Insights into citric acid-induced cadmium tolerance and phytoremediation in Brassica juncea L.: Coordinated functions of metal chelation, antioxidant defense and glyoxalase systems.

Cadmium (Cd) is a serious environmental threat because it accumulates in plants from soil and is subsequently transported into the food cycle. Increased Cd uptake in plants disrupts plant metabolism and hampers crop growth and development. Therefore, remediation of Cd from soil and enhancing plant tolerance to metal toxicity is vital. In the present study, we investigated the function of different doses of citric acid (CA) on Cd toxicity in terms of metal accumulation and stress tolerance in mustard (Brassica juncea L.). Brassica juncea seedlings (12-day-old) were treated with Cd (0.5mMCd and 1.0mM CdCl2) alone and in combination with CA (0.5mM and 1.0mM) in a semi-hydroponic medium for three days. Cadmium accumulation in the roots and shoots of the mustard seedlings increased in a dose-dependent manner and was higher in the roots. Increasing the Cd concentration led to reduced growth, biomass, water status, and chlorophyll (chl) content resulting from increased oxidative damage (elevated malondialdehyde, MDA content; hydrogen peroxide, H2O2 level; superoxide, O2•- generation; lipoxygenase, LOX activity; and methylglyoxal, MG content) and downregulating of the major enzymes of the antioxidant defense and glyoxalase systems. Under Cd stress, both doses of CA improved the growth of the plants by enhancing leaf relative water content (RWC) and chl content; reducing oxidative damage; enhancing the pool of ascorbate (AsA) and glutathione (GSH) and the activities of the antioxidant enzymes (ascorbate peroxidase, APX; monodehydroascorbate reductase, MDHAR; dehydroascorbate reductase, DHAR; glutathione reductase, GR; glutathione peroxidase, GPX; superoxide dismutase, SOD; catalase, CAT); improving the performance of the glyoxalase system (glyoxalase I, Gly I and glyoxalase II, Gly II activity); and increasing the phytochelatin (PC) content. Exogenous CA also increased the root and shoot Cd content and Cd translocation from the roots to the shoots in a dose-dependent manner. Our findings suggest that CA plays a dual role in mustard seedlings by increasing phytoremediation and enhancing stress tolerance through upregulating the antioxidant defense and glyoxalase systems.

Mahmud JA ，Hasanuzzaman M ，Nahar K ，Bhuyan MHMB ，Fujita M ... -  《-》

γ-aminobutyric acid (GABA) confers chromium stress tolerance in Brassica juncea L. by modulating the antioxidant defense and glyoxalase systems.

Mahmud JA ，Hasanuzzaman M ，Nahar K ，Rahman A ，Hossain MS ，Fujita M ... -  《-》

Maleic acid assisted improvement of metal chelation and antioxidant metabolism confers chromium tolerance in Brassica juncea L.

Chromium (Cr) is a highly toxic environmental pollutant that negatively affects plant growth and development. Thus, remediating Cr from soil or increasing plant tolerance against Cr stress is urgent. Organic acids are recognized as agents of phytoremediation and as exogenous protectants, but using maleic acid (MA) to attain these results has not yet been studied. Therefore, our study investigated the effects of MA on Cr uptake and mitigation of Cr toxicity. We treated 8-d-old Indian mustard (Brassica juncea L.) seedlings with Cr (0.15mM and 0.3mM K2CrO4, 5 days) alone and in combination with MA (0.25mM) in a semi-hydroponic medium. Under Cr stress, plants accumulated Cr in both the roots and shoots in a dose-dependent manner, where the roots showed higher accumulation. Chromium stress reduced the growth and biomass of the Indian mustard plants by reducing water status and photosynthetic pigments, and increased oxidative damage due to generation of toxic reactive oxygen species (ROS) and methylglyoxal (MG). Chromium stress also interfered with the function of the antioxidant defense and glyoxalase systems. However, using MA in the Cr-stressed plants further increased Cr uptake in the roots, but it slightly reduced the translocation of Cr from the roots to the shoots at a lower dose of Cr and significantly at a higher dose. Moreover, MA also increased the other non-protein thiols (NPTs) containing phytochelatin (PC) content of the seedlings, which reduced Cr toxicity. Supplementing the stressed plants with MA upregulated the non-enzymatic antioxidants (ascorbate, AsA; glutathione, GSH); the activities of the enzymatic antioxidants including ascorbate peroxidase (APX), monodehydroascorbate reductase (MDHAR), dehydroascorbate reductase (DHAR), glutathione reductase (GR), glutathione peroxidase (GPX), superoxide dismutase (SOD), and catalase (CAT); and the enzymes of the glyoxalase system including glyoxalase I (Gly I) and glyoxalase II (Gly II); and finally reduced oxidative damage and increased the chlorophyll content and water status as well the growth and biomass of the plants. Our findings suggested two potential uses of MA: first, enhancing phytoremediation, principally phytostabilization and second, working as an exogenous protectant to enhance Cr tolerance.

Mahmud JA ，Hasanuzzaman M ，Nahar K ，Rahman A ，Hossain MS ，Fujita M ... -  《-》

Exogenous sodium nitroprusside and glutathione alleviate copper toxicity by reducing copper uptake and oxidative damage in rice (Oryza sativa L.) seedlings.

Mostofa MG ，Seraj ZI ，Fujita M 《-》

Physiological and biochemical mechanisms of spermine-induced cadmium stress tolerance in mung bean (Vigna radiata L.) seedlings.

Nahar K ，Rahman M ，Hasanuzzaman M ，Alam MM ，Rahman A ，Suzuki T ，Fujita M ... -  《-》