Photosynthetic Response of Maize Plants Against Cadmium and Paraquat Impact

The effects of cadmium (Cd) and/or paraquat (PQ) toxicity on photosynthesis in maize leaves were examined by measurement of gas exchange and chlorophyll content in hydroponically cultured plants. It was found that growth rate was distinctly influenced only by 100 A mu M Cd treatment. Chlorophyll a and chlorophyll b decreased along with the increase of Cd concentration, while PQ spraying, alone and combined with Cd, increased chlorophyll a content on the third and seventh experimental days. Generally, carotenoid content increased in response to Cd and PQ and reached the highest levels at 100 A mu M Cd. Rate of photosynthesis in maize decreased after Cd treatment. CO2 assimilation was approximately 60% reduced at 50 A mu M Cd and 70% reduced in the presence of 100 A mu M Cd. PQ toxicity was partly overcome after the third day of exposure. Transpiration and stomatal conductance in maize leaves decreased on the third day along with Cd concentration and PQ spraying, except for the 25-A mu M Cd-treated plants. On the tenth day, the 25-A mu M Cd-treated plants and those from PQ-treated variants showed an increase of transpiration and stomatal conductance. Maize exhibited an ability to accumulate Cd in high quantities, especially in the roots-over 4,500 mg Cd/kg dry weight.