Differential responses in the photosynthetic efficiency of Oryza sativa and Zea mays on exposure to Cd and Zn toxicity

Alterations in the photochemical responses of Zea mays L. and Oryza sativa L. were analyzed to compare the tolerance level of these two crops towards Cd and Zn toxicity. To achieve this, photosynthetic efficiency of maize and rice plants was probed on the 8 days of CdCl2 and ZnSO4 exposure using chlorophyll a fluorescence kinetics, a noninvasive method suitable to examine the impact of different toxic compounds on photochemistrys. Analysis of induction curves and phenomenological energy pipeline models showed that both Cd and Zn reduced the efficiency of electron transport and associated photosystem II (PSII) functionality. A strong negative correlation was found between the accumulation of reactive oxygen species and ascorbate with the photosynthetic efficiency in both crops, but rice was more tolerant than maize towards Cd and Zn toxicity. Further, we found that Cd strongly affected the early photochemical reactions of maize, which can be considered as the reason for the higher vulnerability of this crop towards Cd. Our study suggests that the non-specific toxic effects of Cd and Zn resulted in chlorophyll degradation, reduction in efficiency of PSII and the disturbance in the electron transport process.

Automated summary

This study compared the tolerance level of maize and rice towards Cd and Zn toxicity, with rice showing higher tolerance. The toxic effects of Cd and Zn included chlorophyll degradation, reduction in PSII efficiency, and disturbance in the electron transport process.