Temperature-Dependent Sensitivity of a Marine Diatom to Cadmium Stress Explained by Subcelluar Distribution and Thiol Synthesis

This study examined the potential bioaccumulation and biochemical mechanisms (phytochelatin and other thiols induction) in the temperature-dependent sensitivity of a marine diatom Thalassiosira nordenskioeldii to cadmium (Cd) stress. A higher environmental temperature increased the sensitivity of diatoms to Cd toxicity. Either increased cellular Cd accumulation or a poorer detoxification ability was responsible for the higher concentration of metal-sensitive fraction (MSF)-Cd in the diatoms and subsequently the higher Cd sensitivity with increasing temperature. In addition, N-deficiency or glutathione depletion may partly explain the highest sensitivity at the highest tested temperature (30.5 degrees C). Although temperature affected the biochemical composition (e.g., the N/C ratio and phytochelatin induction), physiological processes (e.g., the growth rate, photosynthesis, Cd uptake, accumulation, and subcellular distribution) and the resulting differential tolerances, Cd concentration in MSF or organelles served as the best indicators of Cd toxicity in diatoms at different temperatures. Phytochelatins (PCs) were induced by increasing [Cd2+] and the significant relationship between the intracellular Cd and PC-SH concentration suggested that PC-SH is a biomarker for cellular metal stress. However, the intracellular Cd/ PC-SH ratio did not always explain the temperature-dependent metal tolerance. The functions of PCs other than metal chelation and detoxification need to be further examined.