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.

Methods
File: PhytoplanktonPhotoinactivationData
Types of data: Categorical and numeric data on environmental and growth conditions for the analyzed phytoplankton, and numeric data on parameters quantifying the photoinactivation and repair of Photosystem II across the analyzed phytoplankton.

Data processing: Phytoplankton Photosystem II functional data was collated from the laboratory archives of D.A. Campbell and  J. Serôdio, and from published sources.

Plots of Photosystem II function vs. time or vs. cumulative incident photons were used to extract parameters for Photosystem II photoinactivation, and for counteracting repair of Photosystem II. Fitting equations are described in the accompanying book chapter, and in
Campbell DA, Tyystjärvi E (2012) Parameterization of photosystem II photoinactivation and repair. Biochimica et Biophysica Acta (BBA) - Bioenergetics 1817:258–265. doi: 10.1016/j.bbabio.2011.04.010

Data collation was performed under macOS 10.13.2 using Microsoft Excel for Mac 16.16.1.  Curve fitting was performed using R 3.5.0 running under RStudio 1.1.453, with non-linear least squares analyses through minpack.lm: R Interface to the Levenberg-Marquardt Nonlinear Least-Squares
Algorithm Found in MINPACK, Plus Support for Bounds, Timur V. Elzhov, Katharine M. Mullen, Andrej-Nikolai Spiess and Ben Bolker 2016, R package version 1.2-1, https://CRAN.R-project.org/package=minpack.lm.