Systemic Stress and Recovery Patterns of Rice Roots in Response to Graphene Oxide Nanosheets

The
interactions between nanomaterials and plants have attracted
increasing attention. However, the systemic stress and recovery patterns
of plants in response to nanomaterials and the connections between
the molecular responses and the phenotypes remain unclear. Herein,
rice was exposed to graphene oxide (GO) nanosheets at 0.01–1.0
mg/L for 7 days under hydroponic exposure, followed by a 7-day post
exposure (GO-free). The significant upregulation (p < 0.05) of phenylalanine metabolism, secondary metabolism, and
heme peroxidase reflected the stress and recovery patterns of rice
roots exposed to GO. GO triggered 27% and more than 50% decreases
in hydraulic conductivity and aquaporin gene expression (PIP1–3
and PIP2–2), respectively. The uptake of GO was mediated by
aquaporin inhibition. Nanomaterial biotransformation reflected the
potential for rice roots to adapt to GO stress. Oxidative stress,
especially the downregulation of class III peroxidase mRNAs, were
suppressed by GO. Lateral root inhibition, primary root growth, and
cell wall synthesis, as forms of resistance to GO stress, were related
to the significant (p < 0.05) downregulation of
salicylic acid and lignin biosynthesis, as well as the upregulation
of jasmonic acid and laccases. The present study helps elucidate the
molecular and phenotypic responses of plants to nanomaterials, which
are closely linked to their environmental risk assessment.