RED AND BLUE-LIGHT REGULATION OF GROWTH AND PHOTOSYNTHETIC METABOLISM IN PORPHYRA-UMBILICALIS (BANGIALES, RHODOPHYTA)

Thallus discs 9 mm in diameter of Porphyra umbilicalis were cultivated for 4 weeks in either blue or red light at 50 mumol m-2 s-1 and 12 h light per day. Growth rate, in terms of weight and area, carbon content and dimensions of intercellular matrix, was higher in thalli grown in red light, while concentrations of soluble protein and photosynthetic pigments (chlorophyll, phycocyanin and phycoerythrin in particular), package effect and cell volume were higher in thalli grown in blue light. The slower growth rate in blue light was ascribed mainly to low efficiency of light absorption (high package effect) and low photosynthetic efficiency (in terms of total photosynthetic pigments) due to little overlap of photosystem I and photosystem II pigments in this red alga in blue light.