Ultrastructural and Physiological Responses Induced by Nickel and Ozone Stress in Rice (Oryza sativa) Cultivars

Two cultivars of rice (Sakha101 and Giza178) were grown in open-top chambers under O-3 (75 ppb/h) and/or treated with different concentrations of nickel sulphate (0, 10, 50 and 100 mu M). The damaging effect of both stresses was more pronounced and manifested certain differences between the two varieties. Exposure of tolerant and sensitive cultivars to Ni+2 or fumigation with O-3 reduced shoots and roots dry weights, leaf relative water content, chlorophyll fluorescence and mineral content. Contrary, a significant accumulation of total phenolics, flavonoids and phenylalanine ammonia lyase (PAL) activity together with quercetin, catechin and gallic acid were recorded. Based on leaves scanning and transmission electron microscope, both stresses separately had negative effects on stomatal response, epicuticular waxy hairs and papillae. The effect of Ni+2 and O-3 on leaf ultrastructure was observed most conspicuously in the chloroplasts, which revealed alterations in shape and the construction of the thylakoid membranes. Anatomical study of roots displayed variations and disintegration of the exodermis, endodermis, cortex and vascular cylinder. SDS-PAGE protein profile of shoots from the two cultivars revealed qualitative and quantitative changes. Taken together, the interaction between Ni+2 and O-3 were, antagonistic on physiological, ultrastuctural alterations and up-down regulated proteins to counteract the negative effects of both pollutants. (C) 2020 Friends Science Publishers