Comparative study of growth responses, photosynthetic pigment content, and gene expression pattern in tobacco plants treated with ZnO nano and ZnO bulk particles

The production and use of nanoparticles (NPs) have increased dramatically in recent decades, releasing them into the environment. Pollution of soil, water, and air with these substances affects growth and development of all types of living organisms specially the plants because they are immobile and cannot move away from environmental stresses. Among the most commonly used NPs with a great ecological impact are ZnO NPs. In the present work, we studied the effects of different concentrations of ZnO NPs (0, 25, 50, 100, and 200 mg/L) on an important crop plant, Nicotiana tabacum L., which is also a commonly used model organism in the research of abiotic stress, using biochemical, physiological, and molecular approaches and compared them with the effects of bulk ZnO particles. According to the results, the form of particles and their concentration play an important role in response of plants to the treatment conditions. In fact, ZnO NPs had relatively more pronounced impacts than bulk particles on most plant features, and this was dose dependently. It was observed that ZnO NPs in lower concentration (25 mg/L) provoked the plant growth more than bulk particles which was in accordance with higher photosynthetic pigments content observed in this concentration. Furthermore, the expression of photosynthesis-related genes, i.e., CHLΙ , LHCa/b , and RSSU , as well as the amount of IAA and GA phytohormones, was the highest at 25 mg/L NPs. Further studies are required to better understand the exact mechanism of action of these particles including their entrance mode in to the plant cell and cellular localization, their transportation within the whole plant, and the molecular pathways affected by these particles.