Biosafety assessment of graphene nanosheets on leaf ultrastructure, physiological and yield traits of Capsicum annuum L. and Solanum melongena L.

Abstract

Due to limited knowledge of graphene nanosheets (GNS) on phyto-biological studies, GNS was sprayed to pepper and eggplants during the seasons 2016 and 2017 at doses 0.1, 0.2 and 0.3 GNS g L−1 to assess their biosafety on leaf ultrastructure and agro-physiological traits. GNS was localized on plastids, cell walls and intercellular spaces of both plants. GNS-sprayed peppers characterized by giant chloroplasts with large starch granules and increment of mitochondrial number adjacent to chloroplasts. Whilst, chloroplast ultrastructure of GNS-treated eggplants appeared to be ellipsoidal-shaped with few normal sized-starch granules compared to control. The localization of GNS inside chloroplast may be activated photosynthetic pigments; thereby stimulation of fructose, sucrose and starch was displayed. The rising of hydrogen peroxide of GNS-treated leaves had beneficial role on triggering the activity of catalase, ascorbate peroxidase, glutathione peroxidase and glutathione-S-transferase. Furthermore, the reduction of hydroxyl radical and superoxide anion reflected the involvement of GNS in induction of antioxidant molecules and superoxide dismutase for modulating cell oxidative status. Thus, the lipid peroxidation and electrolyte leakage of GNS-treated plants were kept below the baseline of water-sprayed plants. Moreover, the promotions of health-promoting secondary metabolites via GNS aerosol were in close association to exacerbation of phenylalanine ammonialyase actvity. This study conclusively demonstrated that GNS did not have cytotoxic properties in pepper and eggplant cells rather healthy growth and promoted yield in the terms of number of branches plant−1, number of fruits plant−1 and fruit yield (ton hectare−1) were the net result of GNS-induced metabolic regulation of the leaves physiological status.