Graphene-Mediated Antioxidant Enzyme Activity and Respiration in Plant Roots

Graphene was used to treat 48 plant species to investigate its effects on plant root growth. Regarding total root length, the results showed an increase in 65% of angiosperms, inhibition in 22% of angiosperms, and no effect on 13% of angiosperms and two gymnosperms. To gain insights into the molecular mechanisms, we performed RNA-seq on the roots of 32 graphene-treated species. Among them, 24 showed a promotion effect, 4 showed an inhibitory effect, and 4 showed no effect. A total of 90,259 differentially expressed genes (DEGs) were identified in 32 plant species, among which 55,537 were induced by graphene and 34,722 were repressed by graphene. These DEGs were enriched in 43 Kyoto Encyclopedia of Genes and Genomes (KEGG) pathways, and the top enriched pathways included starch and sucrose metabolism, glycolysis/gluconeogenesis, pyruvate metabolism, citrate cycle (TCA cycle), phenylpropanoid biosynthesis, glutathione metabolism, endocytosis, peroxisome, etc. For the plant roots showing promotion effects, graphene entered the root cells by endocytosis, increased the activities of antioxidant enzymes, and further induced the gene expression of the above-mentioned pathways, leading to elevated mitochondrial respiration functions, which were compensated for by increasing the root length. In contrast, the repressed expression of genes in these pathways inhibited the plant roots. Reduced antioxidant enzyme activities as well as weakened respiration led to a decrease in root length. The results uncovered the molecular-level effects of graphene on plant root growth.