Cloncurry buffel grass mitigated Cr(III) and Cr(VI) toxicity in tomato plant

Abstract

Contamination of agricultural soil with chromium (Cr) ions has threatened global crop, human and ecosystem health. Its two oxidation states viz. Cr(III) and Cr(VI) are most stable and readily available to the plants. The study explored the impact of increasing exposure (up to 500 ppm) of Cr(III) and Cr(VI) on bio-physical traits of 15-day-old seedlings (in vitro) as well as 60-day-old tomato plant (in vivo), and highlighted the importance of buffel grass (Cenchrus pennisetiformis) in mitigating Cr levels in the tomato plants. In vitro, Petri plate bioassays with 13 different concentrations (20-500 ppm) of Cr(III) and Cr(VI) depicted the highly toxic effect of metal ions ≥ 200 ppm on all bio-physical traits of tomato seedlings. In vivo, soil spiked with Cr(III) and Cr(VI) (200, 300, and 400 mg/kg) was amended with 1% and 2% dry biomass of buffel grass. Phytotoxicity was higher in Cr(VI)-spiked soil compared with Cr(III)-spiked soil. Cr was mainly accumulated in tomato roots, and more Cr was translocated from roots to shoots from Cr(VI)-spiked soil than Cr(III)-spiked soil. Soil amendments with 2% weed biomass reduced metal toxicity in plants, particularly at 200 and 300 mg/kg of Cr. Protein profiles through SDS-PAGE revealed 12-50 kDa (mainly PR proteins) as an important region in tomato leaf, where many new bands were expressed under different treatments, particularly in the treatments provided with buffel grass. PCA-based biplot clearly separated Cr tolerance treatments from highly sensitive treatments. For the cultivation of tomato plants in Cr(III) and Cr(VI) contaminated soil (200 and 300 mg/kg), the biomass of Cloncurry buffel grass should be considered an effective and easily available phyto-management option.

Figure 1

(a–n) Germination, seedling growth, and biomass of tomato due to the effect of 13 different concentrations of Cr(III) and Cr(VI) in Petri plate bioassays. Vertical bars show standard errors of the means of three replicates. Values with different letters at their top show a significant difference (p ≤ 0.05) as determined by the LSD test.

Figure 2

(a and b) Regression analysis for the relationship between tolerance indices (%) of tomato against 13 different concentrations of Cr(III) and Cr(VI) for 15-day-old tomato seedling in Petri plate bioassays.

Figure 3

(a and b) Principal component analysis of germination, growth, and biomass due to the effect of 13 different concentrations of Cr(III) and Cr(VI) in Petri plate bioassays. GR Germination, SL shoot length, RL root length, SFW shoot fresh weight, SDW shoot dry weight, RFW root fresh weight, RDW root dry weight.

Figure 4

(a–l) Effect of soil amendment with plant biomass of Cloncurry buffel grass (CPB) on growth attributes of 60-day old tomato plant under Cr(III) and Cr(VI). Vertical bars show standard errors of the means of three replicates. Values with different letters at their top show a significant difference (p ≤ 0.05) as determined by the LSD test.

Figure 5

SDS-PAGE profile of tomato leaf due to the effect of soil amendment with plant biomass of Cloncurry buffel grass (CPB) under Cr(III) and Cr(VI) stress. The lanes report the MW marker, Molecular Weight protein ladder. T₁: (Without Cr or CPB); T₂: 1% CPB ; T₃: 2% CPB mg/kg; T₄: Cr(III) 200 mg/kg; T₅:1% CPB + Cr(III) 200 mg/kg; T₆: 2% CPB + Cr(III) 200 mg/kg; T₇: Cr(III) 300 mg/kg; T₈: 1% CPB + Cr(III) 300 mg/kg; T₉: 2% CPB + Cr(III) 300 mg/kg; T₁₀: Cr(III) 400 mg/kg; T₁₁: 1% CPB + Cr(III) 400 mg/kg; T₁₂: 2% CPB + Cr(III) 400 mg/kg; T₁₃: Cr(VI) 200 mg/kg; T₁₄: 1% CPB + Cr(VI) 200 mg/kg; T₁₅: 2% CPB + Cr(VI) 200 mg/kg; T₁₆: Cr(VI) 300 mg/kg; T₁₇: 1% CPB + Cr(VI)300 mg/kg; T₁₈: 2%CPB + Cr(VI) 200 mg/kg; T₁₉: Cr(VI) 400 mg/kg; T₂₀: 1% CPB + Cr(VI) 400 mg/kg; T₂₁: 1% CPB + Cr(VI) 400 mg/kg. Full-length gel original image is available as supplementary data files in Fig. S1.

Figure 6

(a and b) Metal uptake by different parts of tomato plant due to soil amendment with plant biomass of Cloncurry buffel grass (CPB) under Cr(III) (a) and Cr(VI) (b) stress. Vertical bars show standard errors of the means of three replicates. Values with different letters at their top show a significant difference (p ≤ 0.05) as determined by the LSD test.

Figure 7

Principal component analysis of biophysical and metal accumulation attributes in 60-day-old tomato plants due to the effect of plant biomass of Cloncurry buffel grass (CPB), Cr(III), and Cr(VI). SL shoot length, RL root length, SFW shoot fresh weight, SDW shoot dry weight, RFW root fresh weight, RDW root dry weight, TF translocation factor, BF bioconcentration factor, Cr chromium accumulation.