Pathways of photosynthetic electron flow under environmental stress

We track the light-induced electron transfers in situ in leaves working under defined environmental conditions.

The two photosystems in the chloroplast work in series to deliver electrons from the substrate water to NADP+ in two light-driven uphill steps, conserving the light energy as chemical energy in NADPH and ATP. In addition to this linear electron flow, there is a cyclic electron pathway mediated by ferredoxin around Photosystem I, another Photosystem I cyclic pathway involving NADPH, a Q cycle around the cytochrome bf complex, as well as electron donation from stromal reductants (see an larger version of the diagram here).

A challenge is to quantify these separate electron fluxes, all except one of which pass through P700, the primary electron donor in Photosystem I, and to do so in leaves without having to isolate the chloroplasts. How do these fluxes vary under different environmental conditions? What roles do the electron fluxes play in the protection of the photosynthetic apparatus under environmental stress, such as high light and/or drought? The overall goal is to decipher the various electron fluxes in situ, within leaves that are functioning in defined environmental conditions.