Growth, pigment synthesis and nitrogen assimilation in the red alga Porphyra sp. (Bangiales, Rhodophyta) under blue and red light
F.L. Figueroa, J. Aguilera, C. Jiménez, J.J. Vergara, M.D. Robles and F.X. Niell

The effects of long-term cultivation under red (R) and blue (B) light on growth, pigmentation and nitrogen assimilation in the red alga Porphyra sp. were investigated. The algae were cultivated for three weeks in 3 L enriched seawater containing 500 µM nitrate as a N-source; in the second week the medium was fully renovated. Thallus expansion, cell division and growth rate were higher under R than B light. Cells in B light were bigger than those in R light but the number of cells per area, intercellular spaces and cell walls were greater in R than in B light. The cell area decreased during the first week coinciding with an increase in the number of cells per area and thallus expansion, but during a low growth rate phase (between days 10 and 14) the cell area increased mainly in B light. Red light transiently promoted nitrate reduction but nitrate reductase activity was in general higher in B than in R light. Chlorophyll a (Chla) accumulation was similar until the second week, but it was higher under B than under R light after the renewal of the growth medium. The accumulation of biliproteins (phycoerythrin (PE) and phycocyanin (PC)) was clearly higher under B than under R light as occurred with wide-band absorptance (400-760 nm) and the absorptance peak ratios PE/Chla and PE/PC. The ratio biliproteins/soluble proteins was not constant during growth. The rapid changes in this ratio seemed to indicate that biliproteins, in addition to photosynthetic pigments, can act as transient N-storage compartments. Soluble protein and amino acid accumulation was mainly promoted by B light. However, structural protein accumulation was higher in R than in B light. Although B light promoted the accumulation of photosynthetic pigments, the photosynthetic rate was higher in R than in B light. The photosynthetic efficiency under white light was also greater in R-grown than in B-grown algae. In summary, two different growth and metabolic patterns were found depending on the light quality. In R light, higher photosynthetic efficiency, growth and carbon storage were promoted while in B light, accumulation of organic nitrogen (biliproteins, soluble proteins, amino acids) was produced without thallus expansion due to a lower C assimilation related to nitrogen.

Keywords: Chlorophyll, growth, long-term cultivation, light quality, nitrate reductase activity, Porphyra sp., photosynthetic efficiency, phycocyanin, phycoerythrin, red and blue light.
Contents of this volume Sci. Mar. 59(Suppl.1) : 9-20 Back PDF
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