Dual Effect of Nanomaterials on Germination and Seedling Growth: Stimulation vs. Phytotoxicity

Abstract

Due to recent active research, a large amount of data has been accumulated regarding the effects of different nanomaterials (mainly metal oxide nanoparticles, carbon nanotubes, chitosan nanoparticles) on different plant species. Most studies have focused on seed germination and early seedling development, presumably due to the simplicity of these experimental systems. Depending mostly on size and concentration, nanomaterials can exert both positive and negative effects on germination and seedling development during normal and stress conditions, thus some research has evaluated the phytotoxic effects of nanomaterials and the physiological and molecular processes behind them, while other works have highlighted the favorable seed priming effects. This review aims to systematize and discuss research data regarding the effect of nanomaterials on germination and seedling growth in order to provide state-of-the-art knowledge about this fast developing research area.

Silver Nanoparticles Effects on In Vitro Germination, Growth, and Biochemical Activity of Tomato, Radish, and Kale Seedlings

“…Different results concerning the influence of silver nanoparticles on seed germination can be associated with (1) plant parameters: species and its sensitivity to AgNPs concentration and seed characteristics (size, thickness of coat) and (2) nanoparticle characteristics: type, size, concentration, surface stabilizer used, etc. During germination, the nanoparticles first have to penetrate the seed coat containing sclerenchyma (sclereids), which acts as a barrier due to its physicochemical integrity [ 17 ]. Seed coat thickness and NPs size are important factors influencing the uptake and penetration of AgNPs inside seeds.…”

“…When the radicle emerges, the developing tissues of the root apex gain contact with NPs, which may enter the rhizodermis via apoplastic transport, endocytosis, or other carriers. Then, NPs flow within the root toward the vascular cylinder via the symplastic pathways and are translocated to other seedling parts [ 17 ]. Tomato shoots obtained from seeds treated with AgNPs at the highest concentration (100 mg·L −1 ) were characterized by the lowest length (3.64 cm), fresh weight (63.34 mg), and dry weight (3.31 mg) ( Table 1 , Figure 3 ).…”

“…At the molecular level, nanoparticles cause the upregulation of the genes involved in cell division and carbon/nitrogen metabolism. The negative effects observed in seedling growth are probably due to chromosomal aberrations and mitotic abnormalities, leading to reduced cell division in the root meristem, hormonal imbalance, ROS overproduction, and an increased level of lipid peroxidation [ 17 ]. On the other hand, it is worth mentioning that AgNPs-treated radish and kale seedlings had higher fresh and dry weights of the shoots compared to the control plants.…”

“…The germination process is the most sensitive stage of higher plant ontogenesis. Various internal and external factors can modulate catabolic and anabolic processes during germination, thus studying the effects of ENMs during this phase seems to be very informative for researchers and agronomists, especially when looking at edible plants [ 1 , 17 ]. The assessment of nanoparticles toxicity on plants usually involves the measurement of germination time and rate, root elongation, shoot, and root biomass or root tip morphology [ 8 ].…”

“…The assessment of nanoparticles toxicity on plants usually involves the measurement of germination time and rate, root elongation, shoot, and root biomass or root tip morphology [ 8 ]. Several experiments have been conducted with the use of different ENMs, e.g., gold, silver, copper, silicon, zinc oxide, titanium oxide nanoparticles, carbon structures (fullerenes, nanotubes, graphene), quantum dots, showing diverse (stimulating or phytotoxic), dose- and species-dependent effects on germination efficiency, as well as further seedling growth and development [ 17 , 18 ]. The application of zinc oxide nanoparticles at a wide range of concentrations from 50 to 1600 mg·L −1 positively affected the germination in Allium cepa L. with no negative effects on the further growth and development of seedlings being observed [ 19 ].…”