Abstract
This work examined the role of exogenously applied calcium (Ca; 50 mM) and potassium (K; 10 mM) (alone and in combination) in alleviating the negative effects of cadmium (Cd; 200 μM) on growth, biochemical attributes, secondary metabolites and yield of chickpea (Cicer arietinum L.). Cd stress significantly decreased the length and weight (fresh and dry) of shoot and root and yield attributes in terms of number of pods and seed yield (vs. control). Exhibition of decreases in chlorophyll (Chl) a, Chl b, and total Chl was also observed with Cd-exposure when compared to control. However, Cd-exposure led to an increase in the content of carotenoids. In contrast, the exogenous application of Ca and K individually as well as in combination minimized the extent of Cd-impact on previous traits. C. arietinum seedlings subjected to Cd treatment exhibited increased contents of organic solute (proline, Pro) and total protein; whereas, Ca and K-supplementation further enhanced the Pro and total protein content. Additionally, compared to control, Cd-exposure also caused elevation in the contents of oxidative stress markers (hydrogen peroxidase, H2O2; malondialdehyde, MDA) and in the activity of antioxidant defense enzymes (superoxide dismutase, SOD; catalase, CAT; ascorbate peroxidase, APX; glutathione reductase, GR). Ca, K, and Ca + K supplementation caused further enhancements in the activity of these enzymes but significantly decreased contents of H2O2 and MDA, also that of Cd accumulation in shoot and root. The contents of total phenol, flavonoid and mineral elements (S, Mn, Mg, Ca and K) that were also suppressed in Cd stressed plants in both shoot and root were restored to appreciable levels with Ca- and K-supplementation. However, the combination of Ca + K supplementation was more effective in bringing the positive response as compared to individual effect of Ca and K on Cd-exposed C. arietinum. Overall, this investigation suggests that application of Ca and/or K can efficiently minimize Cd-toxicity and eventually improve health and yield in C. arietinum by the cumulative outcome of the enhanced contents of organic solute, secondary metabolites, mineral elements, and activity of antioxidant defense enzymes.
Highlights
Cadmium (Cd), a naturally occurring element having no known beneficial role is a highly toxic environmental pollutant (Mobin and Khan, 2007; Shamsi et al, 2008; Asgher et al, 2015)
The shoot Fresh weight (FW) and dry weight (DW) were elevated by the supplementation of Ca and K and the maximum increase in shoot FW and DW was 30.59 and 20.60%, respectively with Cd + Ca + K treatment compared to plants treated with Cd alone (Table 1)
The root FW and DW increased with addition of Ca and K and the highest increase in root FW (30.98%) and root DW (24.41%) was observed at Cd + Ca + K treatment over the plants treated with Cd alone (Table 1)
Summary
Cadmium (Cd), a naturally occurring element having no known beneficial role is a highly toxic environmental pollutant (Mobin and Khan, 2007; Shamsi et al, 2008; Asgher et al, 2015). Tissue/organ-Cd-burden can alter carbohydrates, proline (Pro) and protein contents (Siddique et al, 2012; Abdel Latef, 2013; El-Beltagi and Mohamed, 2013; Mondal, 2013), perturb the absorption of nutrients such as N, P, K, Ca, Mg, Mn, Cu, Zn, Fe, and Ni (Sandalio et al, 2001; Siddique et al, 2012; Abdel Latef, 2013), and can elevate the reactive oxygen species (ROS) levels (Ahmad et al, 2010, 2015). The lipid peroxidation is generally reflected by increased concentration of malondialdehyde (MDA) content (Abdel Latef, 2013; Ahmad et al, 2015; Anjum et al, 2015)
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