Accumulation, morpho-physiological and oxidative stress induction by single and binary treatments of fluoride and low molecular weight phthalates in Spirodela polyrhiza L. Schleiden

Abstract

The present study examined the interactive effects of fluoride and phthalates on their uptake, generation of reactive oxygen species and activation of antioxidative defence responses in Spirodela polyrhiza L. Schleiden. A hydroponic study was conducted in which S. polyrhiza cultured in Hoagland’s nutrient medium, was exposed to fluoride (50 ppm) and different concentrations viz., 75, 150 300 ppm of diethyl phthalate (DEP) and diallyl phthalate (DAP) individually as well as in combination for the time period of 24, 72, 120 and 168\u2009h respectively. A significant decline in fresh weight, dry to fresh weight ratio, total chlorophyll, carotenoid content and increased anthocyanin content was observed. Fluoride and phthalates was found to be readily accumulated by S. polyrhiza in all the exposure periods. Interestingly, when binary treatments were given in nutrient medium, uptake of both fluoride and phthalate was found to be influenced by each other. In combined treatments, DEP stimulated fluoride uptake, while its own uptake was restricted by fluoride. In contrary to this, fluoride stimulated DAP uptake. Moreover, combined stress further caused significant decrement in carbohydrate, protein content and increment in MDA levels, phenolic content and electrolyte leakage. Nevertheless, phthalates showed more pronounced oxidative stress and growth inhibition compared to fluoride. To cope up with the oxidative damage, enhanced level of antioxidant enzymatic activities was observed in S. polyrhiza under both fluoride and phthalate stress as compared to control. Scanning electron microscope imaging of leaf stomata revealed that combined stress of fluoride with phthalates caused distortion in the shape of guard cells. Confocal micrographs confirmed the generation of reactive oxygen species, cell damage, disruption in membrane integrity, and enhanced levels of glutathione in plant cells. This study focussed on ecotoxicological and interactive significance of fluoride led phthalate uptake or vice versa which was also assumed to confer tolerance attributes.