Abstract
Copper (Cu) is an essential element involved in various metabolic processes in plants, but at concentrations above the threshold level, it becomes a potential stress factor. The effects of two different cytokinins, kinetin (KIN) and 6-benzylaminopurine (BAP), on chlorophyll a fluorescence parameters, stomatal responses and antioxidation mechanisms in castor (Ricinus communis L.) under Cu2+ toxicity was investigated. Ricinus communis plants were exposed to 80 and 160 μM CuSO4 added to the growth medium. Foliar spraying of 15 μM KIN and BAP was carried out on these seedlings. The application of these cytokinins enhanced the tissue water status, chlorophyll contents, stomatal opening and photosynthetic efficiency in the castor plants subjected to Cu2+ stress. The fluorescence parameters, such as Fm, Fv/Fo, Sm, photochemical and non-photochemical quantum yields, energy absorbed, energy trapped and electron transport per cross-sections, were more efficiently modulated by BAP application than KIN under Cu2+ toxicity. There was also effective alleviation of reactive oxygen species by enzymatic and non-enzymatic antioxidation systems, reducing the membrane lipid peroxidation, which brought about a relative enhancement in the membrane stability index. Of the various treatments, 80 µM CuSO4 + BAP recorded the highest increase in photosynthetic efficiency compared to other cytokinin treatments. Therefore, it can be concluded that BAP could effectively alleviate the detrimental effects of Cu2+toxicity in cotyledonary leaves of R. communis by effectively modulating stomatal responses and antioxidation mechanisms, thereby enhancing the photosynthetic apparatus’ functioning.
Highlights
IntroductionThe environmental pollutants released by anthropogenic activities are threatening the existence of biological systems
The results indicated that the exogenous application of cytokinins ameliorated the negative effect of Cu on the photosynthetic pigment composition, which was evidenced by the increased level of chlorophyll and carotenoid contents in the cotyledonary leaves subjected to Cu stress along with cytokinins as compared to those subjected to Cu stress alone
The results of the present study revealed that the Cu stress-mediated negative effect on photosynthetic efficiency in cotyledonary leaves of R. communis was effectively alleviated by the exogenous application of cytokinins
Summary
The environmental pollutants released by anthropogenic activities are threatening the existence of biological systems. Heavy metals are a serious environmental threat which affects the physiology and metabolism of plants [1]. Heavy metals such as cadmium (Cd), chromium (Cr), copper (Cu), iron (Fe), lead (Pb), nickel (Ni), and zinc (Zn) are common pollutants. The distribution of these metals is influenced by industrial effluents, mining, smelting, and various agricultural activities [2]. At concentrations above the threshold level in the growing medium, Cu becomes extremely toxic and causes damages to the DNA, alterations in cell membrane integrity, and interferes in enzyme activity [3]
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