ABSTRACT
In response to changes in light quantity and quality the green algae Dunaliella salina Teod and Dunaliella tertiolecta Butcher can dramatically remodel their photosynthetic processes. Under low light conditions alterations occur that maximize light capture and utilization, while upon exposure to excess light, mechanisms are put in place that attempt to protect the photosynthetic apparatus from damage. Research with both D. salina and D. tertiolecta has revealed that these alterations can be detected within minutes of a change in irradiance and include adjustments in pigment and protein composition and abundance that are most often the result of changes in nuclear and chloroplastic gene expression. All photosynthetic organisms attempt to maintain a balance between the light energy absorbed by the photosystems with the capacity to use that light energy in metabolism. Evidence from work on Dunaliella indicates that this balance, or photostasis, is sensed by the photosynthetic electron transport chain, specifically the redox state of the plastoquinone pool. Acting as a sensor, the redox state of plastoquinone can modulate a wide range of activities including gene expression in the nucleus. Changes to the structure and function of the photosynthetic apparatus occur whenever this redox balance is upset which not only occurs in response to changes in irradiance, but also in response to environmental factors such as a change in temperature or nutrient availability that would alter the cell’s capacity to utilize the light energy absorbed.
