Carbon nanotubes in the holding solution stimulate flower opening and prolong vase life in carnation

Background: Cut flower longevity is often limited by adverse water relations or oxidative stress. The potential of single- and multi-walled carbon nanotubes (SWCNTs and MWCNTs, respectively) on prolonging vase life was addressed. Dose-response curves were obtained by applying five concentrations (0-80 mg L-1) of SWCNTs or MWCNTs either once as a foliar spray or continuously in the holding solution of three carnation cultivars. Next, the optimal concentration of either SWCNTs or MWCNTs was employed to evaluate several parameters critical for vase life. Results: Foliar spray application exerted minor effects on water relations, flower opening and keeping quality. By contrast, including CNTs in the holding solution sustained a positive water balance for a longer period, improved flower opening and prolonged vase life. These effects were similar between SWCNTs and MWCNTs, and were concentration-dependent. The optimal concentration for vase life was higher for MWCNTs as compared to SWCNTs, and for two cultivars as compared to the third one. At optimal concentration, SWCNTs or MWCNTs in the holding solution generally maintained turgidity, and alleviated chlorophyll degradation, electrolyte leakage and lipid peroxidation. These effects were related to increased activation of enzymatic (ascorbate peroxidase, catalase, peroxidase and superoxide dismutase) and non-enzymatic (carotenoids, polyphenols, and flavonoids) antioxidants. Conclusion: CNTs in the holding solution were very effective in stimulating vase life through improved water relations and enhanced antioxidant machinery stimulation.