Interactive effects of nitrogen and light on growth rates and RUBISCO content of small and large centric diatoms

Gang Li,Douglas A Campbell

doi:10.1007/s11120-016-0301-7

Abstract

Among marine phytoplankton groups, diatoms span the widest range of cell size, with resulting effects upon their nitrogen uptake, photosynthesis and growth responses to light. We grew two strains of marine centric diatoms differing by ~4 orders of magnitude in cell biovolume in high (enriched artificial seawater with ~500 µmol L−1 µmol L−1 NO3−) and lower-nitrogen (enriched artificial seawater with <10 µmol L−1 NO3−) media, across a range of growth light levels. Nitrogen and total protein per cell decreased with increasing growth light in both species when grown under the lower-nitrogen media. Cells growing under lower-nitrogen media increased their cellular allocation to RUBISCO and their rate of electron transport away from PSII, for the smaller diatom under low growth light and for the larger diatom across the range of growth lights. The smaller coastal diatom Thalassiosira pseudonana is able to exploit high nitrogen in growth media by up-regulating growth rate, but the same high-nitrogen growth media inhibits growth of the larger diatom species.

Highlights

Nitrogen is critical for marine phytoplankton to build abundant cellular materials including proteins and nucleic acids to support their growth and cell division (Finkel et al 2010; Wu et al 2014b; Li et al 2015)
Nitrogen availability can affect the cellular content of RUBISCO with consequent effects upon phytoplankton carbon assimilation (Wilhelm et al 2006), under N-limited conditions where RUBISCO has been suggested to act as an N reservoir in some species (Falkowski et al 1989)
The cell growth rate of T. pseudonana growing in HN media increased with growth light from low (*30 lmol photons m-2 s-1) to moderate levels (*180 lmol photons m-2 s-1) reaching a fitted lmax of 1.5 day-1 but decreased under higher light (Fig. 1a)

Summary

Introduction

Nitrogen is critical for marine phytoplankton to build abundant cellular materials including proteins and nucleic acids to support their growth and cell division (Finkel et al 2010; Wu et al 2014b; Li et al 2015). One of these nitrogen-rich materials the ribulose-1,5-bisphosphate carboxylase oxygenase (RUBISCO) protein is important, because this bifunctional enzyme catalyzes the initial step of photosynthetic carbon reduction by combining CO2 with ribulose-1,5-bisphosphate (RuBP) (Mizohata et al 2002), fixing inorganic carbon to organic matter (Kroth 2015). Diatoms span a wide size range across species from \2 lm to over 200 lm in equivalent spherical diameter, giving over eight orders of magnitude in cell volume (Beardall et al 2009)

Methods

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Discussion

Conclusion