Mechanism of magnesium oxide nanoparticles effectively stimulate the Mg absorption and growth of tomato plants

Objectives To evaluate the effect of the antibacterial-concentration magnesium oxide nanoparticles (MgONPs) application on growth and transportation efficiency of tomato, which would provide theoretical basis for the application of MgONPs in the field of plant nutrition and disease control.

Methods Taking tomato as the model plant, the tomato seeds and seedlings were treated with different concentrations of MgONPs to measure the seed germination, plant biomass, tissue cell morphology, chlorophyll content and relative water content, as well as the MgONPs-uptake in tomato plant using ICP-OES and TEM.

Results MgONPs had no inhibition on the tomato seeds germination at the concentration of 50–250 μg/mL, and significantly increased the tomato seedling growth, especially at 250 μg/mL treatment. In the 250 μg/mL MgONPs group, the root length, dry root weight and dry weight of aboveground part of tomato and stem girth were 20.33 cm, 0.11 g, 0.20 g and 1.65 cm, respectively, and the corresponding values in the control were 15.63 cm, 0.03 g, 0.15 g and 1.16 cm, respectively. The chlorophyll content and the relative water content of tomato were respectively increased by 47.37% and 13.14%. Furthermore, MgONPs enhanced Mg absorption, and increased the Mg content in leaves by 35.16%; meantime, the aggregation of nanoparticles around chloroplasts in leaves was observed in TEM images. In addition, SEM and paraffin section observation confirmed that MgONPs did not damage tomato plant tissue and cell morphology, further clarified the non-toxic side effects of MgONPs on tomato plant cells.

Conclusions Although the dispersing of MgONPs in soil is not as good as in de-ionized water, it still shows good promotion effect on the germination and seedling growth of tomato significantly, within the tested concentration range of 50–250 μg/mL, without toxicity to plant cells and organ structures. After applied into soil, MgONPs could be absorbed by root and up-transported into leaves through fibrovascular system completely. The increased Mg thus increases chlorophyll content and relative water content of leaves, and stimulates the growth and accumulation of dry biomass of tomato. Under the experimental condition, higher MgONPs concentration performs better than the lower concentration.