Reactive oxygen species, antioxidant enzyme activities and gene expression patterns in leaves and roots of Kentucky bluegrass in response to drought stress and recovery

The objective of this study was to investigate accumulation of reactive oxygen species, antioxidant enzyme activities, and gene expression patterns of antioxidant enzymes of Kentucky bluegrass (Poa pratensis L.) under drought stress and recovery. Grass (c.v. Midnight II) was subjected to soil drying for 5d and then rewatered for 1d in growth chambers. Drought stress increased superoxide (021 production of leaves and hydrogen peroxide (H2O2) content of the leaves and roots. Recovery enhanced leaf O-2(-) production and root H2O2 content. Lipid peroxidation of the roots increased 4.5-fold and 2.4-fold under drought stress and recovery, respectively. Drought stress increased the leaf activities of ascorbate peroxidase (APX, EC 1.11.1.11), monodehydroascorbate reductase (MDHAR, EC 1.6.5.4), dehydroascorbate reductase (DHAR, EC 1.8.5.1), and the root activities of catalase (CAT, EC 1.11.1.6), glutathione reductase (GR, EC 1.6.4.2) and MDHAR, while reducing the root activities of superoxide dismutase (SOD, EC 1.15.1.1) and DHAR, respectively. The increased leaf activities of APX, MDHAR, DHAR and the root activities of MDHAR and CAT were observed after rewatering, compared to the control. For the leaves, the expressions of iron SOD (FeSOD), cytosolic copper/zinc SOD (Cu/ZnSOD), chloroplastic Cu/ZnSOD, and DHAR were down-regulated by drought stress but recovered to control level after rewatering, while the expressions of GR and MDHAR were up-regulated and remained that levels after recovery. For the roots, the expressions of cytosolic Cu/ZnSOD, manganese SOD (MnSOD), cytosolic APX, GR, and DHAR were down-regulated under drought stress but recovered except for GR and DHAR, while MDHAR expression was up-regulated. No differences in CAT transcript abundance were noted among the treatments. Antioxidant enzymes and their gene expressions may be differentially or cooperatively involved in the defense mechanisms in the leaves and roots of Kentucky bluegrass exposed to drought stress and recovery. (C) 2008 Elsevier B.V. All rights reserved.