Photosynthesis and photorespiration of marine angiosperms.
and photorespiration of marine angiosperms.
The quantum efficiency of photosynthesis in macroalgae …
The main difference between a lifeless clump of chemicals, and a living life form, composed of the same chemicals, is; Information and access to an energy source. The word science comes from a Latin word scientica, which means knowledge, or information. Science is a process of systematically gathering detailed information and gaining exact knowledge. That vital information includes; how the basic elements are organized and how they utilize energy. We do not know all the "life" information secrets but we are learning more every day.
The advantage that comes from this two-stage process is that the active pumping of carbon into the bundle sheath cell and the blocking of oxygen produce an environment with 10-120x as much CO2 available to the Calvin cycle and the tends to be optimally utilized. The high CO2 concentration and the absence of oxygen implies that the system never experiences the detractive effects of .
photosynthesis, photorespiration and respiration
The drawback to C4 photosynthesis is the extra energy in the form of that is used to pump the 4-carbon acids to the bundle sheath cell and the pumping of the 3-carbon compound back to the mesophyll cell for conversion to PEP. This loss to the system is why C3 plants will outperform C4 plants if there is a lot of water and sun. The C4 plants make some of that energy back in the fact that the rubisco is optimally used and the plant has to spend less energy synthesizing rubisco.
These intermediates are characterized by their resistance to so that they can operate in higher temperatures and dryer environments than . At right, the ranges of CO2 compensation points for the three types of plants are shown. These compensation points are the values at which the plants cease to provide net photosynthesis.
Effects of pH on seagrass photosynthesis: a laboratory and field ..
Udotea flabellum is a marine, macroscopic green alga with C4-like photosynthetic characteristics, including little O2 inhibition of photosynthesis, a low CO2 compensation point, and minimal photorespiration; but it lacks anatomical features analogous to the Kranz compartmentation of C4 plants, and phosphoenolpyruvate carboxylase [PEPC; orthophosphate:oxaloacetate carboxy-lyase (phosphorylating), EC 188.8.131.52] activity is negligible. Phosphoenolpyruvate carboxykinase (PEPCK) activity (carboxylating) in Udotea extracts was equivalent to that of ribulose-bisphosphate carboxylase [Rubisco; 3-phospho-D-glycerate carboxy-lyase (dimerizing), EC 184.108.40.206]. When PEPCK activity was inhibited in vivo with 3-mercaptopicolinic acid (MPA), thallus photosynthesis decreased by 70% and became sensitive to O2. Codium decorticatum, a related species that lacks C4-like photosynthetic features and PEPCK activity, showed no increase in O2 inhibition upon exposure to MPA. Rubisco and PEPC activities in Udotea were not inhibited by MPA. Labeling of the early photosynthetic products malate and aspartate was reduced 66% by MPA, while intermediates of the photorespiratory carbon oxidation cycle showed a 3-fold increase. Udotea evolved O2 in the light in the absence of inorganic carbon, suggesting it had an endogenous carbon source for photosynthesis. Exogenous malate stimulated this process, while MPA inhibited it. PEPCK was not involved in Crassulacean acid metabolism or dark CO2 fixation. These MPA studies establish a direct link between PEPCK activity and the low O2 inhibition of photosynthesis and low photorespiration in Udotea. The data are consistent with carboxylation by a cytosolic PEPCK providing a C4 acid, such as malate, to the chloroplast for decarboxylation to elevate the CO2 concentration at the Rubisco fixation site. Udotea is to date the most primitive plant with a C4-like form of photosynthesis.
Photorespiration, the rate of which is directly related to the O2/CO2 ratio, due to the dual function of Rubisco, may be an important mechanism in maintaining the limits of O2 and CO2 concentrations by restricting land plant productivity and weathering.
photorespiration in marine angiosperms.
Photorespiration and C4 Plants - Biology Pages
The marine angiosperms, or seagrasses, constitute a small but important plant group, common to many coastal habitats
Photorespiration and C4 Plants ..
Over 8000 species of angiosperms have developed ..
Journal of Integrative Plant Biology ..
Photorespiration and Carbon Limitation Determine ..
The acidity was found to arise from the opening of their stomata at night to take in CO2 and fix it into malic acid for storage in the large vacuoles of their photosynthetic cells. It could drop the pH to 4 with a malic acid concentration up to 0.3M . Then in the heat of the day, the stomata close tightly to conserve water and the malic acid is decarboxylated to release the CO2 for fixing by the Calvin cycle. PEP is used for the initial short-term carbon fixation as in the , but the entire chain of reactions occurs in the same cell rather than handing off to a separate cell as with the C4 plants. In the CAM strategy, the processes are separated temporally, the initial CO2 fixation at night, and the malic acid to Calvin cycle part taking place during the day.
Carbon Limitation Determine Productivity in Temperate ..
Respiration refers to the metabolism of oxygen and the release of carbon dioxide. In it is a positive term, a process vital to life. But photorespiration is an entirely negative term because it represents a severe loss to the process of using light energy in photosynthetic organisms to fix carbon for subsequent carbohydrate synthesis. By leading to the loss of up to half of the carbon that has been fixed at the expense of light energy, photorespiration undoes the work of photosynthesis.
and photorespiration in marine angiosperms.
The connection to hot and dry conditions comes from the fact that all the plants will close their stomata in hot and dry weather to conserve moisture, and the continuing fixation of carbon from the air drops the CO2 dramatically from the atmospheric concentration of nominally 380 ppm (2004 value). If the CO2 compensation point is lower on the above scale, the plant can operate in hotter and dryer conditions. The limits are placed by the fact that begins to fix oxygen rather than CO2, undoing the work of photosynthesis. C4 plants shield their rubisco from the oxygen, so can operate all the way down to essentially zero CO2 without the onset of photorespiration.
Figure 4 from Seagrass Respiration An assessment of …
Photorespiration happens in when the CO2 concentration drops to about 50 ppm. The key enzyme that accomplishes the fixing of carbon is , and at low concentrations of CO2 it begins to fix oxygen instead.
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