Ecophysiology of plants under cadmium toxicity: Photosynthetic and physiological responses

Abstract

Cadmium (Cd) is among the elements that exhibit a pronounced toxic effect on a variety of physiological and metabolic processes. Photosynthesis is one of the main processes of autotrophic organisms. The negative effect of cadmium on the photosynthetic apparatus leads to inhibition of many metabolic pathways that ensure the vital activity of plants. Cadmium can have a direct effect on photosystem II, decreasing the electron transfer rate and inhibiting the oxygen-generatingcomplex. Besides that, under the cadmium influence, there is a violation of the structure and synthesis of pigments, a quantity reduction in open reaction center (RC), as well as inhibition of enzymes in the dark phase of photosynthesis. In addition, Cd can indirectly affect photosynthesis as a result of changes in plant water metabolism, stomata closure, and reduction in CO2 availability for assimilation centers. Under oxidative stress caused by cadmium, the integrity of thylakoid membranes is impaired, as well as the rate of photosynthesis decreases as a result of inhibition of the activity of CO2 fixation enzymes. At the level of the whole plant, disruption of the photosynthesis process is accompanied by a decrease in the growth rate and productivity of plants. The review discusses the toxic effects of cadmium both directly on photosynthesis and on other processes associated with it.