They do not contain chloroplasts. Instead, the entire cell acts as a sort of thylakoid. The cyanobacterium has an outer cell wall, cell membrane, and thylakoid membrane. Inside this membrane is the bacterial DNA, cytoplasm, and carboxysomes. The thylakoid membrane has functional electron transfer chains that support photosynthesis and cellular respiration. Cyanobacteria thylakoid membranes don't form grana and stroma. Instead, the membrane forms parallel sheets near the cytoplasmic membrane, with enough space between each sheet for phcobilisomes, the light harvesting structures.
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Mott KA, Sibbernsen ED, Shope JC 2008. The role of the mesophyll in stomatal responses to light and CO2. Plant, Cell and Environment 31: 1299–1305.
Role of coupling factor ATPase in energy conversion as revealed by ..
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Although the role of the guard cell chloroplast in stomatal function is still unclear, it is apparent that substantial photosynthetic electron transport and functional Calvin cycle activity takes place within guard cells, although their contributions to stomatal responses has not been resolved. Transgenic plants with impairments in components of electron transport and down stream processes have and continue to provide an ideal opportunity to explore some of the unanswered questions regarding the link between both mesophyll and guard cell photosynthesis and stomatal function as well as providing key information on stomatal responses and mechanisms to changing environmental parameters. The advancement of in situ techniques and the production of mutant and transgenic plants along with the identification of gene trap lines, guard cell specific promoters and single cell transcriptomics is providing new opportunities to address many of the questions that remain regarding guard cell chloroplast function, guard cell metabolism and signalling pathways that enable stomata and photosynthesis to be in tune with each other and the environment.
During photosynthesis in plants, ..
Lawson T, Oxborough K, Morison JIL, Baker NR. 2003. The response of guard cell photosynthesis to CO2, O2, light and water stress in a range of species are similar. Journal of Experimental Botany 54: 1734–1752.
Simplified model of F O F 1-ATPase alias ATP synthase of E
Messinger SM, Buckley TN, Mott KA. 2006. Evidence for involvement of photosynthetic processes in the stomatal response to CO2. Plant Physiology 140: 771–778.
Cellular Respiration (Krebs Cycle) - The Biology Corner
Lawson T, Lefebvre S, Baker NR, Morison JIL, Raines C. 2008. Reductions in mesophyll and guard cell photosynthesis impact on the control of stomatal responses to light and CO2. Journal of Experimental Botany. 59: 3609–3619.
Where does cellular respiration occur within the cell
The link between photosynthetic CO2demand and stomatal behaviour has often been considered to be guard cell sensing of Ci or the Ci/Ca ratio. However as described above, transgenic plants with elevated Ci concentrations show no differences in stomatal conductance compared with wild type controls, questioning not only the role of Ci linking mesophyll photosynthesis with stomatal behaviour, but whether stomata respond to internal or external CO2 concentration (von Caemmerer et al. 2004). Alternatively, it has been proposed that guard cells sense the metabolic status of mesophyll via a diffusible factor that is a product of mesophyll photosynthetic activity, such as ATP, NADPH or an unknown substance which was named stomatin by Lee & Bowling (1992). The balance between electron transport and carboxylation reactions has also been postulated as a possible mechanism (see Messinger et al. 2006). However, studies on transgenic plants with impaired photosynthetic rates have demonstrated that stomatal opening is not influenced by photosynthesis alone, and therefore support the conclusion that neither guard nor mesophyll cell photosynthesis are essential for stomatal function and therefore do not support a mesophyll or Ci driven signal. More recently, Mott et al. (2008) demonstrated mesophyll influences on stomatal behaviour, by grafting isolated peels onto mesophyll and showed stomatal responses to light and CO2. These results led Mott and co-workers to renew the suggestion that stomata respond to a signal generated in mesophyll in response to changes in light and CO2. Mesophyll photosynthetic sucrose accumulated in the guard cell apoplast has also been hypothesized as the signal that links stomatal aperture with mesophyll photosynthesis (Outlaw and De Vlieghere, 2001).