Dynamics of formation and secretion of heterococcoliths byCoccolithus pelagicusssp.braarudii

Abstract

The formation and secretion of heterococcoliths by the non-motile life phase of the coccolithophore Coccolithus pelagicus was investigated using electron microscopy and time-lapse bright field imaging. Coccolithogenesis in C. pelagicus exhibited sequential mineralization of single coccoliths in Golgi-derived and nuclear-associated vesicles, a pattern similar to the formation of heterococcoliths in Emiliania huxleyi. Our TEM data show that only on maturation does the single coccolith vesicle migrate away from the nucleus before secretion. A reticular body, distinct from the Golgi body, was also clearly visible at the distal surface of the developing coccolith vesicle, suggesting this is a common structural feature in placolith cells that mineralize and secrete coccoliths one at a time. Time-lapse imaging revealed that the coccolith secretion process is rapid, taking 60-190 seconds, and involves considerable contractile activity to eject and position the coccolith on the surface of the cell. An intact flagellar root apparatus was discovered at the anterior pole of this non-motile cell from which polarized secretion of coccoliths occurs, which may indicate a novel role for such cytoskeletal structures. Freeze-fracture preparations revealed columnar deposits and adhesions linking the scales and coccolith baseplates to the cell, across the periplasmic space providing points of attachment for cellular movement. Rotatory movements of the cell relative to external coccoliths were exhibited by all actively calcifying cells. These movements enable the cell, while exhibiting morphologically polarized secretion, to locate and secrete a mature coccolith in a spatially well-defined manner. Finally, the time-lapse imaging approach described here provides an opportunity to quantify the regulation of coccolith production in single cells with high temporal resolution allowing responses of calcification to rapidly fluctuating environmental conditions such as light-dark transitions to be examined in detail, which has not been possible with bulk calcification studies.

High temperature decreases the PIC / POC ratio and increases phosphorus requirements in <i>Coccolithus pelagicus</i> (Haptophyta)

“…The exponential growth rate of subsp. braarudii was similar to those determined previously under similar experimental conditions (Taylor et al, 2007;Buitenhuis et al, 2008). Although other studies have observed higher exponential growth rates (up to 0.9 d −1 ) for the same strain (Langer et al, 2006;Krug et al, 2011), these authors used a higher irradiance and a longer light phase which probably increased cell division rates.…”

Photoacclimation to abrupt changes in light intensity by Phaeodactylum tricornutum and Emiliania huxleyi: the role of calcification

“…In Emiliania huxleyi, Ca 2+ is thought to cross the plasma membrane through channels following its electrochemical gradient, then being transported into the endoplasmic reticulum and calcification vesicle potentially by ATP-dependent pumps or ion exchangers (possibly with H + ) and Ca 2+ -ATPase, respectively (Mackinder et al 2011). The rapid increase in inorganic carbon fixation already after 10 min could be linked to an increased calcification rate together with faster exudation of coccoliths (E. huxleyi produces about 1 coccolith h −1 , Paasche 2001) similarly to Coccolithus pelagicus (Taylor et al 2007). …”

Physiology regulates the relationship between coccosphere geometry and growth phase in coccolithophores

“…Thus far, relatively common fossil coccospheres have been documented from at least 24 localities (Burns, 1975;Covington, 1985;Lambert, 1987;Young and Bown, 1991;Mai, 1997;Mai et al, 1998;Henderiks, 2008;Ciurej, 2010;Bown et al, 2014) representing low to high latitudes, the North and South Atlantic oceans, the North Pacific Ocean, the Indian Ocean and Southern Ocean, and ranging from Kimmeridgian (Late Jurassic) to Pleistocene. Coccosphere geometry analysis is therefore likely to prove applicable at a range of localities and time intervals, but reasoned selection of sampling sections is likely to be important for retrieving sufficient coccospheres for robust data analysis.…”

“…The relationship between growth phase, ∅ and C N can be understood by considering the process of cell division and how it is affected by the nutrient depletion that instigates non-exponential-phase growth. Both ∅ and C N vary as each cell progresses through the cell division cycle (unpublished observations; Taylor et al, 2007;Müller et al, 2008). Recently divided cells are small, with approximately the minimum number of coccoliths required to form a complete cell covering (unpublished observations; Fig.…”