Photoinhibition of photosystem II in Phytoplankton: Processes and patterns

All the diverse lineages of phytoplankters use conserved Photosystem II
complexes to mediate photochemical extraction of electrons from water,
with concomitant release of oxygen. Photosystem II suffers light-dependent
photoinactivation through multiple mechanisms, which is in turn countered
by protein subunit removal and replacement. This cycle imposes both direct
costs and also delayed opportunity costs. The effective quantum yield for
photoinactivation of Photosystem II depends upon taxa, cell size, prior
acclimation state, the instantaneous spectral regime and light level. Low
temperature or constraints upon metabolism can drive up excitation
pressure and photoinactivation, while slowing counteracting repair.
Environmental shifts in nutrients or CO2 alter resource allocations and
electron flows, with sometimes counter-intuitive effects upon
susceptibility to photoinactivation across taxa. These interacting factors
generate a wide range of susceptibilities to photoinactivation across
phytoplankton cells. Some phytoplankters engage in luxury or pre-emptive
recycling of Photosystem II proteins before photoinactivation occurs, and
some accumulate large pools of Photosystem II proteins outside active
complexes, which may relate to the diverse thylakoid architectures across
taxa. These interacting factors generate complex cost-benefit tradeoffs to
maintain Photosystem II, and thus the range of conditions where oxygenic
photosynthesis is feasible for a given taxa.