Sweet Basil Growth, Physiological and Ultrastructural Modification, and Oxidative Defense System Under Water Deficit and Silicon Forms Treatment

Abstract

The current investigation aimed to evaluate the role of silicon forms on sweet basil (Ocimum basilicum L.) biomass and essential oil (EO) production, as well as some physiological and ultrastructural modification under different irrigation regimes. Drought significantly decreased plant growth, photosynthetic pigment, ion, relative water content, catalase activity, and EO yield, meanwhile, increased organic and antioxidant solute concentration, EO percentage, peroxidase activity, and oxidative impairment criteria (hydrogen peroxide, lipid peroxidation, and membrane permeability percentage). Concerning EO constituents, linalool and methyl chavicol were the major components that decreased under drought relative to well-watered plants. Exogenous application of silicon forms under well-watered or drought condition may fully or partially compensate to some extent to sweet basil plant development and biochemical attributes (photosynthetic pigment, ion percentage, antioxidant solutes, and organic osmolytes). The maximum EO yield was obtained by 250 mg L−1 sodium metasilicate (Si) under mild drought. Cell organelles exhibited a different degree of malformation and lyse under severe drought; conversely, application of Si forms nullify the abovementioned injuries caused by drought. In conclusion, application of 250 mg L−1 Si improved drought tolerance in sweet basil herb and EO yield by accelerating their antioxidant system, osmoregulation, and maintaining organelles ultrastructure that induced herb growth and EO yield.