Comparative Physiological and Transcriptomic Analyses Reveal the Toxic Effects of ZnO Nanoparticles on Plant Growth

Zinc
oxide (ZnO) nanoparticles (nZnO) are among the most commonly
used nanoparticles (NPs), and they have been shown to have harmful
effects on plants. However, the molecular mechanisms underlying nZnO
tolerance and root sensing of NP stresses have not been elucidated.
Here, we compared the differential toxic effects of nZnO and Zn2+ toxicity on plants during exposure and recovery using a
combination of transcriptomic and physiological analyses. Although
both nZnO and Zn2+ inhibited primary root (PR) growth,
nZnO had a stronger inhibitory effect on the growth of elongation
zones, whereas Zn2+ toxicity had a stronger toxic effect
on meristem cells. Timely recovery from stresses is critical for plant
survival. Despite the stronger inhibitory effect of nZnO on PR growth,
nZnO-exposed plants recovered from stress more rapidly than Zn2+-exposed plants upon transfer to normal conditions, and transcriptome
data supported these results. In contrast to Zn2+ toxicity,
nZnO induced endocytosis and caused microfilament rearrangement in
the epidermal cells of elongation zones, thereby repressing PR growth.
nZnO also repressed PR growth by disrupting cell wall organization
and structure through both physical interactions and transcriptional
regulation. The present study provides new insight into the comprehensive
understanding and re-evaluation of NP toxicity in plants.

氧化锌（ZnO）纳米颗粒（nZnO）是当前应用最为广泛的纳米颗粒（NPs）之一，已有研究证实其对植物具有有害作用。然而，nZnO胁迫下植物的耐受机制以及根系对纳米颗粒胁迫的感知分子机制尚未阐明。本研究结合转录组学与生理学分析手段，对比了nZnO与锌离子（Zn²+）胁迫在暴露期及恢复阶段对植物产生的差异化毒性效应。尽管nZnO与Zn²+均会抑制植物主根（primary root, PR）生长，但nZnO对伸长区生长的抑制作用更强，而Zn²+胁迫则对分生组织细胞具有更强的毒性效应。及时从胁迫中恢复对植物存活至关重要。尽管nZnO对主根生长的抑制作用更强，但经nZnO处理的植物在转移至正常培养条件后，其胁迫恢复速度较Zn²+处理组更快，转录组数据也验证了这一结果。与Zn²+胁迫不同，nZnO可诱导伸长区表皮细胞发生内吞作用，并引发微丝重排，进而抑制主根生长。此外，nZnO还可通过物理相互作用与转录调控双重途径，破坏细胞壁的组织与结构，从而抑制主根生长。本研究为全面理解与重新评估植物体内纳米颗粒毒性提供了全新的视角。