase (GR; EC 1.6.4.2) which are involved in hydrogen peroxid e detoxification. Since bundle sheath cells of maize are deficient in photosystem II and have high CO2 levels, oxidative stress may be less severe in these cells than in mesophyll cells. The present study was c onducted to determine if AP and GR activity levels preferentially incr ease in mesophyll cells relative to bundle sheath cells when plants ar e subjected to moderate drought. Although drought inhibited the growth of greenhouse-grown plants, it did not affect the levels of protein. chlorophyll or AP. GR was unaffected by drought in whole leaf tissue a nd mesophyll cells, but did increase slightly in bundle sheath cells. This slight increase is of questionable biological importance. AP and GR activity levels were similar in mesophyll cells, bundle sheath cell s and in whole leaf tissue. The data suggest that moderate drought has little effect on enzymes of the hydrogen peroxide scavenging system a nd that mesophyll and bundle sheath cells may be exposed to similar le vels of hydrogen peroxide.