Influence of Methyl Jasmonate and Short-Term Water Deficit on Growth, Redox System, Proline and Wheat Germ Agglutinin Contents of Roots of Wheat Seedlings

Abstract

Drought is a serious environmental problem that limits the yield of wheat around the world. Using biochemical and microscopy methods, it was shown that methyl jasmonate (MeJA) has the ability to induce the oxidative stress tolerance in roots of wheat plants due to the regulation of antioxidant enzymes activity, proline (Pro), and wheat germ agglutinin (WGA) accumulation. During the first hours of 12% polyethylene glycol (PEG) exposure, stress increased the superoxide radical (O₂^•-) and the hydrogen peroxide (H₂O₂) accumulation, the activity of superoxide dismutase (SOD), total peroxidase (POD), ascorbate peroxidase (APX), catalase (CAT), the percent of dead cells (PDC), malondialdehyde accumulation (MDA), and electrolyte leakage (EL) of wheat roots as compared to the control. Stress enhanced proline (Pro) and wheat germ agglutinin (WGA) contents in roots and the plant's nutrient medium, as well as decreased the mitotic index (MI) of cells of root tips in comparison to the control. During PEG exposure, 10^-7 M MeJA pretreatment increased the parameter of MI, declined O₂^•- and H₂O₂ generation, PDC, MDA, and EL parameters as compared to MeJA-untreated stressed seedlings. During 1 day of drought, MeJA pretreatment additionally increased the activity of SOD, total POD, APX, CAT, Pro, and WGA accumulation in wheat roots in comparison to MeJA-untreated stressed plants. During stress, MeJA pretreatment caused a decrease in Pro exudation into the growth medium, while WGA content in the medium was at the control level.

Keywords: Triticum aestivum L.; catalase; hydrogen peroxide; methyl jasmonate; peroxidase; polyethylene glycol 6000; proline; superoxide dismutase; superoxide radical; wheat germ agglutinin.

Figure 1

The effect of exogenous 10⁻⁷ M MeJA treatment on superoxide radical accumulation in roots (a), exudation of O₂^•− (b), accumulation of hydrogen peroxide in roots (c), and H₂O₂ excretion into the growth medium (d) of 6-day-old wheat plants. Data are given as mean values and their standard errors from three biological and four analytical repeats. Lowercase letters above the columns indicate significant differences between variants of treatment at the particular time point at p < 0.05 (ANOVA, LSD test). Capital letters indicate significant differences for the same treatment at different time points at p < 0.05 (ANOVA, LSD test). FW—fresh weight; MeJA—methyl jasmonate.

Figure 2

The influence of exogenous 10⁻⁷ M MeJA treatment for 0.5–5 h on superoxide dismutase (SOD, (a)), total peroxidase (POD, (b)), ascorbate peroxidase (APX, (c)), and catalase (CAT, (d)) activities in roots of 6-day-old wheat. Data are given as mean values and their standard errors from three biological and four analytical repeats. Lowercase letters above the columns indicate significant differences between variants of treatment at the particular time point at p < 0.05 (ANOVA, LSD test). Capital letters indicate significant differences for the same treatment at different time points at p < 0.05 (ANOVA, LSD test).

Figure 3

The effect of exogenous 10⁻⁷ M MeJA treatment on coefficients of SOD/superoxide radical (a), total POD/hydrogen peroxide (b), APX/H₂O₂ (c), and CAT/hydrogen peroxide (d) of roots of 6-day-old wheat plants. Data are given as mean values and their standard errors. Lowercase letters above the columns indicate significant differences between variants of treatment at the particular time point at p < 0.05 (ANOVA, LSD test). Capital letters indicate significant differences for the same treatment at different time points at p < 0.05 (ANOVA, LSD test).

Figure 4

The influence of exogenous 10⁻⁷ M MeJA pretreatment for 24 h followed by 12% PEG exposure for 24 h on the percentage of dead cells (a) and mitotic index of cells (MI, (b)) of roots of 8-day-old wheat plants. Values are the mean of three replicates ± SE. To assess the level of PDC n = 10, to estimate the level of MI, n = 1500. Means are considered different at p ≤ 0.05 when they are followed by different letters within the same parameter.

Figure 5

The effect of 10⁻⁷ M MeJA pretreatment for 24 h followed by 12% PEG exposure for 0.5–4 h on superoxide anion accumulation in wheat roots (a) and in the growth medium (b), hydrogen peroxide generation in the roots (c) and H₂O₂ accumulation in the growth medium (d) of 7-day-old wheat plants. Data are given as mean values and their standard errors from three biological and four analytical repeats. Lowercase letters above the columns indicate significant differences between variants of treatment at the particular time point at p < 0.05 (ANOVA, LSD test). Capital letters indicate significant differences for the same treatment at different time points at p < 0.05 (ANOVA, LSD test).

Figure 6

The influence of 10⁻⁷ M MeJA pretreatment for 24 h followed by 12% PEG exposure for 0.5–5 h on superoxide dismutase (SOD, (a)), total peroxidase (POD, (b)), ascorbate peroxidase (APX, (c)), and catalase (CAT, (d)) activities in roots of 7-day-old wheat seedlings. Data are given as mean values and their standard errors from three biological and four analytical repeats. Lowercase letters above the columns indicate significant differences between variants of treatment at a particular time point at p < 0.05 (ANOVA, LSD test). Capital letters indicate significant differences for the same treatment at different time points at p < 0.05 (ANOVA, LSD test).

Figure 7

The effect of 10⁻⁷ M MeJA pretreatment for 24 h followed by 12% PEG exposure for 0.5–4 h on coefficients of SOD activity/superoxide radical (a), total POD activity/hydrogen peroxide (b), APX activity/hydrogen peroxide (c), and CAT activity/hydrogen peroxide (d) in roots of 7-day-old wheat seedlings. Data are given as mean values and their standard errors. Lowercase letters above the columns indicate significant differences between variants of treatment at the particular time point at p < 0.05 (ANOVA, LSD test). Capital letters indicate significant differences for the same treatment at different time points at p < 0.05 (ANOVA, LSD test).

Figure 8

Representative images illustrating in situ histochemical localization of lipid peroxidation (a), and relative quantification assay of the products of lipid peroxidation (b) in tips of 8-day-old wheat roots after 10⁻⁷ M MeJA pretreatment for 24 h, followed by 12% PEG exposure for 24 h. Scale bar = 200 µm. Image J software 1.41o/Java 1.6.0_10 (NIH, Bethesda, MD, USA) was used to calculate the relative level of lipid peroxidation by integrated density. Data are the mean ± SE (n = 10). Different letters above the columns imply that the values differ significantly at p < 0.05 (ANOVA, LSD test).

Figure 9

The effect of 10⁻⁷ M MeJA pretreatment for 24 h followed by 12% PEG exposure for 24 h on WGA accumulation in roots (a), and WGA excretion into the growth medium (b) of 8-day-old wheat seedlings. WGA—wheat germ agglutinin. Data are the mean ± SE (n = 9). Different letters above the columns imply that the values differ significantly at p < 0.05 (ANOVA, LSD test).

Figure 10

Cellular WGA localization in transverse sections of the proximal part of roots of 7-day-old wheat seedlings grown under 10⁻⁷ M MeJA pretreatment for 24 h and subsequent 12% PEG exposure for 5 h. (a)—control; (b)—(MeJA); (c)—12% PEG; (d)—(MeJA) + PEG. The bar on the right side of the image represents the WGA values converted into false color of fluorescence intensity (FI) scale. Bar scale = 30 µm.

Figure 11

The correlation coefficient matrices for all examined parameters of 6-day-old wheat plants under 10⁻⁷ M MeJA application. The matrices are colored by magnitude and parity (green positive and red negative) for correlations at a p < 0.05 significance level.

Figure 12

The correlation coefficient matrices for all examined parameters of 7–8-day-old wheat seedlings subjected to MeJA pretreatment and drought stress, caused by 12% PEG. The matrices are colored by magnitude and parity (green positive and red negative) for correlations at a p < 0.05 significance level.