Assessment of photochemical performance of photosystem II in Limbarda crithmoides and Helianthus annuus under Pb stress using chlorophyll a fluorescence kinetics

In the present work, the effectiveness of chlorophyll a fluorescence as a quick tool to detect the effect of Pb–stress on Limbarda crithmoides and Helianthus annuus species, when exposed to increasing Pb concentrations (0–500 µmol.L–1) for 45 days, was evaluated. The chlorophyll level in plant leaves, as well as the fresh weight and Pb content in the shoots and roots in both plant species, were also determined. L. crithmoides did not show any significant variation in photochemical quenching parameters and energy fluxes in all Pb concentrations despite the change in OJIP plot of 100 µmol.L–1 Pb. In addition, a significant increase in chlorophyll a content was noted along with an increase in the biomass production. However, in H. annuus, Pb stress increased energy absorption, dissipation and trapping and decreased energy transport and electron transport rate. In addition, the OJIP curve showed a notable modification at 300 and 500 µmol.L–1 Pb, without significant changes in the chlorophyll contents and in the biomass production under all Pb concentrations. Results also revealed that Pb was accumulated in the shoots and roots of L. crithmoides and H. annuus and the accumulation was more notorious in the roots of the treated plants. Lead exhibited different influence on the photosystem II performance in both species, thus, the evaluation of chlorophyll fluorescence was a very efficacious tool to reflect the physiological status of L. crithmoides and H. annuus under Pb stress.