Effect of GeO 2 on embryo development and photosynthesis in Fucus vesiculosus (Phaeophyceae)

Abstract

Germanium dioxide (GeO2 ) has been used for many years in the cultivation of red and green algae as a means of controlling the growth of diatoms. Brown algae are sensitive to GeO2 , however, the basis of this sensitivity has not been characterized. Here we use embryos of Fucus vesiculosus to investigate morphological and physiological impacts of GeO2 toxicity. Morphometric features of embryos were measured microscopically, and physiological features were determined using pulse amplitude modulated (PAM) fluorometry. At 5 mg L-1 GeO2 , embryos grew slower than controls and devel- oped growth abnormalities. After 24 h, initial zygote divisions were often oblique rather than transverse. Rhizoids had inflated tips in GeO2 and were less branched, and apical hairs were deformed, with irregularly aligned, spheroidal cells. Minimum fluorescence (F0 ) showed minor differences over the 10 days experiment, and pigment levels (chlorophylls a, c and total carotenoids) showed no difference after 10 days. Optimum quantum yield increased from ca. 0.52 at 24 h to 0.67 at 5 days, and GeO2 -treated embryos had higher mean values (significant at 3 and 5 days). Optimum quantum yield of photosystem II (ΦPSII ) was stable in control thalli after 5 days, but declined significantly in GeO2 . Addition of silica (as SiO2 ) did not reverse the effects of GeO2 . These results suggest that GeO2 toxicity in brown algae is associated with nega- tive impacts at the cytological level rather than metabolic impacts associated with photosynthesis.