Monitoring moderate Cu and Cd toxicity by chlorophyll fluorescence and P700 absorbance in pea leaves

We investigated the effect of moderate Cu2+ and Cd2+ stress by applying chlorophyll (Chl) fluorescence and P-700 absorbance measurements to monitor the photosynthetic electron transport activity of 3-week-old Pisum sativum L. cv. Petit Proven double dagger al plants grown in a modified Hoagland solution containing 50 mu M CuSO4 or 5 mu M CdCl2. Both heavy metals caused a slight inhibition in PSII photochemistry as indicated by the decrease in the effective quantum efficiency of PSII (I broken vertical bar(PSII)), the maximum electron transport capacity (ETRmax), and the maximum quantum yield for electron transport (alpha). PSI photochemistry was also affected by these heavy metals. Cu2+ and Cd2+ decreased the quantum efficiency of PSI (I broken vertical bar(PSI)) as well as the number of electrons in the intersystem chain, and the Cu2+ treatment significantly reduced the number of electrons from stromal donors available for PSI. These results indicate that PSII and PSI photochemistry of pea plants are both sensitive to moderate Cu2+ and Cd2+ stress, which in turn is easily detected and monitored by Chl fluorescence and P-700 absorbance measurements. Therefore, monitoring the photochemistry of pea plants with these noninvasive, yet sensitive techniques offers a promising strategy to study heavy metal toxicity in the environment.