Dynamics of photosystem II heterogeneity in Dunaliella salina (green algae)

Abstract

Based on the electron-transport properties on the reducing side of the reaction center, photosystem II (PS II) in green plants and algae occurs in two distinct forms. Centers with efficient electron-transport from QA to plastoquinone (QB-reducing) account for 75% of the total PS II in the thylakoid membrane. Centers that are photochemically competent but unable to transfer electrons from QA to QB (QB-nonreducing) account for the remaining 25% of total PS II and do not participate in plastoquinone reduction. In Dunaliella salina, the pool size of QB-nonreducing centers changes transiently when the light regime is perturbed during cell growth. In cells grown under moderate illumination intensity (500 μE m(-2)s(-1)), dark incubation induces an increase (half-time 45 min) in the QB-nonreducing pool size from 25% to 35% of the total PS II. Subsequent illumination of these cells restores the steady-state concentration of QB-nonreducing centers to 25%. In cells grown under low illumination intensity (30 µE m(-2)s(-1)), dark incubation elicits no change in the relative concentration of QB-nonreducing centers. However, a transfer of low-light grown cells to moderate light induces a rapid (half-time 10 min) decrease in the QB-nonreducing pool size and a concomitant increase in the QB-reducing pool size. These and other results are explained in terms of a pool of QB-nonreducing centers existing in a steady-state relationship with QB-reducing centers and with a photochemically silent form of PS II in the thylakoid membrane of D. salina. It is proposed that QB-nonreducing centers are an intermediate stage in the process of damage and repair of PS II. It is further proposed that cells regulate the inflow and outflow of centers from the QB-nonreducing pool to maintain a constant pool size of QB-nonreducing centers in the thylakoid membrane.

Two components of onset and recovery during photoinhibition of Ulva rotundata

“…This process is accelerated, and recovery is completely prevented, by CAP, an inhibitor of chloroplast protein synthesis. We suspect that this process may reflect photoinhibitory damage to PSII involving loss of PSII functions, perhaps based on the dynamics of the D1 polypeptide of the reaction center, as has been explored in other studies (Chow et al 1989;Aro et al 1990;Guenther and Melis 1990;Richter et al 1990;Ohad et al 1990).…”

Tansley Review No. 117

“…However, a remarkable feature of plant and algal chloroplasts, as well as cyanobacteria, is their ability to adjust their photosynthetic apparatus in relation to available irradiance. Short-term acclimation is achieved through so-called transitions from State I to State II whereby electron transport through the two photosystems can be adjusted in relation to light quality and\or the relative demands for ATP and NADPH (Manodori & Melis, 1984 ;Allen et al, 1989 ;Guenther & Melis, 1990). Longer-term acclimation involves regulation of the relative abundances of the various proteins of the photosynthetic apparatus in relation to irradiance during growth.…”

Development of Photosystem II in dark grown Chlamydomonas reinhardtii. A light-dependent conversion of PS II?, QB-nonreducing centers to the PS II?, QB-reducing form

“…In recent work it was shown that light plays a role in modulating the pool size of the QBnonreducing centers (Guenther and Melis 1989b).…”

“…In recent work the question of the pool size and pool dynamics of PS II QB-nonreducing centers in D. salina was addressed (Guenther and Melis 1989b). It was found that the pool size of QBnonreducing centers was maintained at a steadystate level under continuous illumination.…”