The Influence of Cadmium on Fountain Grass Performance Correlates Closely with Metabolite Profiles

Abstract

The relationship between metabolite changes and biological endpoints in response to cadmium (Cd) stress remains unclear. Fountain grass has good Cd enrichment and tolerance abilities and is widely used in agriculture and landscaping. We analyzed the metabolic responses by detecting the metabolites through UPLC-MS and examined the relationships between metabolite changes and the characteristics of morphology and physiology to different Cd stress in fountain grass. Our results showed that under Cd stress, 102 differential metabolites in roots and 48 differential metabolites in leaves were detected, with 20 shared metabolites. Under Cd stress, most of the carbohydrates in leaves and roots decreased, which contributed to the lowered leaf/root length and fresh weight. In comparison, most of the differential amino acids and lipids decreased in the leaves but increased in the roots. Almost all the differential amino acids in the roots were negatively correlated with root length and root fresh weight, while they were positively correlated with malondialdehyde content. However, most of the differential amino acids in the leaves were positively correlated with leaf length and leaf fresh weight but negatively correlated with malondialdehyde content. Metabolic pathway analysis showed that Cd significantly affects seven and eight metabolic pathways in the leaves and roots, respectively, with only purine metabolism co-existing in the roots and leaves. Our study is the first statement on metabolic responses to Cd stress and the relationships between differential metabolites and biological endpoints in fountain grass. The coordination between various metabolic pathways in fountain grass enables plants to adapt to Cd stress. This study provides a comprehensive framework by explaining the metabolic plasticity and Cd tolerance mechanisms of plants.

Keywords: amino acid; biological endpoint; cadmium stress; fountain grass; metabolic profiling; purine metabolism.

Figure 1

Growth characteristics of fountain grass under cadmium (Cd) stress. (A) Length of leaf and root. (B) Fresh weight of leaf and root. (C) Total fresh weight. (D) Root/Leaf ratio. Different characters denote significant differences at p < 0.05 (n = 3). Vertical bars indicate standard error.

Figure 2

The MDA content, soluble protein content, and SOD, POD, and CAT activities of fountain grass under Cd stress. (A) MDA. (B) Soluble protein. (C) SOD. (D) POD. (E) CAT. Different characters denote significant differences at p < 0.05 (n = 3). Vertical bars indicate standard error.

Figure 3

Heatmap clustering of the relative contents of the differential metabolites of fountain grass under Cd stress (n = 3). Each row represents a metabolite, and each column represents a sample. The warmer color indicates a higher content, and the colder color denotes lower content. (A) Leaf. (B) Root.

Figure 4

Relationships between the differential metabolite changes and biological endpoints (BEs) of fountain grass induced by Cd stress (n = 3). (A) Leaf length as the BE. (B) Root length as the BE. (C) Leaf fresh weight as the BE. (D) Root fresh weight as the BE. (E) Leaf MDA content as the BE. (F) Root MDA content as the BE. The red and blue circles represent active and passive coefficients, respectively. The sizes of the circles represent the variable importance projection (VIP) values.

Figure 5

Top 10 metabolic pathways in the leaf or root of fountain grass affected by cadmium stress via pathway analysis from differential metabolites (n = 3). The pathway impact was computed from the pathway topological analysis and represented via the circle size. The p values obtained from pathway enrichment analysis were shown both by the x-axis (−log₁₀) and color. (A) Leaf. (B) Root.

Figure 6

Effects of cadmium stress on the metabolic map of fountain grass (n = 3). The metabolites in blue text were the differential ones. Green or yellow arrows denote metabolites in the leaf or root, respectively. The up or down arrow direction indicates if the metabolite was up-regulated or down-regulated under cadmium stress. The linking arrows among metabolites with full or dotted lines denote the direct or indirect reactions, respectively. (For an interpretation of these references regarding color in this figure legend, please refer to the web version of this article.)