Chloroplasts, the tiny photosynthetic energy factories of plant cells, were observed to move in response to light and temperature as long as a century ago. Within a cell, these organelles can migrate towards the cell wall closest to a light source, thereby optimising photosynthesis. They do, however, move away from very strong light, presumably to escape photodamage. In low temperature conditions, chloroplasts move away from the cell wall closest to the outside world. This temperature response is less well understood than the response to light, and a recent Plant, Cell and Environment study revisited these experiments on the liverwort, Marchantia polymorpha (pictured), and also looked at the mobility of other organelles induced by low temperatures.
In cold conditions, chloroplasts move, within the cell where they find themselves, towards the centre of the plant. This movement appears to be mediated by actin filaments, which are positioned at the “front” of the chloroplast (in terms of its direction of movement). Although not completely understood, the movement of chloroplasts in response to cold has been seen in evergreen but not in deciduous ferns. This suggests that it may play a role in the cold resistance mechanisms of plants. Intriguingly, plant cell nuclei have also been observed to migrate away from bright light. This could be explained as an avoidance mechanism against ultraviolet DNA damage. M. polymorpha nuclei also move towards the centre of the plant in cold temperatures. The authors speculate that this could represent a migration to a slightly warmer intracellular environment, where the activity of DNA-repairing enzymes would be less impaired.
New techniques provide us with opportunities to better understand both the mechanisms and reasons underlying organelle migration in response to environmental conditions, and the authors suggest several potential lines of further research.
Ogasawara Y., Ishizaki K., Kohchi T. & Kodama Y. (2013). Cold-induced organelle relocation in the liverwort Marchantia polymorpha L., Plant, cell & environment, DOI: 10.1111/pce.12085
The liverwort Marchantia polymorph. Photograph by Cathy Shields.