-1 Localization of antioxidant enzymes in the cellular compartments of sorghum leaves Durai Sundar * , B. Perianayaguy and A. Ramachandra Reddy * School of Life Sciences, Pondicherry University, Pondicherry – 605 014, India; *Authors for correspondence (e-mail: d_sundar@yahoo.com, arreddy@yahoo.com; phone: +91-413-2655991; fax: +91-413-2655211/ 2655265) Received 27 April 2004; accepted in revised form 30 September 2004 Key words: Antioxidant enzymes, Bundle sheath, Mesophyll, Sorghum vulgare Abstract The localization of antioxidant enzymes between the mesophyll and bundle sheath cells were determined in sorghum (Sorghum vulgare L.) leaves. The activity of antioxidant enzymes like superoxide dismutase (SOD), catalase (CAT), guaiacol peroxidase (POD), ascorbate peroxidase (APX) and glutathione reductase (GR) were assayed in whole leaf, mesophyll and bundle sheath fractions of sorghum leaves subjected to water-limited conditions. Drought was imposed by withholding water and the plants were maintained at different water potentials ranging from 0.5–2.0 MPa. The purity of the isolates was tested using the marker enzymes like RuBPcase and PEPcase. GR was mostly localized in mesophyll fraction, while SOD, APX and peroxidase were located in bundle sheath cells. Catalase was found to be equally distributed between the two cell types. Under water stress conditions, most of the SOD activity was found in the bundle sheath tissues. Little or no activity of the enzymes CAT, APX or POD was found in the mesophyll extracts when exposed to water stress. GR activity increased when exposed to low water regimes. From this study, it is clear that antioxidants are differentially distributed between the mesophyll and bundle sheath cells in sorghum leaves. Under water stress conditions, the mesophyll cells showed less damage from oxidative stress when compared to the bundle sheath cells. This is critical for determining the sensitivity of sorghum to extreme climatic conditions. Abbreviations: AOS – active oxygen species; APX – ascorbate peroxidase; BS – bundle sheath cells; CAT – catalase; GR – glutathione reductase; M – mesophyll cells; MDA – monodehydroascorbate; MDHAR – monodehydroascorbate reductase; PEPcase – phosphenol-pyruvate carboxylase; POD – peroxidase; RuBPCase – Ribulose-bisphosphate carboxylase; SOD – superoxide dismutase Introduction Crop plants in tropical regions like India are fre- quently exposed to varying environmental factors like drought, high temperature and salinity. A consequence of stress-induced-limitation of pho- tosynthesis is the exposure of plants to excess en- ergy, which are harmful because of increased production of active oxygen species (AOS) (Asada 2000; Fryer et al. 2002). Over-production of re- duced and chemically reactive AOS results in oxidative stress and cellular damage (Apel and Hirt 2004). Active oxygen species such as super- oxide (O 2 ) and hydrogen peroxide (H 2 O 2 ) lead to production of hydroxyl radical which is extremely reactive and initiates the peroxidation of Plant Growth Regulation 44: 157–163, 2004. Ó 2004 Kluwer Academic Publishers. Printed in the Netherlands. 157