GROWTH CHARACTERISTICS OF MARINE PHYTOPLANKTON DETERMINED BY CELL CYCLE PROTEINS: THE CELL CYCLE OF ETHMODISCUS REX (BACILLARIOPHYCEAE) IN THE SOUTHWESTERN NORTH ATLANTIC OCEAN AND CARIBBEAN SEA¹

Abstract

Ethmodiscus spp. is an important contributor to oceanic tropical‐ooze sediments and thus might be an important transport vehicle of carbon from the ocean surface to sediments. The knowledge of its cell cycle and growth rate, which is still lacking, is necessary to evaluate the importance of Ethmodiscus in nutrient cycling and to solve the discrepancy between its high sedimentary abundance and rarity in the plankton. We used immunofluorescence of a cell cycle protein, prolqerating cell nuclear antigen (PCNA), and DNA‐specific staining to study the progression of the cell cycle and roughly estimate the growth rate for E. rex (Rattray) Wiseman and Hendey in the southwestern North Atlantic Ocean and Caribbean Sea in June 1994 and January 1995. During the cell division cycle, the chloroplasts appeared to synthesize DNA before the nucleus (S phase). Following the S phase, the nucleus moved from one end of the cell toward the center underneath the midline of the girdle band (G2 phase) where it divided (M phase). During a very brief period, the parent cell split and moved apart from the girdle midline, and two new valves were produced (late M phase). The two daughter nuclei apparently remained attached at the joint of the two newly produced valves, where they appeared to be responsible for coordinating the symmetrical formation of the new valves. The morphologically complete daughter cells remained joined for a short period of time before separating into solitary cells whose nucleus was located at one end of the cell. Derived from the phase fraction curves, the duration of the cell cycle phases decreased in the order from G1, S, G2, to M. A conservative estimate of the growth rate in the study area obtained by using PCNA immunostaining was 0.39–0.46 d−1 in June and 0.15 d−1 in January. The validity and implication of the growth rate estimates are discussed.

Cooccurrence of ScDSP Gene Expression, Cell Death, and DNA Fragmentation in a Marine Diatom, Skeletonema costatum

“…Several molecular markers, such as rbcL (ribulose-1,5-bisphosphate carboxylase/oxygenase) and PCNA (proliferating cell nuclear antigen), have already been applied to evaluate the growth potential of eukaryotic phytoplankton in the field (27,44). A common feature of these genes is that they are all more actively expressed when phytoplankton cells are rapidly growing.…”

Modeling Size-dependent Photosynthesis: Light Absorption and the Allometric Rule

“…Phytoplankton make ideal experimental organisms for allometric studies, due to their extremely large size range. Phytoplankton include picoplankton which have diameters as small as 1 m to netplankton that can reach diameters of close to a millimeter (Raven, 1994;Lin & Carpenter, 1995). Phytoplankton size is a good predictor of a variety of ecologically relevant rates.…”

Algal growth rate fluctuations observed under uniform ambient test conditions using static and semicontinuous assay techniques

“…Growth rate fluctuations were consistent with a high degree of cell‐cycle synchronization. A morphological or biochemical cell‐cycle marker could accurately quantify synchronization [18,24,25] but, indirect evidence suggested it was high immediately following inoculation of the semicontinuous assay. Average population doubling times during this assay were computed to be approximately 10 h, but individual S. capricornutum are reported to divide normally into four autospores [10,26].…”