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The in vivo effect of ultraviolet radiation-B (UVBR) in apical segments of Chondracanthus teedei was examined. Over a period of 7 days, the segments were cultivated and exposed to photosynthetically active radiation (PAR) at 80 μmol photons m(-2) s(-1) and PAR + UVBR at 1.6 W m(-2) for 3 h per day. The samples were processed for electron microscopy and histochemistry; also was analyzed growth rates, mitochondrial activity, protein levels, content of photosynthetic pigments and photosynthetic performance. UVBR elicited increased cell wall thickness and accumulation of plastoglobuli, changes in mitochondrial organization and destruction of chloroplast internal organization. Compared to controls, algae exposed to PAR + UVBR showed a growth rate reduction of 55%. The content of photosynthetic pigments, including chlorophyll a and phycobiliproteins, decreased after exposure to PAR + UVBR. This result agrees with the decreased photosynthetic performance observed after exposing algae to PAR + UVBR. Irradiation also elicited increased activity of the antioxidant enzyme glutathione peroxidase and decreased mitochondrial NADH dehydrogenase activity, which correlated with the decreased protein content in plants exposed to PAR + UVBR. Taken together, these findings strongly indicate that UVBR negatively affects the architecture and metabolism of the carragenophyte C. teedei.

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The in vitro effect of cadmium on apical segments of Hypnea musciformis was examined. Over a period of 7 days, the segments were cultivated with different concentrations of cadmium, ranging from 50 to 300 μM. The samples were processed for microscopic and histochemical analysis of growth rates, content of photosynthetic pigments, and photosynthetic performance. Cadmium treatments increased cell wall thickness and the accumulation of plastoglobuli. Destruction of chloroplast internal organization was observed. Compared to controls, algae exposed to cadmium showed growth rate reduction, depigmentation, and blending in the lateral branches. The content of photosynthetic pigments, including chlorophyll a and phycobiliproteins, decreased after exposure to different concentrations of cadmium. 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 architecture and metabolism of the carragenophyte H. musciformis, thus posing a threat to the economic vitality of this red macroalgae.

The effect of lead and copper on apical segments of Gracilaria domingensis was examined. Over a period of 7 days, the segments were cultivated with concentrations of 5 and 10 ppm under laboratory conditions. The samples were processed for light, confocal, and electron microscopy, as well as histochemistry, to evaluate growth rates, mitochondrial activity, protein levels, chlorophyll a, phycobiliproteins, and carotenoids. After 7 days of exposure to lead and copper, growth rates were slower than control, and biomass loss was observed on copper-treated plants. Ultrastructural damage was primarily observed in the internal organization of chloroplasts and cell wall thickness. X-ray microanalysis detected lead in the cell wall, while copper was detected in both the cytoplasm and cell wall. Moreover, lead and copper exposure led to photodamage of photosynthetic pigments and, consequently, changes in photosynthesis. However, protein content and glutathione reductase activity decreased only in the copper treatments. In both treatments, decreased mitochondrial NADH dehydrogenase activity was observed. Taken together, the present study demonstrates that (1) heavy metals such as lead and copper negatively affect various morphological, physiological, and biochemical processes in G. domingensis and (2) copper is more toxic than lead in G. domingensis.