RED AND BLUE-LIGHT REGULATION OF GROWTH AND PHOTOSYNTHETIC METABOLISMIN 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 conten t and dimensions of intercellular matrix, was higher in thalli grown i n red light, while concentrations of soluble protein and photosyntheti c pigments (chlorophyll, phycocyanin and phycoerythrin in particular), package effect and cell volume were higher in thalli grown in blue li ght. The slower growth rate in blue light was ascribed mainly to low e fficiency of light absorption (high package effect) and low photosynth etic efficiency (in terms of total photosynthetic pigments) due to lit tle overlap of photosystem I and photosystem II pigments in this red a lga in blue light.