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 la boratory under various light conditions: white light (as reference) or broad band isoquantic red light (600-700 nm, peak transmission: 660 n m) or blue light (400-580 nm, peak transmission: 430 nm). Growth of ap ices was higher under blue light than in other conditions. Morphogenes is of cultivated thalli under white or red light was different from fi eld plants with high growth of primary axis and low level of ramificat ions. Under blue light, morphogenesis of thalli was similar to those h arvested in nature. Net photosynthesis was measured and P vs I curves were established under white light. Maximum net photosynthetic rates a nd initial slope were higher for thalli cultivated under blue light an d lower under white and red light. Pigment composition was similar und er 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 capa city was due to ribulose 1-5 biphosphate carboxylase, whereas red ligh t stimulated activity of phosphoenolpyruvate carboxykinase. In the low irradiance conditions, only thalli cultivated under blue light presen ted morphological and photosynthetic characteristics similar to harves ted plants. Light responses of C. barbata are related to its future cu ltivation and its natural habitat growth strategy.