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

(a) Electron Transport Capacity away from Photosystem II 1/τ2 (e− PSII−1 s−1) plotted versus maximum Electron Transport Rate for Photosystem II under saturating light (e− PSII−1 s−1); each point represents a paired measurement of the two parameters on an independent culture. Prochlorococcus MIT 9313: blue triangles; Prochlorococcus MED 4: green circles; Synechococcus WH8102: red squares. Line shows linear regression through the pooled points from all three strains; R2 = 0.89, dotted lines show 95% confidence interval on the pooled regression; (b) Electron Transport Capacity away from Photosystem II 1/τ2 (e− PSII−1 s−1) (n = 3–6 independent determinations, ±95% confidence interval on the y-axis) plotted versus the ratio of Cytb6f: PSII (n = 6 independent determinations, ±95% confidence interval on the x-axis);(c) Electron Transport Capacity away from Photosystem II 1/τ2 (e− PSII−1 s−1) (n = 3–6 independent determinations, ±95% confidence interval on the y-axis) plotted versus the ratio of Cytb6f : PSI (n = 6 independent determinations, ±95% confidence interval on the x-axis); (d) Electron Transport Capacity away from Photosystem II 1/τ2 (e− PSII−1 s−1) (n = 3–6 independent determinations, ± 95% confidence interval on the y-axis) plotted versus the ratio of PSI: PSII (n = 6 independent determinations, ±95% confidence interval on the x-axis); (e) Electron Transport Capacity away from Photosystem II 1/τ2 (e− PSII−1 s−1) (n = 3–6 independent determinations, ± 95% confidence interval on the y-axis) plotted versus the ratio of RUBISCO: PSII (n = 6 independent determinations, ±95% confidence interval). Line shows linear regression; R2 = 0.99, dotted lines show 95% confidence interval on the pooled regression.
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life-05-00403-f004: (a) Electron Transport Capacity away from Photosystem II 1/τ2 (e− PSII−1 s−1) plotted versus maximum Electron Transport Rate for Photosystem II under saturating light (e− PSII−1 s−1); each point represents a paired measurement of the two parameters on an independent culture. Prochlorococcus MIT 9313: blue triangles; Prochlorococcus MED 4: green circles; Synechococcus WH8102: red squares. Line shows linear regression through the pooled points from all three strains; R2 = 0.89, dotted lines show 95% confidence interval on the pooled regression; (b) Electron Transport Capacity away from Photosystem II 1/τ2 (e− PSII−1 s−1) (n = 3–6 independent determinations, ±95% confidence interval on the y-axis) plotted versus the ratio of Cytb6f: PSII (n = 6 independent determinations, ±95% confidence interval on the x-axis);(c) Electron Transport Capacity away from Photosystem II 1/τ2 (e− PSII−1 s−1) (n = 3–6 independent determinations, ±95% confidence interval on the y-axis) plotted versus the ratio of Cytb6f : PSI (n = 6 independent determinations, ±95% confidence interval on the x-axis); (d) Electron Transport Capacity away from Photosystem II 1/τ2 (e− PSII−1 s−1) (n = 3–6 independent determinations, ± 95% confidence interval on the y-axis) plotted versus the ratio of PSI: PSII (n = 6 independent determinations, ±95% confidence interval on the x-axis); (e) Electron Transport Capacity away from Photosystem II 1/τ2 (e− PSII−1 s−1) (n = 3–6 independent determinations, ± 95% confidence interval on the y-axis) plotted versus the ratio of RUBISCO: PSII (n = 6 independent determinations, ±95% confidence interval). Line shows linear regression; R2 = 0.99, dotted lines show 95% confidence interval on the pooled regression.

Mentions: To determine a mechanistic basis for the differences in photosynthetic electron transport we plot the capacity for electron transport away from PSII (ETR capacity) versus other measured parameters (Figure 4). As expected, the ETR capacity is strongly correlated to ETRmax, the electron transport rate under saturating light, with an R2 of 0.89 (Figure 4A). ETR capacity is not correlated to the molar ratio of cytochrome b6f to PSII (Figure 4B), nor to the molar ratio of cytochrome b6f to PSI (Figure 4C) nor to the ratio of PSI to PSII (Figure 4D). This indicates that the capacity for electron transport away from PSII is not directly limited by the available pool of cytochrome b6f complexes serving PSII or PSI, nor by the pool of PSI extracting electrons from the inter-system electron transport chain. In fact, the strain with the lowest ratio of cytochrome b6f to PSII shows the highest rate of electron transport away from PSII. ETR capacity is, however, strongly correlated to the ratio of RUBISCO active sites (measured RbcL subunits) to PSII, with an R2 of 0.83 across the three strains (Figure 4E).


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)

(a) Electron Transport Capacity away from Photosystem II 1/τ2 (e− PSII−1 s−1) plotted versus maximum Electron Transport Rate for Photosystem II under saturating light (e− PSII−1 s−1); each point represents a paired measurement of the two parameters on an independent culture. Prochlorococcus MIT 9313: blue triangles; Prochlorococcus MED 4: green circles; Synechococcus WH8102: red squares. Line shows linear regression through the pooled points from all three strains; R2 = 0.89, dotted lines show 95% confidence interval on the pooled regression; (b) Electron Transport Capacity away from Photosystem II 1/τ2 (e− PSII−1 s−1) (n = 3–6 independent determinations, ±95% confidence interval on the y-axis) plotted versus the ratio of Cytb6f: PSII (n = 6 independent determinations, ±95% confidence interval on the x-axis);(c) Electron Transport Capacity away from Photosystem II 1/τ2 (e− PSII−1 s−1) (n = 3–6 independent determinations, ±95% confidence interval on the y-axis) plotted versus the ratio of Cytb6f : PSI (n = 6 independent determinations, ±95% confidence interval on the x-axis); (d) Electron Transport Capacity away from Photosystem II 1/τ2 (e− PSII−1 s−1) (n = 3–6 independent determinations, ± 95% confidence interval on the y-axis) plotted versus the ratio of PSI: PSII (n = 6 independent determinations, ±95% confidence interval on the x-axis); (e) Electron Transport Capacity away from Photosystem II 1/τ2 (e− PSII−1 s−1) (n = 3–6 independent determinations, ± 95% confidence interval on the y-axis) plotted versus the ratio of RUBISCO: PSII (n = 6 independent determinations, ±95% confidence interval). Line shows linear regression; R2 = 0.99, dotted lines show 95% confidence interval on the pooled regression.
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Related In: Results  -  Collection

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Show All Figures
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life-05-00403-f004: (a) Electron Transport Capacity away from Photosystem II 1/τ2 (e− PSII−1 s−1) plotted versus maximum Electron Transport Rate for Photosystem II under saturating light (e− PSII−1 s−1); each point represents a paired measurement of the two parameters on an independent culture. Prochlorococcus MIT 9313: blue triangles; Prochlorococcus MED 4: green circles; Synechococcus WH8102: red squares. Line shows linear regression through the pooled points from all three strains; R2 = 0.89, dotted lines show 95% confidence interval on the pooled regression; (b) Electron Transport Capacity away from Photosystem II 1/τ2 (e− PSII−1 s−1) (n = 3–6 independent determinations, ±95% confidence interval on the y-axis) plotted versus the ratio of Cytb6f: PSII (n = 6 independent determinations, ±95% confidence interval on the x-axis);(c) Electron Transport Capacity away from Photosystem II 1/τ2 (e− PSII−1 s−1) (n = 3–6 independent determinations, ±95% confidence interval on the y-axis) plotted versus the ratio of Cytb6f : PSI (n = 6 independent determinations, ±95% confidence interval on the x-axis); (d) Electron Transport Capacity away from Photosystem II 1/τ2 (e− PSII−1 s−1) (n = 3–6 independent determinations, ± 95% confidence interval on the y-axis) plotted versus the ratio of PSI: PSII (n = 6 independent determinations, ±95% confidence interval on the x-axis); (e) Electron Transport Capacity away from Photosystem II 1/τ2 (e− PSII−1 s−1) (n = 3–6 independent determinations, ± 95% confidence interval on the y-axis) plotted versus the ratio of RUBISCO: PSII (n = 6 independent determinations, ±95% confidence interval). Line shows linear regression; R2 = 0.99, dotted lines show 95% confidence interval on the pooled regression.
Mentions: To determine a mechanistic basis for the differences in photosynthetic electron transport we plot the capacity for electron transport away from PSII (ETR capacity) versus other measured parameters (Figure 4). As expected, the ETR capacity is strongly correlated to ETRmax, the electron transport rate under saturating light, with an R2 of 0.89 (Figure 4A). ETR capacity is not correlated to the molar ratio of cytochrome b6f to PSII (Figure 4B), nor to the molar ratio of cytochrome b6f to PSI (Figure 4C) nor to the ratio of PSI to PSII (Figure 4D). This indicates that the capacity for electron transport away from PSII is not directly limited by the available pool of cytochrome b6f complexes serving PSII or PSI, nor by the pool of PSI extracting electrons from the inter-system electron transport chain. In fact, the strain with the lowest ratio of cytochrome b6f to PSII shows the highest rate of electron transport away from PSII. ETR capacity is, however, strongly correlated to the ratio of RUBISCO active sites (measured RbcL subunits) to PSII, with an R2 of 0.83 across the three strains (Figure 4E).

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