Abstract
The presence of Cadmium (Cd) in the agricultural soils affects horticultural cultivars and constrains the crop productivity. A pot experiment was performed using five cultivars of mustard (Brassica juncea L.) to evaluate the difference in their response to Cd toxicity under greenhouse conditions. The pots containing reconstituted soil were supplied with different concentration of CdCl2 (0, 25, 50, 100 or 150 mg Cd kg-1 soil). Increasing concentration of Cd in the soil resulted in decreased growth, photosynthesis and yield. Maximum significant reduction in growth, photosynthesis and yield were observed with 150 mg Cd kg-1 soil in all the cultivars. Our results indicate that the cultivar Alankar is found to be more tolerant to Cd stress, recording higher plant dry mass, net photosynthesis rate, associated with high antioxidant activity and low Cd content in the plant leaves and thus less oxidative damage. Cultivar RH30 experienced maximum damage in terms of reduction in growth, photosynthesis, yield characteristics and oxidative damage and emerged as sensitive cultivar. The data of tolerance index of Alankar were found to be higher among all tested mustard cultivars which indicate its higher tolerance to Cd. Better coordination of antioxidants protected Alankar from Cd toxicity, whereas lesser antioxidant activity in RH30 resulted in maximum damage. Cultivars of mustard were ranked with respect to their tolerance to Cd: Alankar>Varuna>Pusa Bold>Sakha>RH30, respectively.
Introduction
Agricultural soils worldwide are slightly to moderately contaminated with toxic heavy metals that restrict the crop plants to reach their full genetic potential and cause significant loss by reducing the crop productivity.1 Among heavy metals, Cd is a non-essential and most deleterious heavy metal pollutant commonly released into the arable soil from various industrial, mining and farming practices,2 and has been ranked No. 7 among the top 20 toxins which affect the human health by entering in the food chain.3,4 Although Cd is a highly phytotoxic metal, it is easily taken up by plant roots growing on Cd-contaminated soils and transported to above ground plant parts.5–7 The regulatory limit of Cd in agricultural soils is 100 mg Cd kg−1 soil,8 but this threshold is continuously increasing because of anthropogenic and industrial activities. Plants growing on Cd contaminated soil result in Cd accumulation in all plant parts, which inhibits plant growth, affect nutrient uptake, alters the chloroplast ultrastructure, inactivates enzymes of CO2 fixation, inhibits photosynthesis and induces lipid peroxidation and antioxidant machinery.4,9–11 However, Cd is a non redox-active metal, but it induces the generation of reactive oxygen species (ROS) including superoxide radical (O2•−), hydrogen peroxide (H2O2) and hydroxyl radical (OH•).12 This can cause cell death due to oxidative stress such as membrane lipid peroxidation, protein oxidation, enzyme inhibition and damage to nucleic acids.4,12–14 To repair the Cd-induced inhibitory effects of ROS, plants employ ROS-detoxifying antioxidant defense mechanisms. Among antioxidative enzymes, superoxide dismutase (SOD; EC, 1.15.1.1) constitutes the primary step of cellular defense and dismutates O2•− to H2O2 and O2. Further, the accumulation of H2O2 is restricted through the action of catalase (CAT; EC, 1.11.1.6) or by the ascorbate-glutathione cycle, where ascorbate peroxidase (APX; EC, 1.11.1.11) is converted to H2O. Finally, glutathione reductase (GR; EC, 1.6.4.2) catalyzes the NADPH-dependent reduction of oxidized GSSG to the reduced GSH.12,15 It has been reported that Cd toxicity in crop plants is found to be associated with the ability of antioxidant machinery to scavenge Cd-induced production of excessive ROS.12
Cd is toxic for most of the important crop plants at concentrations more than 5–10 µg Cd g−1 leaf dry weight except some of the Cd-hyperaccumulators which can tolerate Cd concentrations of 100 µg Cd g−1 leaf dry weight.16–18 However, Cd is toxic to plants even at low concentration in the soils but its phytotoxicity varies with the concentration of Cd in the soil as well as with the plant species and cultivars. Some plant species or cultivars have developed tolerance to Cd. It has been found that cultivars differ in their ability to detoxify Cd in between and within the plant species, which plays a significant role in the expression of high tolerance in crop plants to Cd toxicity.19–21 Therefore smart selection of plant cultivars with the ability to tolerate Cd in the soil could be the best strategy to counteract the inhibitory effects of Cd in crop plants. Five cultivars of Indian mustard (Brassica juncea L.) were used in the present study to evaluate their relative tolerance to Cd toxicity on the basis of growth, photosynthesis, yield characteristics and antioxidant enzyme activity in the presence of different Cd concentrations in the soil (0, 25, 50, 100 or 150 mg Cd kg−1 ).
Results and Discussion
Industrial and agricultural practices have led to an increased level of Cd in the agricultural soil. The contamination of agricultural soils with Cd is of great concern because it causes reductions of plant growth, metabolism and productivity worldwide.4 It is established that plant cultivars differs in their tolerance to Cd toxicity, therefore, in the present investigation five Indian mustard cultivars were screened for their tolerance potential under different Cd treatments by evaluating the growth, photosynthesis, antioxidant capacity and yield performance. Increasing concentration of Cd in the soil adversely affected the growth, photosynthesis, metabolism and yield of all the five mustard cultivars tested in the present study (Figs. 1 and 2). The growth attributes such as shoot length, root length, leaf area and plant dry mass were maximally and significantly reduced by 150 mg Cd kg−1 soil (Fig. 1A–D). Roots were found to be more sensitive to Cd toxicity than shoots. Cd-induced reduction in plant growth has also been reported previously in references 4, 10, 19, 22 and 23. The inhibitory effect of Cd on growth characteristics was more evident on RH30 and least in Alankar. Similar to growth, maximum significant reduction in photosynthetic characteristics like PN, gs, CA activity and Chl content was also noted with higher Cd in the soil (150 mg Cd kg−1 soil) (Fig. 1E–H). However, Cd at a concentration of 25 mg Cd kg−1 soil exerted no change on the growth and photosynthetic characteristics of all the cultivars. The order of performance of cultivars in terms of percent reduction in growth and photosynthetic characteristics was Alankar > Varuna > Pusa > Bold > Sakha >RH30. The tolerance index of all the cultivars calculated using the data of plant dry mass also suggested the same trend of cultivar performance under Cd stress (Fig. 2C). As observed in the present study, the growth inhibition may be consequence of Cd interference with the vital metabolic processes such as photosynthesis and translocation of photosynthetic products and essential nutrients.4,10,22–24 Cd stress significantly reduced the photosynthetic characteristics, such as PN, gs, CA activity and Chl content. The extent of reduction in photosynthetic characteristics was found to be higher in RH30 among all cultivars. The PN, gs, CA activity and Chl content were reduced to 53.57%, 57.81%, 67.50% and 60.15%, respectively, in comparison to control, whereas 37.66%, 40.32%, 40.68% and 44.44% reduction was noted in the cultivar Alankar under 150 mg Cd kg−1 soil. Cd-induced inhibition of PN may be due to the reduction of gs and photosynthetic pigment content, as well as reduced CA activity. Previous studies have also reported reduction in photosynthesis under Cd stress.4,19,22,25 Siedlecka et al. reported that Cd affects photosynthesis by inhibiting different reaction steps of Calvin-cycle. Significant reduction in net photosynthetic rate, stomatal conductance, Rubisco activity, CA activity and chlorophyll content was noted in the presence of Cd.10,19,22,27,28 Cd is found to inhibit Chl biosynthesis by means of a reaction with the thiol groups of the enzymes of 5-aminolevulinic acid synthesis and protochlorophyllide reductase complex.29 Substitution of Mg2+ ion of the Chl molecule by Cd, Cu, Zn, Pb, Ni, Zn or Hg may be reason of arrested photosynthesis.30 Yield characteristics were also found to be reduced by Cd in the soil in all the cultivars. Maximum reduction in yield characteristics was noted in RH30 and lesser in Alankar. Cd treatment decreased the seed yield by 32.47% in Alankar and 52.68% in RH30 in comparison with the control (Table 1). The yield parameters such as number of seeds per siliqua, number of siliqua per pant and 1,000 seed weight were decreased by 33.79%, 35.70% and 41.44% in Alankar and 55.88%, 53.82% and 60% in RH30, respectively, compared with the control under 150 mg Cd kg−1 soil (Table 1). Cd stress affects growth and yield through disturbances in several morpho-physiological processes and nutrient uptake.4,22 Wahid and Ghani31 reported significant reduction in number of pods per plant and seeds per pod, 100-seed weight, seed yield and harvest index of Vigna radiata genotypes as a result of Cd toxicity. Wu et al.32 reported reduction in yield of three cotton genotypes under Cd stress and found that the reduction in yield was proportional to Cd accumulation.
Significant accumulation of Cd was found in the roots and leaves of all the mustard cultivars which showed an increasing trend with the increasing Cd concentration in the soil. For each Cd treatment its concentration was always higher in the roots in comparison to leaves in all the cultivars. Maximum Cd accumulation was noted in the roots and leaves of RH30 and less in Alankar under all the Cd treatments. The Cd content in the root and leaves of RH30 was 354.21 and 137.07 µg g−1 dry weight and 273.1 and 70.74 µg g−1 dry weight, respectively, with 150 mg Cd kg−1 soil (Fig. 2A and B). It has been reported that plant species and cultivars significantly differ in the uptake of Cd and its subsequent translocation from roots into shoots.8,10,19,23,33 Higher Cd accumulation in roots than leaves suggest that Cd transport to the xylem is restricted, therefore less in above ground parts, suggesting that Cd is not readily translocated in the phloem.6,34,35 Furthermore, Cd accumulation in the root and leaf also depends on binding to the extracellular matrix.36 It has also been reported that Cd accumulation by plants grown in soil is directly related to transpiration and thereby to stomatal conductance.19,37 Further, the ability of plants to grow on Cd contaminated soils is generally correlated with the ability of roots to exclude Cd from the plant and/or of plant tissues to chelate Cd as a non-toxic compound or sequester it in a non-vital cellular compartment.6,38 Exposure to heavy metals results in the excessive production of ROS in plants. Unlike Cu and Fe, Cd generates ROS by catalyzing Haber-Weiss or Fenton type reactions.39 The peroxidation of lipids is considered as the most damaging process known to occur in every living organism. Previous studies reported that Cd increase the lipid peroxidation in plants due to excessive ROS generation.4,19,22 Membrane damage is sometimes taken as a single parameter to determine the level of lipid destruction under various stresses. It has been reported that metal ions block the electron flow in PS II, which results in the formation of excited Chl causing the production of free oxyradicals.12 In the present study, Cd-induced lipid peroxidation was observed in all the cultivars with increasing Cd concentration in the soil (Fig. 3A) and was highest with 150 mg Cd kg−1 soil. The production of lipid peroxides was lower in Alankar compared to RH30 at all Cd levels. The increase of about 319.60% in TBARS content was observed in Alankar with 150 mg Cd kg−1 soil in comparison to control, whereas in RH30, a higher increase of 412.43% was noted (Fig. 3A). Similarly, H2O2 content was also found to be increased under Cd stress in all the cultivars and it was also high in RH30 than Alankar. The increase of about 142.57% in H2O2 content was observed in Alankar, whereas in RH30, a higher increase of 202.72% was noted with 150 mg Cd kg−1 soil in comparison to their respective control (Fig. 3B). In Alankar the generation of H2O2 was quenched by the efficient antioxidative mechanism, whereas, greater increase in RH30 is indicative of higher oxidative stress imposed by Cd in soil. Previous studies also reported increase in TBARS and H2O2 content in Arabidopsis thaliana;40 Triticum aestivum;22 Pisum sativum;23 Oryza sativa;41,42 Brassica juncea;19 Brassica napus;43 and Vigna mungo;44 under Cd stress. Possible explanation of less TBARS and H2O2 content in Alankar is the fast removal of ROS by antioxidant than in RH30. To protect them against Cd-induced oxidative damage, plant cells and its organelles like chloroplast, mitochondria and peroxisomes employ antioxidant defense systems. The enzymatic antioxidant system involves the sequential and simultaneous action of a number of enzymes including SOD, CAT, APX and GR for the removal of ROS. A great deal of research has established that the induction of the cellular antioxidant machinery is important for protection against Cd stress.4,12,19,22 In the present investigation, significant increase in SOD, CAT and APX activity was noted in all the cultivars exposed to Cd stress. The SOD activity was higher in RH30 in comparison to Alankar at all Cd concentrations. The activity of SOD increased by 116.13% in RH30 and 72.22% in Alankar with 150 mg Cd kg−1 soil compared to their control (Fig. 3C). On the other hand, the CAT, APX and GR activity was higher in Alankar than RH30. GR activity was found to be reduced in RH30 at 150 mg Cd kg−1 soil and it was reduced by 7.69% in comparison to control, whereas in Alankar a 40.62% increase in GR activity was noted (Fig. 3F). The increase of about 54.16% in CAT activity and 128.44% in APX activity was observed in Alankar, whereas in RH30, a lesser increase of 13.97% in CAT activity and 76.36% in APX activity were noted with 150 mg Cd kg−1 soil in comparison to their respective control (Fig. 3D and E). The cultivar Alankar showed lesser increase in SOD activity than RH30, but the activity of CAT, APX and GR were found to be higher in Alankar than RH30. The lesser increase in SOD activity in Alankar can be related with less accumulation of Cd in the leaf of Alankar. The higher SOD activity in RH30 resulted in a greater level of H2O2, and therefore caused higher cellular damage in RH30 than Alankar. Gossett et al.45 reported that higher SOD activity without complementary increase in the ability to scavenge the formed H2O2 can result in the increased cellular damage. Further, higher increase of CAT, APX and GR activity in Alankar resulted in efficient scavenging of Cd-induced ROS than RH30, where the activity of these enzymes was either less or reduced in comparison to the control. Interestingly, the increased activity of GR in Alankar protected the plants from ROS by maintaining the high ratio of GSH/GSSG, which is required for the regeneration of ascorbate and for the activation of several CO2-fixing enzymes.12,15 The increase in GR and APX activity in Alankar suggested the smooth functioning of ascorbate-glutathione cycle, and therefore tolerance to Cd stress than RH30 mustard cultivar. CAT has one of the highest turnover rates for all enzymes: one molecule of CAT can convert ∼6 million molecules of H2O2 to H2O and O2 per minute, whereas APX is involved in scavenging of H2O2 in water-water and ascorbate-glutathione cycles and utilizes ascorbate as the electron donor. Therefore, these enzymes are of utmost importance for the removal of ROS under stressed conditions.12
In conclusion, all the five tested mustard cultivars showed differential tolerance to Cd stress. Cd stress inhibited the growth, photosynthesis and yield but cultivars showed a different degree of tolerance to Cd stress. The Alankar mustard cultivar emerged as tolerant and RH30 as sensitive cultivar. The higher tolerance of Alankar to Cd was due to better coordination between the antioxidative enzymes which help to protect the photosynthetic machinery and thus the yield. Overall, antioxidant machinery also plays an important role in Cd stress tolerance.
Materials and Methods
Plant material and experimental system.
Healthy and authentic seeds of Indian mustard (Brassica juncea L. Czern & Coss) cultivars namely, Alankar, Varuna, Pusa Bold, Sakha and RH30, were obtained from the National Research Centre on Plant Biotechnology (NRCPB) of the Indian Agricultural Research Institute (IARI), New Delhi, India. Seeds were surface sterilized with 0.5% NaOCl and soaked overnight in sterile water at 4°C for uniform germination. The seeds were transferred to 23 cm-diameter earthen pots filled with 5 kg of reconstituted soil19 in the green house under natural day/night conditions (Photosynthetically active radiation >950 mmol m−2 s−1, temperature 23 ± 3°C, relative humidity 75 ± 5%). Cd concentration of 0, 25, 50, 100 or 150 mg Cd kg−1 soil were obtained by adding CdCl2 to the soil. Plants were watered every alternate day with deionized water. Plants were arranged in a randomized complete block design, and each treatment was replicated three times. All the measurements were carried out at 30 days after sowing (DAS).
Measurements of growth and photosynthetic characteristics.
Growth characteristics such as shoot length, root length, leaf area and plant dry weight were measured after 30 days of treatment. Shoot and root length were measured on meter scale. Dry weight was determined after drying the samples in an oven at 80°C till constant weight. Leaf area was measured by a LA211 leaf area meter (Systronics, Hyderabad, India).
Net photosynthetic rate (PN) and stomatal conductance (gs) were recorded in fully expanded leaves using an infrared gas analyzer (IRGA, LiCor, Lincoln, NE) on a sunny day between 10:00 and 11:00. The atmospheric conditions during the measurement were photo synthetically active radiation (PAR), 1,000 ± 5 µmol m−2 s−1, relative humidity 66 ± 5%, atmospheric temperature 25 ± 2°C and atmospheric CO2, 355 µmol mol−1.
Yield characteristics.
At maturity, plants were harvested and the number of seeds per seeds siliqua, number of siliqua per plant, 1,000 seed weight and seed yield were recorded.
Carbonic anhydrase activity.
Carbonic anhydrase activity was measured by adopting the method of Dwivedi and Randhava.46 Leaves, used previously for photosynthesis measurements were used for the enzyme assay. Leaves were cut into small pieces (2–3 mm length) in 10.0 ml 0.2 M cysteine in petri dish at 0–4°C. The solution adhering to the leaf surface was removed with the help of blotting paper followed by the immediate transfer of leaves to test tube having 4.0 ml of 0.2 M Na-phosphate buffer (pH 6.8). To this, 4.0 ml of 0.2 M sodium bicarbonate in 0.02 M sodium hydroxide solution and 0.2 ml 0.002% bromothymol blue indicator were added to the tubes. The tubes were kept at 4°C for 20 min.
CO2 librated during catalytic action of the enzyme on sodium bicarbonate was estimated by titration of the reaction mixture against 0.05 N hydrochloric acid, using methyl red as an indicator. The control reaction mixture was also titrated against 0.05 N hydrochloric acid. The difference of the sample and the control readings was noted for the calculation of the enzyme activity.
Chlorophyll estimation.
Total chlorophyll content was estimated using dimethyl sulfoxide (DMSO) following the method as described by Hiscox and Israelstam.47
Determination of Cd content.
Root and leaf samples were immersed in 5 mM CaCl2 solution for 5 min, rinsed in distilled water, desorbed and blotted for Cd determination.48 Then, the leaf and root samples were dried for 48 h at 80°C, weighed, ground to fine powder and digested with concentrated HNO3 and HClO4 (3:1, v/v). Cd concentration was determined with atomic absorption spectrophotometer (Perkin-Elmer A, Analyst, 300; Norwalk, CT). Tolerance index (TI) for the tested plants was calculated using the formula:
TI (%) = Mean plant dry weight at 150 mg Cd kg−1 soil/Mean plant dry weight at 0 mg Cd kg−1 soil × 100.
Determination of TBARS and H2O2 contents.
The level of lipid peroxidation products in leaves was determined by estimating thiobarbituric acid reactive substances (TBARS) as described by Dhindsa et al.49 Two hundred mg of fresh leaf tissue was ground in 0.25% 2-thiobarbituric acid (TBA) in 10% trichloroacetic acid (TCA) using mortar and pestle. After heating at 95°C for 30 min, the mixture was quickly cooled in an ice bath and centrifuged at 10,000x g for 10 min. The absorbance of the supernatant was read at 532 nm and corrected for non-specific turbidity by subtracting the absorbance of the same at 600 nm. The blank was 0.25% TBA in 10% TCA. The TBARS content was calculated using the extinction coefficient (155 mM−1cm−1).
The H2O2 content was determined according to Okuda et al.50 by grinding leaf samples in ice-cold 200 ml of perchloric acid. After centrifugation at 1,200x g for 10 min, perchloric acid of the supernatant was neutralized with 4 M KOH. The insoluble potassium perchlorate was eliminated by centrifugation at 500x g for 3 min. The reaction was started by the addition of peroxidase and the increase in the absorbance was recorded at 590 nm for 3 min.
Activity assay of superoxide dismutase (SOD), catalase (CAT), ascorbate peroxidase (APX) and glutathione reductase (GR).
Leaf samples were homogenized with an extraction buffer containing 100 mM potassium phosphate buffer (pH 7.0), 0.5% Triton X-100 and 1% polyvinylpyrrolidone (PVP) using pre chilled mortar and pestle. The homogenate was centrifuged at 15,000x g for 20 min at 4°C. The supernatant obtained after centrifugation was used for the enzyme assays. For Ascorbate peroxidase (APX), extraction buffer was supplemented with 2 mM ascorbate. The protein content in the samples was determined using bovine serum albumin (BSA, Sigma-Aldrich) as standard.51
The activity of SOD was assayed by monitoring the inhibition of photochemical reduction of nitro blue tetrazolium (NBT), according to Giannopolitis and Ries.52 The extraction buffer consisted of 50 mM potassium phosphate buffer (pH 7.8) containing 0.1% (w/v) BSA, 0.1% (w/v) ascorbate and 0.05% (w/v) 2-mercaptoethanol. The photoreduction of NBT (production of blue formazan) was measured at 560 nm, and an inhibition curve was made against various volumes of the extract. One unit of SOD was defined as the amount of enzyme required to cause 50% inhibition of the reduction of NBT at 560 nm.
The activity of CAT was determined by the method of Aebi53 with slight modification by monitoring the disappearance of H2O2 at 240 nm. Activity was calculated by using extinction coefficient 0.036 mM−1cm−1. One unit of the enzyme is the amount necessary to decompose 1 mmol of H2O2 per min at 25°C.
The activity of APX was determined according to Nakano and Asada.54 APX activity was calculated by using extinction coefficient 2.8 mM−1cm−1. One unit of the enzyme is the amount necessary to decompose 1 mmol of substrate per min at 25°C.
The activity of GR was determined as described by Foyer and Halliwell55 by monitoring the glutathione-dependent oxidation of NADPH. The activity of GR was calculated by using extinction coefficient 6.2 mM−1cm−1. One unit of enzyme was the amount necessary to decompose 1 mmol of NADPH per min at 25°C.
Statistical analysis.
Data were statistically analysed using analysis of variance (ANOVA) with SPSS (ver. 11; SPSS Inc., Chicago, IL). The results are presented as means ± SE (standard errors). The least significant difference was calculated for the significant data at p < 0.05.
| Cadmium (mg kg−1 soil) | Cultivars | Yield characteristics | |||
|---|---|---|---|---|---|
| Seeds siliqua−1 | Siliqua plant−1 | 1,000 seed weight (g) | Seed yield (g plant−1) | ||
| 0 | Alankar | 13.05 | 86.52 | 5.67 | 6.19 |
| Varuna | 12.6 | 82.46 | 5.55 | 5.76 | |
| Pusa Bold | 10.38 | 75.2 | 4.89 | 4.12 | |
| Sakha | 9.52 | 64.87 | 4.5 | 3.77 | |
| RH30 | 9.0 | 61.38 | 4.25 | 3.17 | |
| 25 | Alankar | 11.67 | 76.54 | 4.89 | 5.34 |
| Varuna | 10.91 | 71.24 | 4.71 | 4.97 | |
| Pusa Bold | 8.44 | 61.52 | 4.01 | 3.39 | |
| Sakha | 7.31 | 50.45 | 3.45 | 2.96 | |
| RH30 | 6.73 | 46.32 | 3.16 | 2.46 | |
| 50 | Alankar | 10.08 | 66.88 | 4.25 | 4.85 |
| Varuna | 9.71 | 62.86 | 4.15 | 4.45 | |
| Pusa Bold | 7.25 | 54.1 | 3.37 | 2.9 | |
| Sakha | 6.12 | 42.71 | 2.89 | 2.56 | |
| RH30 | 5.46 | 39.56 | 2.66 | 2.05 | |
| 100 | Alankar | 8.85 | 60.24 | 3.64 | 4.45 |
| Varuna | 8.38 | 55.67 | 3.53 | 4.01 | |
| Pusa Bold | 6.2 | 48.09 | 2.78 | 2.58 | |
| Sakha | 4.99 | 38.12 | 2.41 | 2.2 | |
| RH30 | 4.4 | 34.68 | 1.99 | 1.73 | |
| 150 | Alankar | 8.64 | 55.63 | 3.32 | 4.18 |
| Varuna | 7.87 | 51.9 | 3.05 | 3.72 | |
| Pusa Bold | 5.78 | 42.75 | 2.48 | 2.36 | |
| Sakha | 4.51 | 31.66 | 1.98 | 1.85 | |
| RH30 | 3.97 | 28.34 | 1.7 | 1.5 | |
| LSD0.05 (C × T)* | 0.31 | 1.83 | 0.12 | 0.14 | |
Values are presented as Mean ± S.E. (n = 3). Significant difference at p < 0.05 was determined by least significant difference (LSD) test to compare the means.
* C, cultivar and T, treatments.
Figures and Tables
an evaluation of the role of antioxidant machinery
Published online:
01 February 2011Figure 1 Effect of different Cd concentrations (0, 25, 50, 100 or 150 mg Cd kg−1 soil) on shoot length (A), root length (B), plant dry weight (C), leaf area (D), net photosynthetic rate (PN) (E), stomatal conductance (gs) (F), carbonic anhydrase (CA ) activity (G) and chlorophyll (Chl) content (H) of five mustard (Brassica juncea L.) cultivars at 30 days after sowing. Values are presented as Mean ± SE. (n = 3). Significant difference at p < 0.05 was determined by least significant difference (LSD) test to compare the means.
![]({"type":"image","src":"/na101/home/literatum/publisher/tandf/journals/content/kpsb20/2011/kpsb20.v006.i02/psb.6.2.15049/20141028/images/medium/kpsb_a_10915049_f0001.gif"})
Figure 1 Effect of different Cd concentrations (0, 25, 50, 100 or 150 mg Cd kg−1 soil) on shoot length (A), root length (B), plant dry weight (C), leaf area (D), net photosynthetic rate (PN) (E), stomatal conductance (gs) (F), carbonic anhydrase (CA ) activity (G) and chlorophyll (Chl) content (H) of five mustard (Brassica juncea L.) cultivars at 30 days after sowing. Values are presented as Mean ± SE. (n = 3). Significant difference at p < 0.05 was determined by least significant difference (LSD) test to compare the means.
an evaluation of the role of antioxidant machinery
Published online:
01 February 2011Figure 2 Effect of different Cd concentrations (0, 25, 50, 100 or 150 mg Cd kg−1 soil) on leaf (A) and root (B) Cd content of five mustard (Brassica juncea L.) cultivars at 30 days after sowing. (C) Tolerance index of five mustard (Brassica juncea L.) cultivars treated with 150 mg Cd kg−1 soil. Tolerance index was calculated as percentage of plant dry weight obtained in 150 mg Cd kg−1 soil and of control. Values are presented as Mean ± SE. (n = 3). Significant difference at p < 0.05 was determined by least significant difference (LSD) test to compare the means.
![]({"type":"image","src":"/na101/home/literatum/publisher/tandf/journals/content/kpsb20/2011/kpsb20.v006.i02/psb.6.2.15049/20141028/images/medium/kpsb_a_10915049_f0002.gif"})
Figure 2 Effect of different Cd concentrations (0, 25, 50, 100 or 150 mg Cd kg−1 soil) on leaf (A) and root (B) Cd content of five mustard (Brassica juncea L.) cultivars at 30 days after sowing. (C) Tolerance index of five mustard (Brassica juncea L.) cultivars treated with 150 mg Cd kg−1 soil. Tolerance index was calculated as percentage of plant dry weight obtained in 150 mg Cd kg−1 soil and of control. Values are presented as Mean ± SE. (n = 3). Significant difference at p < 0.05 was determined by least significant difference (LSD) test to compare the means.
an evaluation of the role of antioxidant machinery
Published online:
01 February 2011Figure 3 Effect of different Cd concentrations (0, 25, 50, 100 or 150 mg Cd kg−1 soil) on thiobarbituric acid reactive substances (TBARS) content (A), hydrogen peroxide (H2O2) content (B), superoxide dismutase (SOD) activity (C), catalase (CAT) activity (D), ascorbate peroxidase (APX) activity (E) and glutathione reductase (GR) activity (F) of five mustard (Brassica juncea L.) cultivars at 30 days after sowing. Values are presented as Mean ± SE. (n = 3). Significant difference at p < 0.05 was determined by least significant difference (LSD) test to compare the means.
![]({"type":"image","src":"/na101/home/literatum/publisher/tandf/journals/content/kpsb20/2011/kpsb20.v006.i02/psb.6.2.15049/20141028/images/medium/kpsb_a_10915049_f0003.gif"})
Figure 3 Effect of different Cd concentrations (0, 25, 50, 100 or 150 mg Cd kg−1 soil) on thiobarbituric acid reactive substances (TBARS) content (A), hydrogen peroxide (H2O2) content (B), superoxide dismutase (SOD) activity (C), catalase (CAT) activity (D), ascorbate peroxidase (APX) activity (E) and glutathione reductase (GR) activity (F) of five mustard (Brassica juncea L.) cultivars at 30 days after sowing. Values are presented as Mean ± SE. (n = 3). Significant difference at p < 0.05 was determined by least significant difference (LSD) test to compare the means.
Table 1 Effect of different Cd concentrations (0, 25, 50, 100 or 150 mg Cd kg−1 soil) on yield characteristics like number of seeds siliqua−1, number of siliqua plant−1, 1,000 seed weight and seed yield of five mustard (Brassica juncea L.) cultivars at 120 days after sowing
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