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Exogenously Applied Proline Modulates Drought Tolerance in Maize (zea Mays L)

Shamim Akram
Soil Science Division, Bangladesh Institute of Nuclear Agriculture, Mymensingh-2202, Bangladesh.

Mohammad Golam Kibria
Department of Soil Science, Bangladesh Agricultural University, Mymensingh-2202, Bangladesh.

Yoshiyuki Murata
Department of Soil Science, Bangladesh Agricultural University, Mymensingh-2202, Bangladesh.

Md. Anamul Hoque
Graduate School of Environmental and Life Science, Okayama University, Okayama 700-8530,Japan.

Abstract/ Executive Summary:

Improving drought stress tolerance in maize is essential to increase its production and yield worldwide. Thus, the present study was conducted to investigate the improvement of drought tolerance in maize (Zea mays L.) by exogenous application of proline (25 and 50mM) on two maize varieties. Maize plants were subjected to drought stress at various phases of plant growth under pot culture conditions and proline was applied as a foliar spray. Water deficit stress caused a significant decrease (by approximately 25%) in the growth and yield of both maize varieties by decreasing plant height, cob length, dry root weight, grains per cob, and 100-grain weight. Water deficit stress also decreased chlorophyll and intercellular proline contents, and antioxidant enzyme activities viz. catalase (CAT), guaiacol peroxidase (POX), and ascorbate peroxidase (APX). Exogenous application of proline (50 mM) was found to be more effective in increasing the growth and yield of both varieties. These increases were positively associated with increased levels (by at least 15%) of chlorophyll and intracellular proline, and enhanced activities of CAT, POX, and APX enzymes in both varieties. Interaction effects of exogenous proline and water deficit stress were significant in aspects of higher growth and yields and enhanced levels of chlorophyll, intracellular proline, and antioxidant enzyme activities. Therefore, it is concluded that foliar application of proline improves drought tolerance by modulating chlorophyll and intracellular proline contents, and antioxidant enzyme activities.

Keywords: Drought stress; Proline; Chlorophyll; Antioxidant enzymes

Location: Department of Soil Science, BAU, Mymensingh.

Start Date:

End Date:

Program Area: Crop-Soil-Water Management

Commodity: Drought, Maize

Objectives:

To investigate the impact of exogenous application of proline on the growth and yield of maize under drought stress conditions.

Methodology:

The pot experiment was carried out at the net- house, Department of Soil Science, BAU, Mymensingh. Two maize cultivars were used as plant materials in this experiment. The total numbers of pots used in this study were 72 (12×3×2). Each plastic pot was 15 cm deep with a 17 cm diameter at the top. The top surface area of each pot was 0.23 m². Each pot contained one plant. Considerable spacing was maintained among the pots for the convenience of management operations. Two maize varieties (BARI Hybrid Maize-5 and BARI Hybrid Maize-9) were used to validate the effect of exogenous application of proline. These two hybrid varieties were selected as they are mostly grown by the farmers in the field. The factorial experiment was carried out in randomized complete block design (RCBD) with three replications. Treatment combinations were applied at the different levels of irrigation and proline. There were four levels of irrigation, viz. I0-control (normal irrigations), I1-water deficit stress at the vegetative stage, I2-water deficit stress at flowering stage, and I3-water deficit stress at vegetative and flowering stages. The 0, 25, and 50mM exogenous proline was applied, denoted as P0, P25, and P50. However, there were twelve treatment combinations, viz. T₁= I₀P₀; T₂= I₀P₂₅; T₃= I₀P₅₀; T₄= I₁P₀; T₅= I₁P₂₅; T₆= I₁P₅₀; T₇= I₂P₀; T₈= I₂P₂₅; T9= I₂P₅₀; T₁₀= I₃P₀; T₁₁= I₃P₂₅ and T₁₂= I₃P₅₀. For the preparation of 25 mM and 50 mM solutions, 2.88 g and 5.76 g of proline powder were dissolved in 1000 ml of water and 1 ml of Tween- 20. Tween-20 was used as a sticky substance that helps proline solutions to prevent droplet formation maintaining close contact with plant leaves. Proline was applied at vegetative and reproductive stages as a foliar spray at a volume of 25 mL per plant per treatment. Chlorophyll and intracellular proline contents were measured from the 2nd and 3rd flag green leaf of maize after 15 days’ exogenous proline application. Chlorophyll content was measured according to a method by Porra et al. 1989). An aliquot amount (0.5 g) of fresh green leaf of maize was suspended in 10 ml of 80% acetone, mixed well, and kept at room temperature in the dark for 7 days. The supernatant was collected after centrifugation at 5000 rpm for 15 min and the absorbance was read at 645 nm and 663 nm in a spectrophotometer. Proline content was measured according to the method of Bates et al. . An aliquot amount (0.5 g) of fresh green leaf of maize was homogenized in 10 ml of 3% sulfosalicylic acid and the homogenate was centrifuged at 5000 rpm for 15 min. Two milliliters of the supernatant were reacted with 2 ml of acid ninhydrin and 2 ml of glacial acetic acid for 1 hr at 100°C. The colored reaction mixture was extracted with 4 ml of toluene and the absorbance was recorded at 520 nm. Proline content was calculated from a standard curve. Performance of antioxidant enzyme activities was measured from green leaves of maize at 15 days after proline application. In this regard, 2 g of the plant materials were homogenized with 10 mL of 0.1M phosphate buffer (pH 6.8) and centrifuged at 2°C for 20 min at 20,000x g in a refrigerated centrifuge. The clear supernatant was used as an enzyme extract. Catalase (CAT) activity was determined by the method of Aebi. The reaction mixture contained50 mM Tris–HCl (pH 8.0), 0.25 mM EDTA, 20 mM H₂O₂ and 25 ml of sample solution. The reaction was started by the addition of H₂O₂. The activity was calculated from the decrease in absorbance at 240 nm for 2 min when the extinction coefficient was 40 M-1 cm-1. Guaiacol peroxidase (POX) activity was determined according to Nakano and Asada. The reaction mixture contained 50 mM KH₂PO₄ buffer (pH 7.0), 0.1 mM EDTA, and 0.1 mM H₂O₂, and 10 mM guaiacol. The reaction was started by the addition of the sample solution to the reaction mixture. The activity was calculated from the change in absorbance at 470 nm for 30 sec where an extinction coefficient was 26.6 mM^-1 cm^-1. Ascorbate peroxidase (APX) activity was estimated following the method of Nakano and Asada. The reaction mixture contained 50 mM KH₂PO₄ buffer (pH 7.0), 0.1 mM EDTA, and 0.1 mM H₂O₂, and 0.5 mM ascorbate. The reaction was started by adding the sample solution to the reaction mixture. The activity was calculated from the change in absorbance at 290 nm for 1 min when the extinction coefficient was 2.8 mM^-1 cm^-1. Data were analyzed statistically using a two-way analysis of variance (ANOVA) to examine the treatment effects. The mean differences were adjudged by Duncan’s Multiple Range Test (DMRT) and ranking was indicated by letters.

Source of Information: International Journal of Plant & Soil Science - 33(19): 198-212, 2021

Article Link (Online Journal): DOI: 10.9734/IJPSS/2021/v33i1930619

Funding Source:

Budget:

Total Budget (Tk.) :

Achievement/Findings:

Water deficit stress caused a significant reduction in growth and development as well as yield of both (BARI Hybrid Maize-5 and BARI Hybrid Maize-9) varieties. Exogenous application of proline application confers tolerance to drought stress in maize cultivars by increasing chlorophyll, endogenous proline contents and enhancing antioxidant defense systems and resulting in increased plant growth and physiological responses.

Knowledge Management: Journal