THE CHEMICAL FORM OF DISSOLVED SI TAKEN UP BY MARINE DIATOMS

摘要: Results of past studies the pH-dependent Si uptake kinetics Phaeodactylum tricornutum Bohlin suggested that anion SiO(OH) is chemical form dissolved taken up by marine diatoms. We determined three other diatom species and P. examining use under two dramatically different SiO(OH):Si(OH)4 ratios in seawater varying pH from ≈8 to ≈9.6. Uptake rates were using a precise sensitive 32Si tracer methodology. The obtained for all except suggest diatoms transport Si(OH)4. half-saturation constant (Km) varies strongly as function when substrate assumed be SiO(OH). Kinetic curves Thalassiosira pseudonana (Hustedt) Hasle et Heimdal, weissflogii (Grunow) G. Fryxell Hasle, Cylindrotheca fusiformis Reimann Lewin have statistically identical values Km at each Si(OH)4 (T. T. weissflogii) or total silicon (C. fusiformis). In contrast, exhibits unusual biphasic kinetics: conforms Michaelis–Menten 15 25 μM, above which increases linearly. This enigmatic response may biased conclusions drawn experiments this species. However, based on consistency results species, new model proposed basis direct formation complex between Si-transport protein