<p class="first" id="d2572500e103">Much efforts have been devoted to clarify the phytotoxicity
of individual contaminants
in plants, such as individual antibiotic and microplastic; however, little is known
about the phytotoxicity of their combined exposure. Here, we investigated the effects
of individual and combined exposure of wheat (Triticum aestivum L.) (Xiaoyan 22) to
oxytetracycline (OTC) and polyethylene (PE) microplastics using physiological and
metabolic profilings. During the seed germination stage, OTC induced phytotoxicity,
as observed through the changes of root elongation, sprout length, fresh weight and
the vitality index, with significant effect at the 50 and 150 mg·L-1 levels; the effect
of PE microplastics depended on the OTC level in the combined exposure groups. During
seedling cultivation, catalase (CAT) and ascorbate peroxidase (APX), as antioxidant
enzyme indices, were sensitive to OTC exposure stress, although OTC was not determined
in leaves. Untargeted metabolomics of wheat leaves revealed OTC concentration-, metabolite
class- and PE-dependent metabolic responses. Dominant metabolites included carboxylic
acids, alcohols, and amines in the control group and all treatment groups. Compared
to only OTC treatment, PE reprogrammed carboxylic acid and alcohol profiles in combined
exposure groups with obvious separation in PLS-DA. Combined exposure induced fewer
metabolites than OTC exposure alone at the 5 and 50 mg·L-1 levels. The shared metabolite
numbers were higher in the OTC groups than in the PE-OTC groups. Pathway enrichment
analysis showed a drift in metabolic pathways between individual and combined exposure
to OTC and PE, which included glyoxylate and dicarboxylate metabolism, amino acid
metabolism and isoquinoline alkaloid biosynthesis. Among metabolites, aromatic acids
and amino acids were more sensitive to combined exposure than individual exposure.
These results contribute to clarifying the underlying mechanisms of phytotoxicity
of individual and combined exposure to OTC and PE.
</p>