Effects of Cadmium on Growth, Photosynthetic Pigments, Photosynthetic Performance, Biochemical Parameters and Structure of Chloroplasts in the Agarophyte Gracilaria domingensis (Rhodophyta, Gracilariales)

This paper aimed to evaluate the effects of different concentrations of cadmium on growth rates, photosynthetic pigments, photosynthetic performance, biochemical parameters and structure of chloroplasts in G. domingensis. To accomplish this, apical segments of G. domingensis were cultivated with different concentrations of cadmium, ranging from 100 to 300 μM, over a period of 16 days, and were processed for transmission electron microscopy analysis. The plants exposed to cadmium showed chloroplast alteration, especially degeneration of thylakoids and a decrease in the concentration of photosynthetic pigments, such as chlorophyll a and phycobiliproteins. However, the volume of plastoglobuli increased. As a defense mechanism, the plants treated with cadmium showed an increase in glutathione reductase activity. These results agree with the decreased photosynthetic performance and relative electron transport rate observed after exposure of algae to cadmium. Taken together, these findings strongly indicate that cadmium negatively affects the ultrastructure and metabolism of the agarophyte G. domingensis, thus posing a threat to the economic vitality of this red macroalga.