Limits...
The dinoflagellate Lingulodinium polyedrum responds to N depletion by a polarized deposition of starch and lipid bodies.

Dagenais Bellefeuille S, Dorion S, Rivoal J, Morse D - PLoS ONE (2014)

Bottom Line: While blooms are often associated with high available nitrogen, there are instances where they are observed in oligotrophic environments.Photosynthesis is maintained at high levels for roughly a week following nitrate depletion, resulting in accumulated photosynthetic products in the form of starch.During the second week, photosynthesis rates decrease due to a reduction in the number of chloroplasts and the accumulation of neutral lipid droplets.

View Article: PubMed Central - PubMed

Affiliation: Institut de Recherche en Biologie Végétale, Département de Sciences Biologiques, Université de Montréal, Montréal, Québec, Canada.

ABSTRACT
Dinoflagellates are important contributors to the marine phytoplankton and global carbon fixation, but are also infamous for their ability to form the spectacular harmful algal blooms called red tides. While blooms are often associated with high available nitrogen, there are instances where they are observed in oligotrophic environments. In order to maintain their massive population in conditions of nitrogen limitation, dinoflagellates must have evolved efficient adaptive mechanisms. Here we report the physiological responses to nitrogen deprivation in Lingulodinium polyedrum. We find that this species reacts to nitrogen stress, as do most plants and microalgae, by stopping cell growth and diminishing levels of internal nitrogen, in particular in the form of protein and chlorophyll. Photosynthesis is maintained at high levels for roughly a week following nitrate depletion, resulting in accumulated photosynthetic products in the form of starch. During the second week, photosynthesis rates decrease due to a reduction in the number of chloroplasts and the accumulation of neutral lipid droplets. Surprisingly, the starch granules and lipid droplets are seen to accumulate at opposite poles of the cell. Lastly, we observe that cells acclimated to nitrogen-depleted conditions resume normal growth after addition of inorganic nitrogen, but are able to maintain high cell densities far longer than cells grown continuously in nitrogen-replete conditions.

Show MeSH

Related in: MedlinePlus

Polarized localization of lipid bodies and starch granules visualized by transmission electron microscopy.Cross-sections of a cell at day 0 (A) and at day 14 in f/2-N medium (B). Both are in a ventral orientation and scale bars are 10 µm. Lipid bodies (l) are located predominantly at the anterior (a) end of the cell, while starch granules (s) are localized at the posterior (p) end. The ends of the C-shaped nucleus (n) surround a central Golgi/ER membrane region (m). Chloroplasts (c) are less abundant in day 14 cells. Higher magnification images of lipid bodies (C) and starch granules (D) in a cell at day 14. Scale bars are 1 µm.
© Copyright Policy
Related In: Results  -  Collection

License
getmorefigures.php?uid=PMC4219697&req=5

pone-0111067-g007: Polarized localization of lipid bodies and starch granules visualized by transmission electron microscopy.Cross-sections of a cell at day 0 (A) and at day 14 in f/2-N medium (B). Both are in a ventral orientation and scale bars are 10 µm. Lipid bodies (l) are located predominantly at the anterior (a) end of the cell, while starch granules (s) are localized at the posterior (p) end. The ends of the C-shaped nucleus (n) surround a central Golgi/ER membrane region (m). Chloroplasts (c) are less abundant in day 14 cells. Higher magnification images of lipid bodies (C) and starch granules (D) in a cell at day 14. Scale bars are 1 µm.

Mentions: To confirm the asymmetrical distribution of TAGs and starch granules, cells were examined using transmission electron microscopy to visualize both types of C stores in the same cell (Fig 7). Cells at day 0 and day 14 cells were fixed at LD 0, a time at which neither lipid bodies nor starch were observed in the day 0 cell (Fig. 7A). However, the two types of C stores have clearly accumulated at opposite ends of the cell by 14 days in f/2-N medium (Fig. 7B). Lipid bodies are located at the anterior end and appear dark due to the lipophilic nature of the osmium tetroxide stain used to contrast the sections (Fig. 7C) while starch granules appear white and are located at the posterior end of the cell (Fig. 7D). The white striations observed in the lipid droplets are likely due to a sectioning artifact, as their orientation is the same for all cells in a section independent of how the individual cells are orientated in the section. Lastly, we also note that chloroplasts appear smaller and are less abundant in the day 14 cell when compared to the day 0 cell, in agreement with the confocal images (Fig. 4D, G, J).


The dinoflagellate Lingulodinium polyedrum responds to N depletion by a polarized deposition of starch and lipid bodies.

Dagenais Bellefeuille S, Dorion S, Rivoal J, Morse D - PLoS ONE (2014)

Polarized localization of lipid bodies and starch granules visualized by transmission electron microscopy.Cross-sections of a cell at day 0 (A) and at day 14 in f/2-N medium (B). Both are in a ventral orientation and scale bars are 10 µm. Lipid bodies (l) are located predominantly at the anterior (a) end of the cell, while starch granules (s) are localized at the posterior (p) end. The ends of the C-shaped nucleus (n) surround a central Golgi/ER membrane region (m). Chloroplasts (c) are less abundant in day 14 cells. Higher magnification images of lipid bodies (C) and starch granules (D) in a cell at day 14. Scale bars are 1 µm.
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4219697&req=5

pone-0111067-g007: Polarized localization of lipid bodies and starch granules visualized by transmission electron microscopy.Cross-sections of a cell at day 0 (A) and at day 14 in f/2-N medium (B). Both are in a ventral orientation and scale bars are 10 µm. Lipid bodies (l) are located predominantly at the anterior (a) end of the cell, while starch granules (s) are localized at the posterior (p) end. The ends of the C-shaped nucleus (n) surround a central Golgi/ER membrane region (m). Chloroplasts (c) are less abundant in day 14 cells. Higher magnification images of lipid bodies (C) and starch granules (D) in a cell at day 14. Scale bars are 1 µm.
Mentions: To confirm the asymmetrical distribution of TAGs and starch granules, cells were examined using transmission electron microscopy to visualize both types of C stores in the same cell (Fig 7). Cells at day 0 and day 14 cells were fixed at LD 0, a time at which neither lipid bodies nor starch were observed in the day 0 cell (Fig. 7A). However, the two types of C stores have clearly accumulated at opposite ends of the cell by 14 days in f/2-N medium (Fig. 7B). Lipid bodies are located at the anterior end and appear dark due to the lipophilic nature of the osmium tetroxide stain used to contrast the sections (Fig. 7C) while starch granules appear white and are located at the posterior end of the cell (Fig. 7D). The white striations observed in the lipid droplets are likely due to a sectioning artifact, as their orientation is the same for all cells in a section independent of how the individual cells are orientated in the section. Lastly, we also note that chloroplasts appear smaller and are less abundant in the day 14 cell when compared to the day 0 cell, in agreement with the confocal images (Fig. 4D, G, J).

Bottom Line: While blooms are often associated with high available nitrogen, there are instances where they are observed in oligotrophic environments.Photosynthesis is maintained at high levels for roughly a week following nitrate depletion, resulting in accumulated photosynthetic products in the form of starch.During the second week, photosynthesis rates decrease due to a reduction in the number of chloroplasts and the accumulation of neutral lipid droplets.

View Article: PubMed Central - PubMed

Affiliation: Institut de Recherche en Biologie Végétale, Département de Sciences Biologiques, Université de Montréal, Montréal, Québec, Canada.

ABSTRACT
Dinoflagellates are important contributors to the marine phytoplankton and global carbon fixation, but are also infamous for their ability to form the spectacular harmful algal blooms called red tides. While blooms are often associated with high available nitrogen, there are instances where they are observed in oligotrophic environments. In order to maintain their massive population in conditions of nitrogen limitation, dinoflagellates must have evolved efficient adaptive mechanisms. Here we report the physiological responses to nitrogen deprivation in Lingulodinium polyedrum. We find that this species reacts to nitrogen stress, as do most plants and microalgae, by stopping cell growth and diminishing levels of internal nitrogen, in particular in the form of protein and chlorophyll. Photosynthesis is maintained at high levels for roughly a week following nitrate depletion, resulting in accumulated photosynthetic products in the form of starch. During the second week, photosynthesis rates decrease due to a reduction in the number of chloroplasts and the accumulation of neutral lipid droplets. Surprisingly, the starch granules and lipid droplets are seen to accumulate at opposite poles of the cell. Lastly, we observe that cells acclimated to nitrogen-depleted conditions resume normal growth after addition of inorganic nitrogen, but are able to maintain high cell densities far longer than cells grown continuously in nitrogen-replete conditions.

Show MeSH
Related in: MedlinePlus