The effect of carbon nanotubes on the seed germination and seedling growth of four vegetable species

Carbon nanotubes (CNTs) can change the morphological and physiological characteristics of plant cells. Laboratory and greenhouse studies were conducted to study the effect of CNTs on the germination and seedling growth of tomato (Lycopersicum esculentum Mill. cv. ‘Falcato’), onion (Allium cepa L. cv. ‘Yellow Sweet Spanish’), turnip (Brassica rapa L. cv. ‘Toria’) and radish (Raphanus sativus L. cv. ‘Small radish’). Seeds were germinated in four concentrations of CNTs (0, 10, 20 and 40 mg L-1) in Petri dishes under laboratory conditions. The same concentrations were used in a greenhouse to study the response of seedling growth to CNTs. To evaluate the effect of CNTs on germination and growth, germination percentage (GP), germination rate (GR), seedling length, seedling fresh and dry weight and mean germination time (MGT) were measured. Scanning electron microscopy (SEM) was used to confirm the presence of CNTs. CNTs at 10–40 mg L-1 improved tomato and onion germination more than for radish and turnip, the highest GP in tomato and onion being 8 and 95%, respectively. In radish, the control showed the highest GP (96%) under laboratory conditions. CNTs at 40 mg L-1 had a deleterious and toxic effect on onion and radish seed germination. In the greenhouse experiment, the fresh weight of radish seedlings decreased as the CNT concentration increased. The dry weight of tomato and radish shoots increased following the application of all concentrations (10–40 mg L-1) of CNTs. CNTs did not alter turnip germination and growth. SEM revealed that the effectiveness of CNTs may depend on the plant species and on the distribution of CNTs on the testa and root surface. CNTs thus provide a viable and important new technique to improve seed germination and selective seedling growth-related characteristics, although the benefit-toxic balance needs to be tested for other horticultural crops and other (higher) concentrations of CNTs.