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Protective Roles of Antioxidants in Two Differently Sensitive Maize Inbreds Under Drought

Dr. Md. Motiar Rohman
Senior Scientific Officer
Plant Breeding Division, BARI, Gazipur

Abstract/ Executive Summary:

In this study, the level of oxidative stress and the participation of antioxidant systems were investigated in seedlings of two maize inbreds: E134, a relatively drought tolerant, and E142, a susceptible inbred subjected to water deficit for 7 days and then rewatered, to know the unveil oxidative stress tolerant mechanism under drought. The superoxide (O₂^•-) generation rate, hydrogen peroxide (H₂O₂) and methyl glyoxal (MG) contents were higher throughout the drought period in E142_. Conversely, proline accumulation was remarkably higher in E134. The reduced glutathione (GSH), ascorbic acid (ASA) and their redox homeostasis showed more oxidation in E142. Though the activities of glutathione S-transferase (GST), glyoxalase-I (Gly-I) and glyoxalse-II (Gly-II) increased in both inbreds, GST and Gly-II activities decreased in E142 after recovery. In case of reactive oxygen species (ROS) SCAvenging enzymes, superoxide dismutase (SOD), and peroxidase (POD) activities were higher in E142, while catalase (CAT) activities were higher in E134. Ascorbate peroxidase (APX) and glutathione peroxidase (GPX) activities induced in both inbreds under drought, they decreased in recovery. Glutathione reductase (GR) activity was higher in E134, contrary, DHAR activity being higher in E142. Chlorophyll and carotenoids recovery was higher in E142. Interestingly, both peroxidation product (MDA) and lipoxigenase (LOX) activity were lower in E142. Taken together, the non-enzymatic antioxidant system was stronger in E134, however, the higher SOD and POD, APX and GPX in E142 might involve cellular protection from oxidative damage and lower MDA might be due to lower activity of LOX.

Keywords: Antioxidative protection, Oxidative damage, Maize seedlings, Drought stress

Location: Plant Breeding Division, BARI, Gazipur

Start Date: 30-11-2013

End Date: 30-06-2014

Program Area:

Commodity: Maize

Objectives:

To understanding the stress tolerance mechanism under drought stress

Methodology:

Two preselected maize inbreds: E134, a relatively drought tolerant, and E142, a susceptible inbred subjected to water deficit for 7 days and then rewatered. Seedlings of of the inbreds were prepared in plastic pot and 8 day old seedlings were subjected to stop watering for 7 days and rewatered again for 2 days. Five days after stopping watering was termed as moderate stress and 7 days as severe stress. Data were taken on different parameter in fully expanded leaves on 5 and 7 day of stressed seedlings and 2 days after rewatering. Leaf relative water content (RWC), contents of chlorophyll and carotenoid, ascorbate and glutathione. Extraction of soluble protein: Fresh leaves of maize seedlings were extracted by homogenizing in an equal volume of 25 mM. Tris-HCI buffer (pH 8.0) containing 1 mM EDTA, 1% (w/v) ascorbate and 10% (w/v) glycerol with mortar pestle. The homogenate was centrifuged at 11,500×g for 15 min, and the supernatant was used as a soluble protein solution for enzyme assay. The protein concentration in the leaf extracts was determined according to the method of Bradford (1976) using BSA as a protein standard.Activities of Superoxide dismutase (SOD, EC 1.15.1.1), Peroxidase POD (EC 1.11.1.7), Ascorbate peroxidase (APX, EC: 1.11.1.11), Monodehydroascorbate reductase (MDHAR, EC: 1.6.5.4), Dehydroascorbate reductase (DHAR, EC: 1.8.5.1), Glutathione reductase (GR, EC: 1.6.4.2), Glutathione S-transferase (GST, EC: 2.5.1.18), Glutathione peroxidase (GPX, EC: 1.11.1.9), Catalase (CAT, EC: 1.11.1.6), Glyoxalase I (Gly-I, EC: 4.4.1.5), Glyoxalase II (Gly-II, EC: 3.1.2.6): and Lipoxygenase (LOX, EC: 1.13.11.12) were assyed following stdard methods.

Measurement of the O₂^•− generation rate, H₂O₂, Lipid Peroxidation, Proline and Methyl glyoxalwere done following with standard methods.

All data obtained was analyzed by SAS (Version 9.1) program following complete randomized design (CRD) and the mean differences were compared by lsd tests. P values<0.05 were considered to be significant.

Source of Information: Annual Research Report 2013-14, Plant Breeding Division, BARI, page: 145-163

Article Link (Online Journal):

Funding Source:

1. Government

Budget: Two lacs

Total Budget (Tk.) : Two lacs

Achievement/Findings:

Upon exposure to drought stress, leaf RWC decreased significantly in both inbreds when compared to their controls. Under drought stress the Car contents decreased in both inbreds. In rewatering, Chla, Chlb and Car contents recovered significantly. Drought stress caused a marked increase in endogenous proline content in seedlings of both inbreds; however, the increment was higher in P134 compared to drought sensitive P142. The O₂^•- ion formation rate and contents of H₂O₂and MDA increased continuously with duration of drought stress in both inbreds; however, the production rate was higher in drought sensitive inbred P142. On thr other hand, LOX activity was higher in drought tolerant inbred P134. In rewatering, the contents contents became almost similar to respective controls. The contents of GSH and ASA decreased under drought stress in both inbreds and simultaneous increased the contentds of GSSG and DHA. Rewatering of seedlings reducded the GSSG contents slightly (9 and 15%) over severe stress in P134 and P142, resspectively. However, ASA recovery was higher in P142.

Activities of SOD and POD was higher in P142. On the other hand, CAT and CAT activities remained almost similar in both inbreds. Rewatering of severe stressed seedlings caused significant reduction in APX activity in both inbreds. Drought stresses increased GPX, GR and GST activities in both drought tolerant and were higher in P142. Drought stress increased the MDHAR activities and in both inbreds as compared to control and increased DHAR activity was higher in P134. After rewatering, the activities decreased in almost cases. The content of MG was higher in P142 under stress. In drought sensitive P142, the activity of Gly-I remained almost similar under drought stress, while the activity increased significantly in tolerant inbred P134. The MG contents and glyoxalse activities were found to decrease after rewatering in both inbreds.

Knowledge Management: Report/Proceedings