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Proline and Betaine Reduced the Damage in Maize Caused by Nacl Induced Oxidative Stress

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

Abstract/ Executive Summary:

Proline and betaine are two major organic osmolytes that accumulate in a variety of plant species in response to environmental stresses including salinity and have positive effects on enzyme and membrane integrity along with adaptive roles in mediating osmotic adjustment in plants grown under stress conditions. Recently, it has gain attention of their exogenous application in protecting plants against abiotic stress including salinity. In this study, we checked the effects of exogenous proline and betaine in improving enzymatic and non-enzymatic protective roles in maize. It was found that both proline and betaine made significant delay in leaf water loss and breakdown of chlorophyll components and as well as carotenoids. They showed significant effects in reducing salt induced ROS like super oxide (O₂^•- )_,H₂O₂_,the peroxidation product (MDA), lepoxigenase as well as cytotoxic methyl glyoxal (MG) in maize seedlings. The salinity stress significantly decreased the contents of reduced glutathione (GSH) and ascorbic acid (ASA) concurrently with significant increase in oxidized glutathione (GSSG) and dehydroascorbate (DHA). The application of proline and betaiae improved the glutathione- and ascorbate redox state suggesting their role in reduction of oxidation of GSH and ASA. They increased the activities of antioxidant enzyme like superoxide dismutase (SOD), catalase (CAT), ascorbate peroxidase (APX), glutathione peroxodase (GPX), glutathione reductase (GR), monodehydro ascorbate reductase (MDHAR), dehydroascorbate reductase (DHAR). On the other hand, Proline increased the activities glyoxalse I (Gly-I) and glyoxalase II (Gly-II) while both proline and betaine did not show over expression of glutathione S-transferase (GST) activity and failed to increase peroxidase (POD) activity at 5 and 7 day stress. Taken together, it could be suggested that both proline and betaine showed protective role by increasing antioxidants and detoxification enzymes. However, proline showed better performance than betaine.

Keywords: Proline and betaine, Oxidative damage, Maize, NaCl stress

Location: BARI, Gaipur

Start Date: 30-11-2013

End Date: 30-06-2014

Program Area: Risk Management in Agriculture

Non-commodity: Maize

Objectives:

To understanding the stress tolerance mechanism under saline stress

Methodology:

Plant materials and stress treatments:

Seedlings of BARI hybrid maize 7 were used as plant material. Maize seedlings were grwon in plastic pots. Seven days old seedlings were subjected to stress implementation. Salinaty levels of 16 ds/m were mainetained by adding NaCl and water. A control treatment (with adding NaCl) was also maintained under same condition. In NaCl stressed seedlings 15 mM proline and 15 mM betaine were applied as foliar spray twice daily.Leaf relative water content (RWC), contents of chlorophyll and carotenoid, ascorbate and glutathioneExtraction 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 and 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: 127-145

Article Link (Online Journal):

Funding Source:

1. Government

Budget: Two lacs

Total Budget (Tk.) : Two lacs

Achievement/Findings:

Both proline and betaine maintained the salinity reduced RWC, Chl and Carotinoid. Saline stress sharply and continuously increased the endogenous proline contents in maize seedlings Exogenous application of proline further increased the endogenous proline by 25, 16, 18 and 21% over saline stress at 1, 3, 5 and 7 day, respectively. In case of betaine treatment in saline treated seedlings, the increment was very low. The formation rate of O₂^•- and the content of H₂O₂_, MDA, MG and LOX increased continuously and significantly with duration of saline stress. Application of proline reduced the contents. Both proline and betaine maintained the GSH and ASA higher under saline stress.Under saline stress the activity of SOD and POD increased with or without proline and betaine. Saline stress decreased the activities of CAT compared to control, though they were statistically similar. At later stage of stress, CAT activities were observed to increase. In case of APX, the saline stress decreased the activities continuously with stress duration. Proline and betaine supplementation in saline stressed seedlings maintained the activities higher in stressed seedling Saline stresses increased the GPX activity GR activities. Both proline and betaine maintained the GR activities higher in saline stressed seedlings. Saline stress increased MDHAR activity subsequently decreased gradually after 1 day. On the other hand, DHAR activity increased up to 5 day saline stress Proline and betaine increased MDHAR and DHAR activities.

Remarkable increase was observed in GST activities in maize seedlings under salinity stress with and without proline and betaine. Application of proline in saline treated seedlings decreased the MG contents over saline treatment. In response of saline stress, after 1 day Gly-I activity remained subsequently decreased with duration. Though exogenous proline increased the activity significantly, betaine failed to do so.

Knowledge Management: Report/Proceedings