The state transition mechanism—simply depending on light-on and -off in Spirulina platensis

Abstract

The state transition in cyanobacteria is a long-discussed topic of how the photosynthetic machine regulates the excitation energy distribution in balance between the two photosystems. In the current work, whether the state transition is realized by "mobile phycobilisome (PBS)" or "energy spillover" has been clearly answered by monitoring the spectral responses of the intact cells of the cyanobacterium Spirulina platensis. Firstly, light-induced state transition depends completely on a movement of PBSs toward PSI or PSII while the redox-induced one on not only the "mobile PBS" but also an "energy spillover". Secondly, the "energy spillover" is triggered by dissociation of PSI trimers into the monomers which specially occurs under a case from light to dark, while the PSI monomers will re-aggregate into the trimers under a case from dark to light, i.e., the PSI oligomerization is reversibly regulated by light switch on and off. Thirdly, PSI oligomerization is regulated by the local H(+) concentration on the cytosol side of the thylakoid membranes, which in turn is regulated by light switch on and off. Fourthly, PSI oligomerization change is the only mechanism for the "energy spillover". Thus, it can be concluded that the "mobile PBS" is a common rule for light-induced state transition while the "energy spillover" is only a special case when dark condition is involved.

The dynamic behavior of phycobilisome movement during light state transitions in cyanobacterium Synechocystis PCC6803

“…Light-to-dark transition could result in a rise in H ? concentration on the stromal side and in turn a PSI monomerization, which would enhance probability for the two photosystems to meet each other, so lead to energy spillover from PSII to PSI for PSI, is a deeper energy trap (Li et al 2006). Up to now, PBS mobility is well believed to be mainly responsible for light state transitions but has never been experimentally observed.…”

New mechanism revealed for light-state transition in cyanobacterium Arthrospira platensis according to 77-K fluorescence kinetics

“…It has been proposed that light-state transition in cyanobacteria might involve the movement of membrane complexes and/or changes in the oligomerization states of the complexes (including PS II and PS I) [17,18]. It was found previously that PS I oligomerization states are reversibly variable under light-to-dark and dark-to-light transitions [12,19]. Apparently, either the movement of PS I or PS II or dissociation of PS I trimer into monomers may shorten the distance between PS I and PS II, amplify the effective concentration of PS I and enhance the spectral overlap of the PS I emission with PS II absorption, which certainly enhances the probability of uphill energy transfer.…”

“…Apparently, the state transition undergoes two successive sub-processes. In the first 4 min, the increase in C-PC and PS II fluorescence and the decrease in APC and PS I fluorescence suggests that PBSs move to PS II, which is a typical feature of transition from state 2 to state 1 [11,12], and the homogeneous kinetics of the PBS and photosystem fluorescence indicate that the state transition was regulated by mobile PBS. After 4 min, PS II and PS I components increased and decreased respectively, independent of the PBS components, suggesting energy spillover from PS I to PS II, which is referred to as inverse spillover in this work.…”

“…In cyanobacteria, "mobile phycobilisome (PBS)" [1,5] or "energy spillover" from PS II to PS I [6][7][8] has been proposed to explain the state transition. Previously, using glycine betaine to immobilize PBSs on thylakoid membranes [9,10], it was clarified that "mobile PBS" worked independently in light-induced state transitions while mobile PBS and energy spillover worked cooperatively in light-to-dark transition [11,12]. Light-state transitions in cyanobacteria were commonly studied in two discrete states, state 1 or state 2, while the intermediate processes were of less concern.…”

Identification of biochemical association of phycobilisome with photosystems in cyanobacterial state transition

“…The other forms of PSII and PSI are non-functional or unstable [7,26]. In addition, the PSI monomer functions in redoxinduced but not in light-induced State 1-State 2 transition [27]. In this study, therefore, we investigated the changes of association of PBS rod and core with the PSII dimer and PSI trimer caused by light-induced State 1-State 2 transition using a biochemical strategy in a unicellular cyanobacterium Synechocystis 6803.…”