# Photosynthesis and light absorption in the large marine dinoflagellate, {\it Pyrocystis noctiluca\/} Murray {\it ex\/} Haeckel (1890) grown in laboratory culture

#### Abstract

Pyrocystis noctiluca is a large photosynthetic dinoflagellate. The hypotheses addressed here concern the ecological significance of: (1) the physiological limitations on light absorption experienced by P. noctiluca in a low-light environment dominated by smaller phytoplankton species, and (2) the physiological changes through its cell cycle.^ Pyrocystis noctiluca achieved maximum division rates near 0.2 day$\sp{-1}$. At low irradiances, division rates became light-limited and cells responded by decreasing cell biomass. Pigment ratios were invariant at all light intensities. The ratio of carbon:cell decreased more than that of chla:cell resulting in an increase in chla C$\sp{-1}$ and chla cell volume$\sp{-1}$ in cells acclimated to low irradiances. This increase in cellular pigment concentration resulted in an unusual increase (rather than the typical decrease) in the chlorophyll-specific absorption coefficient (k$\sb{\rm chl})$ in these cultures. Pyrocystis noctiluca appears to avoid self-shading between adjacent chloroplasts by redistributing its plastids through the cytoplasm.^ The movement of chloroplasts was determined to be a blue-light-mediated response (karyostrophy). Using an empirically-derived relationship between blue light intensity and degree of chloroplast movement, the photon absorption rate was modeled for a hypothetical P. noctiluca cell situated at any depth in an optically clear water column. Possible adaptive advantages for this light-mediated chloroplast movement response are protection from harmful UVB and high intensity blue light in surface waters, and the ability to increase photon absorption efficiency at low irradiances.^ Photosynthetic parameters were all found to vary through the cell development cycle of P. noctiluca. Chla cell$\rm\sp{-1},\ k\sb{cell}$, and P$\sb{\rm max}$ increased through the cell division cycle. Commensurate increases in $\rm k\sb{cell},\ \alpha$ and $\rm\phi\sb{max}$ suggested increased efficiencies in the utilization of absorbed photons for photosynthesis at irradiances below light saturation. In experiments where light intensity steadily increased or decreased it was found that all photosynthetic and bio-optical parameters except P$\sb{\rm max}$ were influenced more by the processes related to cell division than to the light regime. The observed increases in P$\sb{\rm max}$ suggested that this species has the ability to adapt quickly to transient increases in light intensity. ^

#### Subject Area

Biology, Oceanography|Biology, Plant Physiology

#### Recommended Citation

Robert David Vaillancourt, "Photosynthesis and light absorption in the large marine dinoflagellate, {\it Pyrocystis noctiluca\/} Murray {\it ex\/} Haeckel (1890) grown in laboratory culture" (1995). Dissertations and Master's Theses (Campus Access). Paper AAI9702115.
http://digitalcommons.uri.edu/dissertations/AAI9702115

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