GROWTH, PIGMENT SYNTHESIS AND NITROGEN ASSIMILATION IN THE RED ALGA PORPHYRA SP (BANGIALES, RHODOPHYTA) UNDER BLUE AND RED-LIGHT

The effects of long-term cultivation under red (R) and blue (B) light on growth, pigmentation and nitrogen assimilation in the red alga Porp hyra sp, were investigated. The algae were cultivated for three weeks in 3 L enriched seawater containing 500 mu M nitrate as a N-source; in the second week the medium was fully renovated. Thallus expansion, ce ll 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 r eduction but nitrate reductase activity was in general higher in B tha n 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 re newal of the growth medium. The accumulation of biliproteins (phycoery thrin (PE) and phycocyanin (PC)) was clearly higher under B than under R light as occurred with wide-band absorptance (400-760 nm) and the a bsorptance peak ratios PE/Chla and PE/PC. The ratio biliproteins/solub le proteins was not constant during growth. The rapid changes in this ratio seemed to indicate that biliproteins, in addition to photosynthe tic pigments, can act as transient N-storage compartments. Soluble pro tein and amino acid accumulation was mainly promoted by B light. Howev er, structural protein accumulation was higher in R than in B light. A lthough B light promoted the accumulation of photosynthetic pigments, the photosynthetic rate was higher in R than in B light. The photosynt hetic efficiency under white light was also greater in R-grown than in B-grown algae. In summary, two different growth and metabolic pattern s were found depending on the light quality. In R light, higher photos ynthetic efficiency, growth and carbon storage were promoted while in B light, accumulation of organic nitrogen (biliproteins, soluble prote ins, amino acids) was produced without thallus expansion due to a lowe r C assimilation related to nitrogen.