The Molecular Mechanism Of The Enhanced Maize And Rice Growth During Germination By Carbon Nanotubes

Although a large amount of work has been done on biological effects, it still necessitates further study for its complexity, particularly on the gene and epigenetic levels. Research on mechanism of interaction between nanoparticles and plants is essential for assessment and regulation of nano-tech application. In this paper, we used maize (Zea mays L.) and rice (Oryza sativa L.) as materials and investigated the molecular genetic and epigenetic mechanism of the process that plants were exposed to carbon nanotubes. The results are as follows:1. Single-wall carbon nonotubes (SWCNTs) accelerate maize seminal roots growth, but display little effect on the primary root growth. In contrast, root hair growth inhibition by SWCNTs is observed. Further gene transcription analysis shows that SWCNTs could increase the expression of seminal root associated genes whereas decrease root hair associated gene expression. Their effect is on both tissue and gene selectiveness since both enhanced and inhibited gene expression and tissue growth are observed during root development. Microscopy images reveal the distribution of SWCNTs inside the root and mainly in the intercellular space in cortex tissues. We also find that SWCNT-treatment dynamically and selectively induces the up-regulation of epigenetic modification enzyme genes, leading to global deacetylation of histone H3, similar to the response of plants to other stress. The nanoparticle-root cell interaction could cause the change in gene expression, and consequently affect relative root growth and development.2. The results showed that SWCNTs were located in the intercellular space while multi-wall carbon nanotubes (MWCNTs) penetrated cell walls. These two kinds of CNTs could promote rice root growth through the regulation of expression of the root growth related genes and induced the elevated global histone acetylation in rice root meristem zones. These responses were returned to normal levels after CNTs were removed from medium. CNTs caused the similar histone acetylation and methylation statuses across the local promoter region of the CRL1gene and increased this region chromatin accessibility to micrococcal nuclease, which enhanced this gene expression. Our results suggested that the nanoparticles could cause plant responses at the cellular, genetic and epigenetic levels and these responses were independent on interaction modes between root cells and CNTs.3. Both SWCNTs and MWCNTs accelerate rice leaf growth only rice roots exposed in CNTs. Chlorophyll content increased, chloroplast development promoted and photosynthesis rate up-regulated after CNTs treatment. Microscopy images reveal the different chloroplast structures and conditions. Further gene transcription analysis shows that CNTs dynamically increased the expression of plant growth and chloroplast development associated genes. ROS level of rice roots increase, while the SOD, CAT activities of aboveground parts is up-regulated. SWCNTs and MWCNTs in a low concentration induce stimulation of rice growth.