The role of MoO3NPs on regeneration, growth and development of chrysanthemum cultured in vitro

This study substituted sodium molybdate dehydrate (Na₂MoO₄.2H₂O) in MS medium (Murashige and Skoog 1962) with molybdenum trioxide nanoparticles (MoO₃NPs) to evaluate their impact on the morphogenesis, growth, absorption of metal-mineral elements and the activity of antioxidant enzymes of chrysanthemum. The results indicated that 100% callus formation was observed when 1-month-old leaf explants were cultured on medium supplemented with MoO₃NPs and Na₂MoO₄.2H₂O in basic MS medium, while leaf explants cultured on MS medium without Na₂MoO₄.2H₂O did not induce callus induction. In addition, the treatment with 223.5 µL/L MoO₃NPs resulted in the highest shoot regeneration (33.33%), with 1 shoot per explant, and shoot height (1.14 cm), and fresh weight (1.21 g) compared to those in others and control treatments. Meanwhile, 1-month-old stem node (1 cm) explants cultured on medium supplemented with 149 µL/L MoO₃NPs recorded 100% shoot regeneration and the highest number of shoots larger than 2 cm (5 shoots/stem node), shoot height (3.23 cm) and fresh weight (1.87 g) of the shoot cluster after 30 days of culture. During the regeneration stage, the activity of antioxidant enzymes in 149 µg/L MoO₃NPs treatment was better than the control (+) treatment (except for SOD) and all the other treatments. Similar results were also observed during the shoot multiplication phase, where either the lack or surplus of Mo in the culture medium also caused the decline of SOD, CAT, and APX enzymes activity. Besides, at the concentration of 6.4 µg/L MoO₃NPs in the culture media, nutrients are absorbed more efficiently and rapidly by explants. These findings suggest that substituting ion salt in the culture medium with MoO₃NPs led to enhanced absorption, providing a micro-mineral source for plants to support biosynthesis and essential functions. The chrysanthemum plantlets exhibited enhanced rooting and growth when treated with 149 µg/L MoO₃NPs, particularly during the rooting stage after 15 days of culture.