Figure 2.

A model for the co-option of acclimation responses into somatic cell differentiation in V. carteri (R and S denote reproductive and somatic cells); see text for discussion. Although many components are involved, for simplicity, changes in the redox status are symbolized by the over-reduction of the NADP pool (vertical red arrows) owing to either decreased NADPH consumption in nutrient-deprived Chlamydomonas or excess of excitation energy (owing to a higher surface/volume ratio) in Volvox somatic cells. The switch to cyclic electron transport (CET), which can maintain ATP synthesis (and thus vital processes) in acclimated Chlamydomonas cells (Eberhard et al. 2008) and possibly in Volvox somatic cells, is also indicated.