THE EFFECTS OF LIGHT QUALITY ON GROWTH, PHOTOSYNTHESIS AND DEVELOPMENT IN CULTIVATED THALLI OF CYSTOSEIRA-BARBATA C-AG F-AURANTIA (KUTZ) GIACCONE (PHAEOPHYCEAE, FUCALES)

Apical segments of Cystoseira barbata f. aurantia were grown in the laboratory under various light conditions: white light (as reference) or broad band isoquantic red light (600-700 nm, peak transmission: 660 nm) or blue light (400-580 nm, peak transmission: 430 nm). Growth of apices was higher under blue light than in other conditions. Morphogenesis of cultivated thalli under white or red light was different from field plants with high growth of primary axis and low level of ramifications. Under blue light, morphogenesis of thalli was similar to those harvested in nature. Net photosynthesis was measured and P vs I curves were established under white light. Maximum net photosynthetic rates and initial slope were higher for thalli cultivated under blue light and lower under white and red light. Pigment composition was similar under blue and white light, but under red light, concentrations of Chl a and fucoxanthin were reduced. Carboxylase capacities were measured in vitro. Under blue light, more than 80% of the total carboxylation capacity was due to ribulose 1-5 biphosphate carboxylase, whereas red light stimulated activity of phosphoenolpyruvate carboxykinase. In the low irradiance conditions, only thalli cultivated under blue light presented morphological and photosynthetic characteristics similar to harvested plants. Light responses of C. barbata are related to its future cultivation and its natural habitat growth strategy.