Effects of high nitrate concentrations on the germination of carpospores of the red seaweed Pyropia acanthophora var. brasiliensis (Rhodophyta, Bangiales)

Pyropia is a genus of algae used in sushi. Nitrate (NO3−) is essential for its growth. Excess NO3− is flushed into seawater, as a result of anthropogenic activities, increasing the potential for higher than normal concentrations which could be harmful to both algae and humans. This study aims to evaluate the effect of NO3− on the morphology, ultrastructure, spore viability, autofluorescence of chloroplasts, and formation of cell wall, during germination of the red seaweed Pyropia acanthophora var. brasiliensis. To accomplish this, carpospores were cultivated at 24°C, 40 μmol photons m−2 s−1 with photoperiod of 12 h and exposed to 0, 25, 50, and 100 mM of NO3− for 2 days. Samples were cultured for another 5 days to measure the length of the germ tube. Concentrations of NO3− did not significantly influence the development, morphology, viability, or ultrastructure of the spores in the first 2 days. The absence of this nutrient did delay the ultrastructural development of the carpospore, decreasing autofluorescence of the chloroplast and delaying the formation of the cell wall and pyrenoid. Over the seven-day experimental period, higher concentrations of NO3− increased the size of the germ tube, indicating that this extra concentration boosted the development of P. acanthophora.