title: Effects of silicate resupply to silicate-deprived Thalassiosira weissflogii (Bacillariophyceae) in stationary or senescent phase: short-term patterns of growth and cell death.
abstract: The ability of nutrient-deprived phytoplankton to recover in the short term when nutrients are resupplied has been studied for nitrogen and phosphorus, but the case for silicate (Si) is poorly understood. Si-limited Thalassiosira weissflogii (Grunow) Fryxell et Hasle (grown in batch culture) was harvested in stationary phase (when cell numbers stopped increasing ~2 d after Si depletion) and senescence (when cell numbers declined ~4 d after Si depletion) and Si was resupplied at different concentrations (from 0 to 100 μM). Cell numbers, proportion of dead cells, variable fluorescence emissions (Fv /Fm ), and activities of proteases were measured during Si depletion and for 24 h after Si resupply. As Si was depleted, the specific growth rate declined, dead cells increased from ~2% in log phase, to ~25% in stationary phase to over 35% in senescence, and activities of proteases associated with cell death increased several-fold. Concentration-dependent recovery of growth rate was seen after 24 h for cultures resupplied with Si in stationary phase but not in senescence. However, resupply of Si at 100 μM to stationary phase cultures alone increased protease activity to nearly the levels seen in senescence. Differences in the responses to Si resupply suggest that the ability and time to recover from Si depletion depend not only on the growth phase but also on the concentration resupplied.
authors.affiliation: Institute of Ocean Science and Technology, Graduate School at Shenzhen, Tsinghua University, Shenzhen, 518055, China.|Division of Environment, The Hong Kong University of Science and Technology, Clear Water Bay, Kowloon, Hong Kong.
authors.forename: Yuelu
authors.initials: Y
authors.lastname: Jiang
authors.affiliation: School of Marine Sciences, Sun Yat-Sen University, Guangzhou, 510275, China.|Environmental Futures Centre, Griffith University, Brisbane, Queensland, 4111, Australia.
authors.forename: Kedong
authors.initials: K
authors.lastname: Yin
authors.affiliation: Department of Biological Sciences and School of Freshwater Sciences, University of Wisconsin-Milwaukee, Milwaukee, Wisconsin, 53201, USA.
authors.forename: John A
authors.initials: JA
authors.lastname: Berges
authors.affiliation: Division of Environment, The Hong Kong University of Science and Technology, Clear Water Bay, Kowloon, Hong Kong.|Department Earth & Ocean Sciences, University of British Columbia, Vancouver, British Colombia, Canada, V6T 1Z4.
authors.forename: Paul J
authors.initials: PJ
authors.lastname: Harrison
keywords: Fv/Fm; Si limitation; caspase-like proteases; cell death