Over-production of the D1:2 protein makes Synechococcus cells more tolerant to photoinhibition of photosystem II

Abstract

Over-expression of the psbAIII gene encoding for the D1 protein (form II; D1:2) of the photosystem II reaction centre in the Synechococcus sp. PCC 7942 was studied using a tac promoter and the lacIQ system. Over-expression was induced with 40 microgram/ml IPTG in the growth medium for either 6 or 12 h at growth irradiance (50 mumol photons m-2 s-1). This treatment doubled the amount of psbAII/III mRNA and the D1:2 protein in membranes but decreased the amount of psbAI messages and the D1:1 protein. The total amount of both heterodimeric reaction centre proteins, D1 and D2, remained constant under growth light conditions, indicating that the number of PSII centres in the membranes was not affected, only the form of the D1 protein was changed from D1:1 to D1:2 in most centres. When the cells were photoinhibited either at 500 or 1000 mumol photons m-2 s-1, in the presence or absence of the protein synthesis inhibitor lincomycin, the D1:2 protein remained at a higher level in cells in which over-expression had been induced by IPTG. These cells were also less prone to photoinhibition of PSII. It is suggested that the tolerance of cells to photoinhibition increases when most PSII reaction centres contain the D1:2 protein at the beginning of high irradiance. This tolerance is further strengthened by maintaining psbAIII gene over-expression during the photoinhibitory treatment.

Resistance to photoinhibition of photosystem II and catalase and antioxidative protection in high mountain plants

“…The cyanobacterium Synechococcus (PCC 7942) contains two different forms of the D1 protein that give rise to PSII centres differing in quantum yield and in their capacity to quench excitation energy. Overproduetion of form II of the D1 protein makes Synechococcus cells more tolerant to photoinhibition of PSII (Soitamo et al 1996). This example demonstrates that proteins with different structural properties have evolved and may be utilized for different functional requirements.…”

UVB Effects on the Photosystem II‐D1 Protein of Phytoplankton and Natural Phytoplankton Communities

“…l), is also degraded in the light and although the pattern of D2 degradation mirrors that of D 1, the half-life durations of the D2 protein are about 3 times longer than those of D1 (124). In other studies the UV-driven degradation of the D1 protein was synergistically accelerated in the presence of (121,122). In the presence of a D1 protein destruction of the D1 protein and in variable fluorescence during the initial 12 h of UV exposure followed by a rapid D1 resynthesis beyond 24 h under the same exposure 1 in photosynthetic 0 2 evolution and in DI content followed by recovery under dim light for the cells that were previously exposed to the full solar spectrum but not for those cells previously exposed to UVB only evolution after 2 h under UVB (with a PAR background) with partial recovery of photosynthetic activity after 24 h under visible light only.…”

“…In another study performed on Synechococcus PCC 7942 deprived of PSII repair by blockage of D1 synthesis with chloramphenicol, results showed a good correlation between the rate of exchange of the low‐light D1 form (D1:1) for the high‐light D1 form (D1:2) and the rate of PSII photoinhibition, thereby confirming that photoinhibition triggers the exchange of D1 proteins (119) (Table 1). Interestingly, cyanobacteria, in which most PSII RCs contain the D1:2 protein at the beginning of high irradiance, are less prone to photoinhibition (121,122).…”

Expression of a Ketolase Gene Mediates the Synthesis of Canthaxanthin in Synechococcus Leading to Tolerance Against Photoinhibition, Pigment Degradation and UV-B Sensitivity of Photosynthesis¶

“…It involves an increased synthesis of D1 protein isoforms of PS II (28,29) and an increase of carotenoid synthesis (8). Overproduction of these components of the photosynthetic apparatus including carotenoids alleviated the negative effect of either high-light or UV-B radiation (7,30). In order to compare the protective effect of the carotenoid canthaxanthin on photosynthesis under oxidative stress to that of zeaxanthin, it was important to locate substantial amounts of canthaxanthin associated with the thylakoids and find a distribution in the three different types of membranes which roughly resembled the membrane distribution of zeaxanthin in the control strain (Table 1B).…”