Mechanisms underlying silicon-dependent metal tolerance in the marine diatom Phaeodactylum tricornutum

Anthropogenic activities have significantly changed the stoichiometry and concentrations of nutrients in coastal waters. Silicon (Si) has become a potential limiting nutrient due to disproportionate nitrogen, phosphorus, and silicate inputs into these areas. The disrupted nutrient ratios can cause changes to metal sensitivity and accumulation in marine diatoms, an important group of eukaryotic phytoplankton that requires silicon for growth. In this study, we examined the effects of Si availability on the metal sensitivity in the diatom P. tricornutum. We found that Si starvation dramatically compromised its cadmium, copper, and lead tolerances. Interestingly, multiple lines of evidence indicated that Si-enriched cells had higher metal adsorption and influx rates than Si-starved cells. Yet Si-enriched cells also had a greater ability to respond to and counteract metal toxicity via elevated expression of membrane and vacuolar metal transporters and greater antioxidant activities which scavenge reactive oxygen species created by metal stress.