Photosynthetic performance in barley - an evaluating tool of cadmium tolerance

Crop-derived food or feed biofortification, potentially enhance human and animal health, yet excessive applications of sewage sludge and manure have led to hazards accumulation of heavy metals, namely Cd, in agricultural soils associated to cropping practices, threatening food safety. Interestingly, barley (Hordeum vulgare L.) can tolerate high Cd concentrations, withstanding its accumulation until the metal reaches the toxic tissue threshold level. Since the photosynthetic performance may be used as a probe for plant tolerance assessment to Cd, this work evaluates barley responses to Cd contamination and correlates toxicity threshold surpass with photosynthetic related parameters. After plant (H. vulgare L., cv. Ribeka) exposure to high Cd contents for 10 days, it was found that root biomass accumulation was inhibited and biomass allocation within the plant was changed, without noticeable effect on total biomass accumulation at the whole plant level. The maximal shoot Cd concentration (41+8 mg Cd kg-1 dry weight) without any visual toxicity symptoms on the shoots, was found at 28 mg Cd kg-1 sand. Reduced leaf gas exchanges, photosynthetic pigments content and electron transport activity were detected for the high Cd treatment of 42 mg Cd kg-1 sand, although thylakoid lipid peroxidation status did not change. The data confirmed barley tolerance to Cd during growth and the concurrent maintenance of the photosynthetic machinery.