Zinc Affects Differently Growth, Photosynthesis, Antioxidant Enzyme Activities and Phytochelatin Synthase Expression of Four Marine Diatoms

Abstract

Zinc-supplementation (20 μM) effects on growth, photosynthesis, antioxidant enzyme activities (superoxide dismutase, ascorbate peroxidase, catalase), and the expression of phytochelatin synthase gene were investigated in four marine diatoms (Amphora acutiuscula,Nitzschia palea,Amphora coffeaeformisandEntomoneis paludosa). Zn-supplementation reduced the maximum cell density. A linear relationship was found between the evolution of gross photosynthesis and total chlorophyll content. The Zn treatment decreased the electron transport rate except inA. coffeaeformisand inE. paludosaat high irradiance. A linear relationship was found between the efficiency of light to evolve oxygen and the size of the light-harvesting antenna. The external carbonic anhydrase activity was stimulated in Zn-supplementedE. paludosabut was not correlated with an increase of photosynthesis. The total activity of the antioxidant enzymes did not display any clear increase except in ascorbate peroxidase activity inN. palea. The phytochelatin synthase gene was identified in the four diatoms, but its expression was only revealed inN. palea, without a clear difference between control and Zn-supplemented cells. Among the four species,A. paludosawas the most sensitive andA. coffeaeformis, the most tolerant.A. acutiusculaseemed to be under metal starvation, whereas, to survive, onlyN. paleadeveloped several stress responses.