Abstract
Polychlorinated biphenyls (PCBs) are persistent organic pollutants often found in the atmosphere. Phytoremediation of airborne PCBs is an emerging new concept to minimize potential human exposure. However, effects of atmospheric PCBs on plant growth, photosynthesis and antioxidant defence system are poorly understood area. Brassinosteroids have been reported to alleviate different abiotic stresses including organic pollutants-induced stress. Hence, we studied the effects of PCBs and 24-epibrassinolide (EBR) on biomass accumulation, photosynthetic machinery and antioxidant system in tomato plants. PCBs (0.4, 2.0 and 10μg/l) mist spray significantly decreased dry weight, photosynthesis, chlorophyll contents in a dose dependent manner. Both stomatal and non-stomatal factors were involved in PCBs-induced photosynthetic inhibition. Likewise, the maximal photochemical efficiency of PSII (Fv/Fm), the quantum efficiency of PSII photochemistry (ΦPSII) and photochemical quenching coefficient were increasingly decreased by various levels of PCBs, suggesting an induction of photoinhibition. Increased accumulation of H2O2 and O2- accompanied with high lipid peroxidation confirmed occurrence of oxidative stress upon PCBs exposure. Meanwhile, antioxidant enzymes activity was decreased following exposure to PCBs. Foliar application of EBR (100nM) increased biomass, photosynthetic capacity, chlorophyll contents and alleviated photoinhibition by enhancing Fv/Fm, ΦPSII and qP. EBR significantly decreased harmful ROS accumulation and lipid peroxidation through the induction of antioxidant enzymes activity. Our results suggest a protective role of EBR against PCBs stress which may strengthen phytoremediation approaches by enhancing plant tolerance.
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