Limits...
The RUBISCO to Photosystem II Ratio Limits the Maximum Photosynthetic Rate in Picocyanobacteria.

Zorz JK, Allanach JR, Murphy CD, Roodvoets MS, Campbell DA, Cockshutt AM - Life (Basel) (2015)

Bottom Line: Marine Synechococcus and Prochlorococcus are picocyanobacteria predominating in subtropical, oligotrophic marine environments, a niche predicted to expand with climate change.When grown under common low light conditions Synechococcus WH 8102 and Prochlorococcus MED 4 show similar Cytochrome b6f and Photosystem I contents normalized to Photosystem II content, while Prochlorococcus MIT 9313 has twice the Cytochrome b6f content and four times the Photosystem I content of the other strains.Photosystem II electron transport capacity is highly correlated to the molar ratio of RUBISCO active sites to Photosystem II but not to the ratio of cytochrome b6f to Photosystem II, nor to the ratio of Photosystem I: Photosystem II.

View Article: PubMed Central - PubMed

Affiliation: Department of Chemistry & Biochemistry, Mount Allison University, Sackville, New Brunswick, E4L 1G8, Canada. jkzorz@mta.ca.

ABSTRACT
Marine Synechococcus and Prochlorococcus are picocyanobacteria predominating in subtropical, oligotrophic marine environments, a niche predicted to expand with climate change. When grown under common low light conditions Synechococcus WH 8102 and Prochlorococcus MED 4 show similar Cytochrome b6f and Photosystem I contents normalized to Photosystem II content, while Prochlorococcus MIT 9313 has twice the Cytochrome b6f content and four times the Photosystem I content of the other strains. Interestingly, the Prochlorococcus strains contain only one third to one half of the RUBISCO catalytic subunits compared to the marine Synechococcus strain. The maximum Photosystem II electron transport rates were similar for the two Prochlorococcus strains but higher for the marine Synechococcus strain. Photosystem II electron transport capacity is highly correlated to the molar ratio of RUBISCO active sites to Photosystem II but not to the ratio of cytochrome b6f to Photosystem II, nor to the ratio of Photosystem I: Photosystem II. Thus, the catalytic capacity for the rate-limiting step of carbon fixation, the ultimate electron sink, appears to limit electron transport rates. The high abundance of Cytochrome b6f and Photosystem I in MIT 9313, combined with the slower flow of electrons away from Photosystem II and the relatively low level of RUBISCO, are consistent with cyclic electron flow around Photosystem I in this strain.

No MeSH data available.


Related in: MedlinePlus

Molar immunoquantitations of representative protein subunits PsbA (PSII); PsbD (PSII); PetC (Cytb6f complex); PsaC (PSI) and RbcL (RUBISCO large subunit) (a) Prochlorococcus MIT 9313; (b) Prochlorococcus MED 4; (c) Synechococcus WH8102. n = 6 independent determinations, ±95% confidence interval.
© Copyright Policy
Related In: Results  -  Collection

License
getmorefigures.php?uid=PMC4390859&req=5

life-05-00403-f002: Molar immunoquantitations of representative protein subunits PsbA (PSII); PsbD (PSII); PetC (Cytb6f complex); PsaC (PSI) and RbcL (RUBISCO large subunit) (a) Prochlorococcus MIT 9313; (b) Prochlorococcus MED 4; (c) Synechococcus WH8102. n = 6 independent determinations, ±95% confidence interval.

Mentions: Figure 2 presents the molar contents of representative proteins from PSI, PSII, the cytochrome b6f complex and RUBISCO in two Prochlorococcus strains, MIT 9313 and MED 4 and Synechococcus WH 8102 three to four days following subculturing. While these cultures are all monoalgal, they are not axenic, and harbour other bacteria, some of which may promote the growth of the picocyanobacterial cells [15]. For this reason caution must be taken in comparing absolute quantitations of proteins, as the fraction of the total protein isolated that derives from the cyanobacterial cells may vary with the extent of non-cyanobacterial bacteria in culture. As the photosynthetic proteins are only found in the cyanobacterial cells, we are able to confidently report the molar stoichiometries of the protein complexes (see Table 1). The three picocyanobacterial strains have remarkably different photosynthetic apparatus stoichiometries despite being grown under common conditions. When normalized to the PsbA proxy for PSII content, the PSU stoichiometry (PSII:Cytb6f:PSI:RUBISCO) is 1:2.5:9.0:0.5 for MIT 9313; 1:1.3:2.0:0.8 for MED 4; and 1:1.1:2.3:1.5 for WH 8102. Thus, under these conditions, MIT 9313 devotes relatively more resources to the transport of electrons away from PSII or around PSI, and less to RUBISCO, which catalyzes the limiting step in the ultimate transfer of those electrons to fix carbon. This suggests that MIT 9313 uses photosynthesis rate less for carbon fixation and more for ATP generation through cyclic electron flow around PSI than the other strains. It should also be noted from Figure 1 that this increased allocation to cytochrome b6f and PSI occurs as the cells enter their phase of most rapid growth and decreases as division slows in older cultures. Overall, the highlight ecotype of Prochlorococcus (MED 4) has a PSU stoichiometry more similar to the marine Synechococcus strain than to the low light Prochlorococcus strain (MIT 9313). The exception is the ratio of RUBISCO to PSII where the Prochlorococcus strains both have significantly (p < 0.0001, one way ANOVA with Tukey’s post-test) less RUBISCO per PSII than does the marine Synechococcus.


The RUBISCO to Photosystem II Ratio Limits the Maximum Photosynthetic Rate in Picocyanobacteria.

Zorz JK, Allanach JR, Murphy CD, Roodvoets MS, Campbell DA, Cockshutt AM - Life (Basel) (2015)

Molar immunoquantitations of representative protein subunits PsbA (PSII); PsbD (PSII); PetC (Cytb6f complex); PsaC (PSI) and RbcL (RUBISCO large subunit) (a) Prochlorococcus MIT 9313; (b) Prochlorococcus MED 4; (c) Synechococcus WH8102. n = 6 independent determinations, ±95% confidence interval.
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4390859&req=5

life-05-00403-f002: Molar immunoquantitations of representative protein subunits PsbA (PSII); PsbD (PSII); PetC (Cytb6f complex); PsaC (PSI) and RbcL (RUBISCO large subunit) (a) Prochlorococcus MIT 9313; (b) Prochlorococcus MED 4; (c) Synechococcus WH8102. n = 6 independent determinations, ±95% confidence interval.
Mentions: Figure 2 presents the molar contents of representative proteins from PSI, PSII, the cytochrome b6f complex and RUBISCO in two Prochlorococcus strains, MIT 9313 and MED 4 and Synechococcus WH 8102 three to four days following subculturing. While these cultures are all monoalgal, they are not axenic, and harbour other bacteria, some of which may promote the growth of the picocyanobacterial cells [15]. For this reason caution must be taken in comparing absolute quantitations of proteins, as the fraction of the total protein isolated that derives from the cyanobacterial cells may vary with the extent of non-cyanobacterial bacteria in culture. As the photosynthetic proteins are only found in the cyanobacterial cells, we are able to confidently report the molar stoichiometries of the protein complexes (see Table 1). The three picocyanobacterial strains have remarkably different photosynthetic apparatus stoichiometries despite being grown under common conditions. When normalized to the PsbA proxy for PSII content, the PSU stoichiometry (PSII:Cytb6f:PSI:RUBISCO) is 1:2.5:9.0:0.5 for MIT 9313; 1:1.3:2.0:0.8 for MED 4; and 1:1.1:2.3:1.5 for WH 8102. Thus, under these conditions, MIT 9313 devotes relatively more resources to the transport of electrons away from PSII or around PSI, and less to RUBISCO, which catalyzes the limiting step in the ultimate transfer of those electrons to fix carbon. This suggests that MIT 9313 uses photosynthesis rate less for carbon fixation and more for ATP generation through cyclic electron flow around PSI than the other strains. It should also be noted from Figure 1 that this increased allocation to cytochrome b6f and PSI occurs as the cells enter their phase of most rapid growth and decreases as division slows in older cultures. Overall, the highlight ecotype of Prochlorococcus (MED 4) has a PSU stoichiometry more similar to the marine Synechococcus strain than to the low light Prochlorococcus strain (MIT 9313). The exception is the ratio of RUBISCO to PSII where the Prochlorococcus strains both have significantly (p < 0.0001, one way ANOVA with Tukey’s post-test) less RUBISCO per PSII than does the marine Synechococcus.

Bottom Line: Marine Synechococcus and Prochlorococcus are picocyanobacteria predominating in subtropical, oligotrophic marine environments, a niche predicted to expand with climate change.When grown under common low light conditions Synechococcus WH 8102 and Prochlorococcus MED 4 show similar Cytochrome b6f and Photosystem I contents normalized to Photosystem II content, while Prochlorococcus MIT 9313 has twice the Cytochrome b6f content and four times the Photosystem I content of the other strains.Photosystem II electron transport capacity is highly correlated to the molar ratio of RUBISCO active sites to Photosystem II but not to the ratio of cytochrome b6f to Photosystem II, nor to the ratio of Photosystem I: Photosystem II.

View Article: PubMed Central - PubMed

Affiliation: Department of Chemistry & Biochemistry, Mount Allison University, Sackville, New Brunswick, E4L 1G8, Canada. jkzorz@mta.ca.

ABSTRACT
Marine Synechococcus and Prochlorococcus are picocyanobacteria predominating in subtropical, oligotrophic marine environments, a niche predicted to expand with climate change. When grown under common low light conditions Synechococcus WH 8102 and Prochlorococcus MED 4 show similar Cytochrome b6f and Photosystem I contents normalized to Photosystem II content, while Prochlorococcus MIT 9313 has twice the Cytochrome b6f content and four times the Photosystem I content of the other strains. Interestingly, the Prochlorococcus strains contain only one third to one half of the RUBISCO catalytic subunits compared to the marine Synechococcus strain. The maximum Photosystem II electron transport rates were similar for the two Prochlorococcus strains but higher for the marine Synechococcus strain. Photosystem II electron transport capacity is highly correlated to the molar ratio of RUBISCO active sites to Photosystem II but not to the ratio of cytochrome b6f to Photosystem II, nor to the ratio of Photosystem I: Photosystem II. Thus, the catalytic capacity for the rate-limiting step of carbon fixation, the ultimate electron sink, appears to limit electron transport rates. The high abundance of Cytochrome b6f and Photosystem I in MIT 9313, combined with the slower flow of electrons away from Photosystem II and the relatively low level of RUBISCO, are consistent with cyclic electron flow around Photosystem I in this strain.

No MeSH data available.


Related in: MedlinePlus