Succinate Dehydrogenase and Other Respiratory Pathways in Thylakoid Membranes of Synechocystis sp. Strain PCC 6803: Capacity Comparisons and Physiological Function

Abstract

Respiration in cyanobacterial thylakoid membranes is interwoven with photosynthetic processes. We have constructed a range of mutants that are impaired in several combinations of respiratory and photosynthetic electron transport complexes and have examined the relative effects on the redox state of the plastoquinone (PQ) pool by using a quinone electrode. Succinate dehydrogenase has a major effect on the PQ redox poise, as mutants lacking this enzyme showed a much more oxidized PQ pool. Mutants lacking type I and II NAD(P)H dehydrogenases also had more oxidized PQ pools. However, in the mutant lacking type I NADPH dehydrogenase, succinate was essentially absent and effective respiratory electron donation to the PQ pool could be established after addition of 1 mM succinate. Therefore, lack of the type I NADPH dehydrogenase had an indirect effect on the PQ pool redox state. The electron donation capacity of succinate dehydrogenase was found to be an order of magnitude larger than that of type I and II NAD(P)H dehydrogenases. The reason for the oxidized PQ pool upon inactivation of type II NADH dehydrogenase may be related to the facts that the NAD pool in the cell is much smaller than that of NADP and that the NAD pool is fully reduced in the mutant without type II NADH dehydrogenase, thus causing regulatory inhibition. The results indicate that succinate dehydrogenase is the main respiratory electron transfer pathway into the PQ pool and that type I and II NAD(P)H dehydrogenases regulate the reduction level of NADP and NAD, which, in turn, affects respiratory electron flow through succinate dehydrogenase.

Transcriptional Regulation of the Respiratory Genes in the CyanobacteriumSynechocystissp. PCC 6803 during the Early Response to Glucose Feeding

“…As expected, 6-AN treatment significantly abolished the Glc induction of most of the respiratory genes as shown in Figure 5, indicating that NADPH production is a prerequisite for the expression of all the respiratory genes investigated in this study. NAD(P)H produced by Glc metabolism is oxidized by NDH-1 (Mi et al, 1992;Cooley and Vermaas, 2001) in both photosynthetic and cytoplasmic membranes, resulting in increase in the redox state of the plastoquinone (PQ) pool (Kujat and Owttrim, 2000). The reduced PQ is oxidized by CtaI and quinol oxidase (Cyd; Cooley and Vermaas, 2001).…”

“…NAD(P)H produced by Glc metabolism is oxidized by NDH-1 (Mi et al, 1992;Cooley and Vermaas, 2001) in both photosynthetic and cytoplasmic membranes, resulting in increase in the redox state of the plastoquinone (PQ) pool (Kujat and Owttrim, 2000). The reduced PQ is oxidized by CtaI and quinol oxidase (Cyd; Cooley and Vermaas, 2001). Thus, the redox status of the PQ pool can be modulated using inhibitors such as Hg 21 and CN 2 since they inhibit electron inputs into the PQ pool via NDH-1 and outputs from the CtaI to the molecular oxygen, respectively.…”

“…Simplified schemes depict the glycolytic, OPP, and TCA cycle pathways (A), and photosynthetic and respiratory electron transport (including ATP synthase; B) in the cyanobacterium Synechocystis. This scheme is derived from the data in Mi et al (1992), Howitt and Vermaas (1998), Howitt et al (1999), Cooley and Vermaas (2001), Yang et al (2002), Knowles and Plaxton (2003), Singh and Sherman (2005), Osanai et al (2007), and in the KEGG (www.genome.jp/kegg/ pathway.html) and CyanoBase (www.kazusa.or.jp/cyano/Synechocystis/ index.html) databases. Genes whose transcripts were increased 3.5-fold in abundance by Glc treatment are shown in italics.…”

“…To detect a Glc-induced increase in respiratory electron flow, we indirectly measured the redox state of the PQ pool in thylakoids by monitoring the chlorophyll (Chl) a fluorescence yield in darkness (Cooley et al, 2000;Cooley and Vermaas, 2001). As shown in Figure 6C, treatment of Synechocystis cells with the respiratory electron transport inhibitors KCN and 2,5-dibromo-3-methyl-6-isopropylbenzoquinone (DBMIB) caused the F o level to increase in a sigmoid manner, reaching a maximal level after 8 min with a half-life of 3.9 min.…”

Thylakoid Terminal Oxidases Are Essential for the CyanobacteriumSynechocystissp. PCC 6803 to Survive Rapidly Changing Light Intensities

“…In the model species Synechocystis sp. PCC 6803 (hereafter referred to as Synechocystis), plastoquinone is the electron acceptor from either PSII or one of several dehydrogenase complexes, which are linked to the oxidation of NADPH, NADH, or succinate (Cooley and Vermaas, 2001;Ohkawa et al, 2001). Electrons are transferred directly from plastoquinone to a cytochrome bd-quinol oxidase complex (Cyd), encoded by cydAB (Berry et al, 2002), or via cyt b 6 f and the soluble redox carriers to either PSI or an aa 3 -type cytochrome c oxidase complex (COX), encoded by ctaCIDIEI (Howitt and Vermaas, 1998; Fig.…”