Rhodamine B induced alteration in antioxidant enzymes and photosynthetic performance of Eichhornia crassipes

Synthetic dyes are extensively consumed in numerous industrial applications, resulting in the production of a significant amount of toxic effluents. The purpose of this study was to examine how different Rhodamine B (RhB) concentrations affected the biochemical and physiological functions of Eichhornia crassipes . Therefore, we looked into the ROS-scavenging enzyme activities (Such as SOD, CAT, and GPOD), chlorophyll pigment, and Chl a fluorescence transient (OJIP test) during 24 to 120 h of Rhodamine B exposure at different concentrations of dye (50, 100, 150, 200 and 500 mg/L). The antioxidant enzyme showed increased activity with 50 mg/L Rhodamine B application up to 120 h, but at higher dye concentrations (100, 150, 200, and 500 mg/L), it was enhanced initially up to 48 h, then dropped continuously up to 120 h while chlorophyll content decreased as RhB concentration increased in the culture medium. Chlorophyll a fluorescence OJIP kinetics was influenced by the treatment of Rhodamine B. The peak of fluorescence (Fm) gradually dropped and flattened with increasing dye concentration and exposure time length. Treatment of Rhodamine B, increased absorption efficiency (ABS/RC), trapped energy (TR/RC), and dissipation energy fluxes per PSII RC (DI/RC) in all experimental plants while it drastically declined the maximal fluorescence (Fm), a ratio of rate constants for photochemical and non-photochemical use of RC (Fv/Fo), reaction center efficiency, (RC/CSm) absorption efficiency (ABS/CSm) , electron transport potential (ET/CSm), and trapped energy potential (TR/CSm) per cross section when the concentration of RhB (50,100,150,200 and 500 mg/l) and exposure period (24, 48, 72, 96 and 120 h) were increased. With different concentrations and treatment periods of Rhodamine B, minimal fluorescence (Fo), electron transport efficiency per reaction center (ET/RC), and dissipation flux per cross section (DI/CSm) was increased continuously at lower concentration and higher concentration initially increased for a shorter duration after that it decreased when exposure of Rhodamine B was increased. It also decreased the maximal quantum yield of primary photochemistry (ɸPo), the quantum yield of electron transport (ɸEo), and the rate of the trapped exciton (Ψo) while the quantum yield of energy dissipation in PSII antenna (ɸDo) was decreased after increasing exposure time and concentration of Rhodamine B. Overall it decreased performance index on absorption (PI ABS ) and cross section (PI CSm ) basis with increased concentration and time of Rhodamine B. The acceptor and donor sides of the PS II RC were destroyed, and energy passage from the antenna to the reaction center was also obstructed, at high concentrations of Rhodamine B according to studies of chlorophyll a fluorescence emission. Overall, Rhodamine B markedly altered photosynthetic performance and antioxidant system in E. crassipes .