Photosynthetic Acclimation and Adaptation to Cold Ecosystems

Abstract

Cold-tolerant, photosynthetic organisms are able to either acclimate or, alternatively, adapt to low temperatures. The former are designated as psychrotolerant phototrophs, whereas the latter are defined as psychrophilic phototrophs. Central to cold acclimation and cold adaptation in phototrophs is the capacity to respond to excess excitation energy. This requires the integration of both low temperature sensing/signal transduction pathways and light sensing/signal transduction mechanisms to maintain photostasis, that is, cellular energy balance. The generation of excess excitation energy by high light is mimicked by exposure to low temperatures. Although modulation of the redox state of the photosynthetic apparatus is a common feature in sensing excess excitation energy, the response to this redox sensing/signalling mechanism is species dependent. These concepts are discussed with respect to acclimation and adaptation of green algae, cyanobacteria, and terrestrial plants to the extreme environments represented by the Antarctic and Arctic ecosystems. Our comparative discussions illustrate that phototrophs have evolved different strategies to deal with excess excitation energy which results in an impressive array of phenotypes in response to acclimation and adaptation to cold environments. Consequently, we conclude that the photosynthetic apparatus is not only a critical energy transformer for all phototrophs, but it is also a crucial sensor of the abiotic environment. Furthermore, our comparative analyses of green algae, cyanobacteria, and terrestrial plants native to Antarctic and Arctic ecosystems clearly indicate that psychrophily is not essential for survival in these extreme cold environments. We suggest that there is an urgent need for more comprehensive research focussed on the physiology, biochemistry, genomics, and metabolomics of the myriad, yet undiscovered, organisms that inhabit these extreme environments, which may provide novel biotechnological applications to industry, agriculture, and medicine.