Abstract
Cadmium (Cd) and lead (Pb) are recognized as the most toxic metal ions due to their detrimental effects not only to plants, but also to humans. The objective of this study was to investigate the effects of Cd and Pb treatments on seed germination, plant growth, and physiological response in tall fescue (Festuca arundinacea Schreb.). We employed six treatments: CK (nutrient solution as control), T1 (1000 mg L-1 Pb), T2 (50 mg L-1 Cd), T3 (150 mg L-1 Cd), T4 (1000 mg L-1 Pb+50 mg L-1 Cd), T5 (1000 mg L-1 Pb+150 mg L-1 Cd). Antagonistic and synergistic actions were observed in tall fescue under Pb and Cd combined treatments. Under low Cd, plants exhibited higher relative germination rate, germ length, VSGR, catalase (CAT) and peroxidase (POD) activities. Additionally, in the shoots, the gene expression level of Cu/Zn SOD, FeSOD, POD, GPX, translocation factors, MDA, EL, and soluble protein contents were reduced under Pb stress. Conversely, under high Cd level, there was a decline in NRT, Pb content in shoots, Pb translocation factors, CAT activity; and an increase in VSGR, Pb content in roots, gene expression level of Cu/ZnSOD and POD in tall fescue exposed to Pb2+ regimes. On the other hand, tall fescue plants treated with low Cd exhibited lower relative germination rate, germination index, germ length, NRT, Cd content in roots. On the other hand there was higher Cd content, Cd translocation factor, CAT and POD activities, and gene expression level of Cu/Zn SOD, FeSOD, POD, GPX under Pb treatment compared with single Cd2+ treatment in the shoots. However, after high Cd exposure, plants displayed lower NRT, Cd content, CAT activity, and exhibited higher Cd contents, Cd translocation factor, MDA content, gene expression level of Cu/ZnSOD and GPX with the presence of Pb2+ relative to single Cd2+ treatment. These findings lead to a conclusion that the presence of low Cd level impacted positively towards tall fescue growth under Pb stress, while high level of Cd impacted negatively. In summary, antioxidant enzymes responded to Cd and Pb interaction at an early stage of exposure, and their gene expression profiles provided more details of the activation of those systems.
Highlights
Soil contamination by heavy metals due to increased human activities including mining, industry activities, transportation, and agriculture raises major global environmental and human health concern [1]
It was suggested that heavy metal tolerance depended on the ability of plants to maintain a balance between the production of toxic oxygen derivatives and capacity of antioxidative defense systems to scavenge [10]
TzureMeng et al [17] reported that there was an induction in the activities of FeSOD, ascorbate peroxidase (APX), and Glutathione reductase (GR) in the marine macroalga Ulva fasciata to alleviate the oxidative damage under Cd stress
Summary
Soil contamination by heavy metals due to increased human activities including mining, industry activities, transportation, and agriculture raises major global environmental and human health concern [1] Due to their toxicity and non- biodegradability metal ions pose a threat to plants by accumulating in edible parts which eventually could enter into the foodchain posing threat to human health [2]. Studies have rigorously documented that ROS are potentially harmful to the cell due to their oxidative damage to cellular structure and function [8] To alleviate this oxidative damage, plants have developed a complex antioxidative defense system, including low-molecular mass antioxidants as well as antioxidative enzymes, such as catalase (CAT), peroxidases (POD), superoxide dismutase (SOD), ascorbate peroxidase (APX) [9, 10]. TzureMeng et al [17] reported that there was an induction in the activities of FeSOD, APX, and Glutathione reductase (GR) in the marine macroalga Ulva fasciata to alleviate the oxidative damage under Cd stress
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