Meta-topolin and silica nanoparticles induced vigorous carnation plantlet via regulation of antioxidant status and mineral absorption

This study is an attempt to explore the potential of meta-topolin (MT) and silica nanoparticles (SiNPs) in carnation micropropagation - an in vitro vitrification sensitive cut flower. Among MT concentrations (0.5 mg/L - 3.0 mg/L), 1.0 mg/L MT treatment showed a significant increase in shoot height, leaf length, chlorophyll content, dry weight and dry matter index (DM). However, MT concentration > 2.5 mg/L resulted in increased number of shoots and vitrification. Beside different concentrations SiNPs (0.1 mg/L - 3.0 mg/L) were tested in shoot multiplication, chlorophyll content and DM increased; in contrast, the number of shoots, shoot height and other growth indicators all decreased significantly. The results indicated that MT improved shoot multiplication and reduced vitrification, while SiNPs were less suitable for this stage due to limited water absorption of shoots. Interestingly, SiNPs induced compact shoot structure and stimulated root system development, as well as induced densely closed stomata. Furthermore, the presence of SiNPs increased the activities of antioxidant enzymes Catalase (CAT), Superoxide dismutase (SOD) and Ascorbate peroxidase (APX); besides, SiNPs showed negative correlation with Cu, K and Ca uptake but significantly improved Mg, Fe and Si uptake. However, the plantlets derived from SiNPs showed 2.1–2.8-fold decrease in shoot height compared to the control but significantly increased chlorophyll content, DM index, primary root length and diameter as well as lateral root formation. At the highly tested concentrations of 2.0 mg/L - 3.0 mg/L SiNPs, a decrease in growth, uptake of Mg, Fe, Si and explosion of CAT, APX and SOD antioxidant activity was found, which presumably express stress-induced SiNPs. Nevertheless, carnation plantlets derived from SiNPs showed almost complete survival and well growth in greenhouse conditions. These findings suggest that MT and SiNPs can be used to stimulate growth, reduce vitrification, and harden carnation plantlet in practical micropropagation.