Effects of Cu Stress on Root Growth and Proteomics of Vetiver (Vetiveria zizanioides L.)

To understand the adaptation mechanism of vetiver under copper (Cu) stress, the effects of 5 concentrations of Cu (0, 40, 60, 120, and 150 mg/L CuSO₄) on the morphological and physiological responses of vetiver roots were studied. The differential protein expression in vetiver roots treated with Cu-free (CK) and 60 mg/L CuSO₄ was analyzed by 4D label-free quantitative proteomics technology. The results showed that the root length, root volume, and root tip number of vetiver initially increased and then decreased with increasing Cu concentration. The maximum values of root length and root volume appeared at 60 mg/L, which increased by 13.91% and 85.16%, respectively, compared with CK; copper ions (Cu²⁺) and malondialdehyde (MDA) contents increased with increasing Cu concentration and increased by 1626.40% ~ 2197.46% and 3.61% ~ 76.07% compared with CK, respectively; superoxide dismutase (SOD) increased first and then decreased and increased by 126.52% at 60 mg/L compared with CK; soluble protein reduced by 11.76% at 60 mg/L compared with CK (P < 0.05). A total of 1676 differentially expressed proteins were identified in vetiver roots after Cu stress, of which 765 were upregulated and 911 were downregulated. The differentially expressed proteins mainly occur in subcellular structures such as the cytoplasm, nucleus, and tonoplast; are enriched in amino sugar and nucleotide sugar metabolism, phenylpropanoid biosynthesis, cyanoamino acid metabolism, galactose metabolism, steroid biosynthesis, and other pathways; are involved in hydrolase, internal transferases, pyruvate carboxykinase, etc.; and identified the c-terminal domains of cupin, serine carboxypeptidase, peroxidase, and α-l-arabinofuranosidase. The key proteins, including USP, FRK2, HXK3, RFS6, EXPB, OMT2, AS, SODA3, Pod, ZB8, and PRX7, were significantly expressed and are involved in vetiver's regulation of energy metabolism, root morphological growth, and oxidative stress to increase the tolerance of plants to Cu stress. This study further elaborated on the adaptive mechanisms of vetiver under Cu stress and provided a theoretical basis for the ecological restoration of tailings vegetation.