Morphological, physiological and molecular responses of Nitzschia palea under cadmium stress.

The impact of cadmium on the diatom Nitzschia palea (Kützing) W. Smith 1856 was studied by examining the relation between valve deformities and response through biological processes and genetic expression. Cultures of N. palea were exposed to two Cd treatments (C1 = 2.4 ± 0.6 and C2 = 42.6 ± 4.2 µg Cd/L) along with a control (C0 = 0 µg Cd/L) for 28 days. Cadmium bioaccumulation, diatoms growth, photosynthetic efficiencies, valve deformities and genetic expression were investigated during the course of the experiment. Cadmium exposure had significant effects on bioaccumulation, growth, valve deformities and genetic expression. Maximal effects for all studied endpoints were recorded after 7 days of exposure for the C2 treatment, which corresponded to the sampling time and condition with maximum cadmium bioaccumulation. Abnormal raphe formations (deviation from its lateral position) were significantly more abundant in the C2 treatment compared to the control. Molecular responses were related to cadmium level based on the number of genes impacted, intensity of the response and the frequency of observations. The expression of genes involved in the regulation of mitochondrial metabolism, photosynthesis, oxidative stress and silica metabolism was affected by cadmium exposure.