Physiological, Chemical and Metabolite Profiling of Pectobacterium carotovorum-Inoculated Tomato Plants Grown in Nutrient-Amended Soils

Abstract

This study evaluated the effects of a plant pathogenic bacterium Pectobacterium carotovorum strain BD163 inoculation and nutrient solution (CaCO₃ (2 mM), NaCl (1 mM) and K₂Cr₂O₇ (0.001 mM)) on the growth, photosynthesis, nutrient uptake and metabolomics of tomato seedlings. The experiment had four experimental treatments (1. solution + BD163 inoculation, 2. solution alone, 3. BD163 inoculation, 4. control). Plant growth and photosynthesis responses were minimal, and differences in nutrient assimilation and metabolite profiles were clear-cut. Of the photosynthesis parameters, only water use efficiency was impacted; it was higher in the bacterium-only treatment and unchanged in the other treatments. The quantities of boron, bismuth and nickel were affected, accumulating mostly in the "solution + BD163 inoculation" experimental set. Principal component analysis of metabolomics data separated the treatments into three groupings; group 1 was the double treatment, group 2 was the nutrient solution treatment and, finally, group 3 was the P. carotovorum and control treatments. Correlation analysis of the data showed an assumed interdependence of several plant factors. The authors concluded that the interaction between the bacterium, the plant and the nutrient solution is complex and more pronounced at the chemical and metabolite level than at the growth and photosynthesis level.

Keywords: Pectobacterium carotovorum; correlation analysis; metabolomics; nutrient assimilation analysis; photosynthesis; tomato.

Figure 1

Timeline of the experiment. Tomato seedlings were inoculated with Pectobacterium carotovorum and were also treated with a mixture of elements and a nutrient solution (solution), which was CaCO₃ (2 mM), NaCl (1 mM) and K₂Cr₂O₇ (0.001 mM). Gas exchange (GE) measurements were taken on day 6, plant height and stem diameters were measured on day 27 and leaves were sampled on day 27.

Figure 2

Roots and fruit of tomato inoculated with Pectobacterium carotovorum (strain BD163) and treated with a nutrient solution containing CaCO₃ (2 mM), NaCl (1 mM) and K₂Cr₂O₇ (0.001 mM) (column 1); only the nutrient solution (column 2); only BD163 (column 3); and the untreated control (column 4).

Figure 3

(A–C) Combined correlation network of the growth, gas exchange and elemental quantities of tomato seedlings from all experimental treatments, inoculated or not inoculated with Pectobacterium carotovorum (strain BD163) and treated or not treated with a nutrient solution containing CaCO₃ (2 mM), NaCl (1 mM) and K₂Cr₂O₇ (0.001 mM). (A) Correlation coefficients greater than or equal to 0.7 but smaller than 0.8 and correlation coefficients less than or equal to −0.7 but greater than −0.8. (B) Correlation coefficients greater than or equal to 0.8 but smaller than 0.9 and correlation coefficients less than or equal to −0.8 but greater than −0.9. (C) Correlation coefficients greater than or equal to 0.9 but smaller than or equal to 1.0 and correlation coefficients less than or equal to −0.9 but greater than or equal to −1.0.

Figure 4

Computed principal component analysis (PCA) showing separated metabolic features of tomato leaves with four treatments, namely tomato inoculated with Pectobacterium carotovorum (strain BD163) and treated with a nutrient solution containing CaCO₃ (2 mM), NaCl (1 mM) and K₂Cr₂O₇ (0.001 mM) (solution + BD163—red circle), only the nutrient solution (solution—green circle) and only Pc (BD163—blue circle) and the untreated control (control—purple circle). Analysis with the LCMS-9030 qTOF was performed on leaves sampled 27 days after exposure to the treatments.

Figure 5

Computed partial least significant discriminant analysis (PLS-DA) showing separated metabolic features of tomato leaves with four treatments, namely tomato inoculated with Pectobacterium carotovorum (strain BD163) and treated with a nutrient solution containing CaCO₃ (2 mM), NaCl (1 mM) and K₂Cr₂O₇ (0.001 mM) (solution + BD163—red circle), only the nutrient solution (solution—green circle) and only Pc (BD163—blue circle) and the untreated control (control—purple circle). Analysis with the LCMS-9030 qTOF was performed on leaves sampled 27 days after exposure to the treatments.

Figure 6

Computed sparse partial least significant discriminant analysis (SPLS-DA) showing separated metabolic features of tomato leaves with four treatments, namely tomato inoculated with Pectobacterium carotovorum (strain BD163) and treated with a nutrient solution containing CaCO₃ (2 mM), NaCl (1 mM) and K₂Cr₂O₇ (0.001 mM) (solution + BD163—red circle), only the nutrient solution (solution—green circle) and only Pc (BD163—blue circle) and the untreated control (control—purple circle). Analysis with the LCMS-9030 qTOF was performed on leaves sampled 27 days after exposure to the treatments.

Figure 7

Nuclear magnetic resonance (NMR) spectroscopy data results. Computed partial least significant discriminant analysis (PLS-DA) showing separated metabolic features of tomato leaves with four treatments, namely tomato inoculated with Pectobacterium carotovorum (Pc) and treated with a nutrient solution containing CaCO₃ (2 mM), NaCl (1 mM) and K₂Cr₂O₇ (0.001 mM) (1—green square), only the nutrient solution (2—blue square) and only Pc (3—maroon square) and the untreated control (4—yellow square). Analysis with NMR spectroscopy was performed on leaves sampled 27 days after exposure to the treatments. The numbers and the accompanying letters are for the treatment and the plant. For each treatments plants were labelled a, b, c and d. X[1] = 0.602, R2X[2] = 0.16, Ellipse: Hotelling’s T2 (95%).