Methyl Jasmonate Alleviates Cadmium-Induced Photosynthetic Damages through Increased S-Assimilation and Glutathione Production in Mustard

Abstract

The effect of methyl jasmonate (MeJA) in mitigation of 50 μM cadmium (Cd) toxicity on structure and function of photosynthetic apparatus in presence or absence of 1.0 mM [Formula: see text] was investigated in mustard (Brassica juncea L. cv. Ro Agro 4001) at 30 days after sowing. Plants exhibited increased oxidative stress, impaired photosynthetic function when grown with Cd, but MeJA in presence of sulfur (S) more prominently ameliorated Cd effects through increased S-assimilation and production of reduced glutathione (GSH) and promoted photosynthetic functions. The transmission electron microscopy showed that MeJA protected chloroplast structure against Cd-toxicity. The use of GSH biosynthetic inhibitor, buthionine sulfoximine (BSO) substantiated the findings that ameliorating effect of MeJA was through GSH production. MeJA could not alleviate Cd effects when BSO was used due to unavailability of GSH even with the input of S. The study shows that MeJA regulates S-assimilation and GSH production for protection of structure and function of photosynthetic apparatus in mustard plants under Cd stress.

Keywords: cadmium toxicity; glutathione; methyl jasmonate; oxidative stress; photosynthesis.

FIGURE 1

Content of Cd (A), H₂O₂ (B), and TBARS (C) in mustard (Brassica juncea L.) leaves at 30 days after sowing (DAS) in leaves originated from plants treated with/without 50 μM Cd, 1.0 mM ${\mathrm{SO}}_{\mathrm{4}}^{\mathrm{2–}}$ (S) or 10 μM MeJA individually or in combinations. Data are presented as treatments mean ± SE (n = 4). Data followed by same letter are not significantly different by least significant difference (LSD) test at P < 0.05 and P < 0.01. Capital letters indicate significance at P < 0.01 and small letters at P < 0.05. nd, not determined; Cd, cadmium; MeJA, methyl jasmonate; TBARS, thiobarbituric acid reactive substances.

FIGURE 2

Activity of SOD (A), APX (B), and GR (C) in mustard (B. juncea L.) leaves treated with 10 μM MeJA and/or grown with 1.0 mM ${\mathrm{SO}}_{\mathrm{4}}^{\mathrm{2–}}$ (S) in presence or absence of 50 μM Cd at 30 DAS. Data are presented as treatments mean ± SE (n = 4). Data followed by same letter are not significantly different by LSD test at P < 0.05 and P < 0.01. Capital letters indicate significance at P < 0.01 and small letters at P < 0.05. APX, ascorbate peroxidase; Cd, cadmium; GR, glutathione reductase; MeJA, methyl jasmonate; SOD, superoxide dismutase.

FIGURE 3

Activity of ATP-S (A), content of S (B), and GSH (C) in mustard (B. juncea L.) leaves treated with 10 μM methyl jasmonate (MeJA) and/or grown with 1.0 mM ${\mathrm{SO}}_{\mathrm{4}}^{\mathrm{2–}}$ (S) in presence or absence of 50 μM Cd at 30 DAS. Data are presented as treatments mean ± SE (n = 4). Data followed by same letter are not significantly different by LSD test at P < 0.05 and P < 0.01. Capital letters indicate significance at P < 0.01 and small letters at P < 0.05. ATP-S, ATP-sulfurylase; Cd, cadmium; GSH, reduced glutathione; MeJA, methyl jasmonate; S, sulfur.

FIGURE 4

Maximum PSII efficiency (A), intrinsic PSII efficiency (B), actual PSII efficiency (C), photochemical quenching (D), non-photochemical quenching (E), and electron transport rate (F) in mustard (B. juncea L.) leaves treated with 10 μM MeJA and/or grown with 1.0 mM ${\mathrm{SO}}_{\mathrm{4}}^{\mathrm{2–}}$ (S) in presence or absence of 50 μM Cd at 30 DAS. Data are presented as treatments mean ± SE (n = 4). Data followed by same letter are not significantly different by LSD test at P < 0.05 and P < 0.01. Capital letters indicate significance at P < 0.01 and small letters at P < 0.05. Cd, cadmium; MeJA, methyl jasmonate.

FIGURE 5

Ultrastructure of chloroplasts from leaves of mustard (B. juncea L.). Transmission electron microscopy micrographs on the representative chloroplasts from the leaves of mustard performed on the control (A,B); 50 μM Cd (C,D) and 1.0 mM ${\mathrm{SO}}_{\mathrm{4}}^{\mathrm{2–}}$ (S) and 10 μM MeJA with 50 μM Cd (E,F) at 30 DAS. Ultrathin sections were prepared, stained with uranyl acetate and lead citrate, and examined by transmission electron microscopy operated at voltage of 120 kV and magnification of 6000× and 1200×. Bar represents 100 nm in the panels (A,C,E) and 500 nm in the panels (B,D,F). Thy, thylakoid membranes; Cd, cadmium; MeJA, methyl jasmonate.

FIGURE 6

Leaf area (A) and plant dry mass (B) of mustard (B. juncea L.) leaves treated with 10 μM MeJA and/or grown with 1.0 mM ${\mathrm{SO}}_{\mathrm{4}}^{\mathrm{2–}}$ (S) in presence or absence of 50 μM Cd at 30 DAS. Data are presented as treatments mean ± SE (n = 4). Data followed by same letter are not significantly different by LSD test at P < 0.05 and P < 0.01. Capital letters indicate significance at P < 0.01 and small letters at P < 0.05. Cd, Cadmium; MeJA, methyl jasmonate.