Effects of graphene on morphology, microstructure and transcriptomic profiling of Pinus tabuliformis Carr. roots

Graphene has shown great potential for improving growth of many plants, but its effect on woody plants remains essentially unstudied. In this work, Pinus tabuliformis Carr. bare-rooted seedlings grown outdoors in pots were irrigated with a graphene solution over a concentration range of 0-50 mg/L for six months. Graphene was found to stimulate root growth, with a maximal effect at 25 mg/L. We then investigated root microstructure and carried out transcript profiling of root materials treated with 0 and 25 mg/L graphene. Graphene treatment resulted in plasma-wall separation and destruction of membrane integrity in root cells. More than 50 thousand of differentially expressed genes (DEGs) were obtained by RNA sequencing, among which 6477 could be annotated using other plant databases. The GO enrichment analysis and KEGG pathway analysis of the annotated DEGs indicated that abiotic stress responses, which resemble salt stress, were induced by graphene treatment in roots, while responses to biotic stimuli were inhibited. Numerous metabolic processes and hormone signal transduction pathways were altered by the treatment. The growth promotion effects of graphene may be mediated by encouraging proline synthesis, and suppression of the expression of the auxin response gene SMALL AUXIN UP-REGULATED RNA 41 (SAUR41), PYL genes which encode ABA receptors, and GSK3 homologs.