Graphene promotes plant root growth by enhancing root respiration

Abstract To explore the effects of graphene on plant root growth and development, 25 mg/L graphene were used to treat the seedling roots of 48 plant species. These results showed that the total root length of the plants was decreased when cultured by hydroponics method. Whereas the total root length of plant species cultured by soil showed different growth effects, among which the ratio of promotion effect was 69.77%, the ratio of inhibition effect was 11.63% and the no-effect ratio was 18.60%. To gain insights into the molecular mechanisms by which graphene presents different growth effects on the root length, we performed RNA-seq for 32 plant roots treated with 25 mg/L graphene. We totally identified 90,259 DEGs in 32 plant species, among which 55,537 were graphene-induced and 34,722 were graphene-repressed. KEGG pathway enrichment analysis indicated that 43 pathways were assigned to these enriched differentially expressed genes in response to the graphene treatment. Top enriched pathways include starch and sucrose metabolism, glycolysis/gluconeogenesis, pyruvate metabolism, the citrate cycle (TCA cycle), phenylpropanoid biosynthesis, glutathione metabolism, endocytosis, peroxisome etc. The gene expressions of these pathway were induced or repressive in plant roots showing promotion or inhibitory effects, respectively. Accumulation of antioxidant enzyme as well as enhanced respiration might lead to the increasing plant root length. In addition, transcriptome and TEM data showed that graphene enters plant root cells by endocytosis. These results uncovered molecular level influences of graphene on plant roots development.