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

Abstract

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.

The Effects of Graphene-Family Nanomaterials on Plant Growth: A Review

“…It can be concluded from the above research that GFNs penetrate seed husks and enter germs at the germination stage; GFNs can be absorbed by the root system and transported to above-ground tissues at the seedling growth stage; and GFNs can penetrate cells and enter chloroplasts, where they are eventually degraded into CO 2 and released. In contrast, He et al and Zhang et al did not detect the existence of GFNs in plants with TEM [ 9 , 39 ]. Interestingly, those two studies were conducted in soil, whereas all previous studies that detected GFNs in vivo were conducted using plants raised in growth medium.…”

“…In the seedling growth stage, GFNs have a large impact on plant root growth, which further affects the growth and development of above-ground organs. The growth of root and aerial organs, which ultimately determines plant biomass, was reportedly stimulated by GFNs in Pinus tabuliformis [ 39 ], Aloe vera [ 45 ], elm [ 46 ], maize [ 46 , 47 ], tomato [ 30 , 41 ], cotton [ 42 ], vinca [ 42 ], coriander [ 48 ], garlic [ 48 ], tobacco [ 49 ], and wheat [ 43 , 50 , 51 ] at appropriate concentrations. GFNs also have positive effects on vinca flower number [ 42 ], coriander and garlic flower growth [ 48 ], tobacco callus growth [ 49 ], and watermelon perimeter [ 52 ].…”

“…Similar to most growth-regulating substances, GFNs have concentration-dependent effects on plant growth (whether activating or inhibiting), and therefore an optimal concentration exists for inducing such effects. For example, the optimal concentrations of GO for promoting the growth of Pinus tabuliformis, Aloe vera , and tomato were 25, 50, and 100 mg/L, respectively [ 39 , 41 , 45 ]. Some studies have demonstrated hormetic biological effects of GFNs, meaning that the response is promoted at low GFN concentrations but inhibited at high concentrations.…”

“…This suggests that there may be multiple mechanisms by which GFNs affect plant growth. We have proposed that GO treatment may mimic a weak stress signal, enhancing root growth and the plant’s ability to cope with the external environment [ 39 ].…”

“…In addition, TEM has been used to observe plant ultrastructure, and several such studies have reported a lack of significant changes in cell ultrastructure in response to GFN treatment [ 9 , 43 ]. However, a large number of TEM observations have shown that accumulation of GFNs can lead to destruction of the vacuolar structure and cell membrane, increases in lysosome number, changes in chloroplast shape and the number of starch granules accumulated in chloroplasts, and even serious damage to structures, such as the nucleus [ 25 , 27 , 32 , 39 , 77 ].…”