The influence of inorganic phosphate on photosynthesis …

Actually, photosynthesis is not a single process, but two, each with multiple steps.

Phosphate transients in photosynthesis*1 - ResearchGate

N2 - Intact chloroplasts were obtained from mesophyll protoplasts isolated from Mesembryanthemum crystallinum in the C3 or Crassulacean acid metabolism (CAM) photosynthetic mode, and examined for the influence of inorganic phosphate (Pi) on aspects of bicarbonate-dependent O2 evolution and CO2 fixation. While the chloroplasts from both modes responded similarly to varying Pi, some features appear typical of chloroplasts from species capable of CAM, including a relatively high capacity for photosynthesis in the absence of Pi, a short induction period, and resistance to inhibition of photosynthesis by high levels of Pi. In the absence of Pi the chloroplasts retained 75-85% of the 14CO2 fixed and the total export of dihydroxyacetone phosphate was low compared with the rate of photosynthesis. In CAM plants the ability to conduct photosynthesis and retain most of the fixed carbon in the chloroplasts at low external Pi concentrations may enable storage of carbohydrates which are essential for providing a carbon source for the nocturnal synthesis of malic acid. At high external Pi concentrations (e.g. 10 25 mM), the amount of total dihydroxyacetone phosphate exported to the assay medium relative to the rate of photosynthesis was high while the products of 14CO2 fixation were largely retained in the chloroplasts which indicates starch degradation is occurring at high Pi levels. Starch degradation normally occurs in CAM plants in the dark; high levels of Pi may induce starch degradation in the light which has the effect of limiting export of the immediate products of photosynthesis and thus the degree of Pi inhibition of photosynthesis with the isolated chloroplast.

Learn how plants harness the sun's energy using photosynthesis, and the factors which affect this process.

PHOSPHATE TRANSIENTS IN PHOTOSYNTHESIS

By definition, .

The process of photosynthesis uses raw materials like carbon dioxide, water, and solar energy to produce oxygen and carbohydrates.

This germination is followed closely by the beginning of the photosynthetic process which we have been studying.

AB - Intact chloroplasts were obtained from mesophyll protoplasts isolated from Mesembryanthemum crystallinum in the C3 or Crassulacean acid metabolism (CAM) photosynthetic mode, and examined for the influence of inorganic phosphate (Pi) on aspects of bicarbonate-dependent O2 evolution and CO2 fixation. While the chloroplasts from both modes responded similarly to varying Pi, some features appear typical of chloroplasts from species capable of CAM, including a relatively high capacity for photosynthesis in the absence of Pi, a short induction period, and resistance to inhibition of photosynthesis by high levels of Pi. In the absence of Pi the chloroplasts retained 75-85% of the 14CO2 fixed and the total export of dihydroxyacetone phosphate was low compared with the rate of photosynthesis. In CAM plants the ability to conduct photosynthesis and retain most of the fixed carbon in the chloroplasts at low external Pi concentrations may enable storage of carbohydrates which are essential for providing a carbon source for the nocturnal synthesis of malic acid. At high external Pi concentrations (e.g. 10 25 mM), the amount of total dihydroxyacetone phosphate exported to the assay medium relative to the rate of photosynthesis was high while the products of 14CO2 fixation were largely retained in the chloroplasts which indicates starch degradation is occurring at high Pi levels. Starch degradation normally occurs in CAM plants in the dark; high levels of Pi may induce starch degradation in the light which has the effect of limiting export of the immediate products of photosynthesis and thus the degree of Pi inhibition of photosynthesis with the isolated chloroplast.

This step requires ample sunlight for the process and hence it is termed as the light-dependent phase of photosynthesis.


Photosynthesis Questions - Download as Word ..

The inner chloroplast membrane have a specific antiporter thatcatalyzes the one-for-one exchange of Pi with a triosephosphate, either dihydroxyacetone phosphate or 3-phosphoglycerate (Fig. 18–7).This antiporter simultaneously moves Pi into the chloroplast, where it is usedin photophosphorylation, and moves triose phosphate into the cytosol, where itcan be used to synthesize sucrose, the form in which the fixed carbon istransported to distant plant tissues. Sucrose synthesis in the cytosol andstarch synthesis in the chloroplast are the major pathways by which the excesstriose phosphate from photosynthesis is “harvested.” Sucrose synthesis releasesfour Pi molecules from the four triose phosphates requiredfor its production. For every molecule of triosephosphate removed from the chloroplast, one Pi is transportedinto the chloroplast, providing the ninth Pi mentionedabove, to be used in regenerating ATP. If this exchangewere blocked, triose phosphate synthesis wouldquickly deplete the available Pi in the chloroplast, slowingATP synthesis and suppressing assimilation of CO2into starch.

Triose phosphate Hexose ADP Reduced ..

So how can these factors have an effect on the rate of photosynthesis? Lets start off with the light intensity. When the light intensity is poor, there is a shortage of ATP and NADPH, as these are products from the light dependent reactions. Without these products the light independent reactions can't occur as glycerate 3-phosphate cannot be reduced. Therefore a shortage of these products will limit the rate of photosynthesis. When the carbon dioxide concentration is low, the amount of glycerate 3-phosphate produced is limited as carbon dioxide is needed for its production and therefore the rate of photosynthesis is affected. Finally, many enzymes are involved during the process of photosynthesis. At low temperatures these enzymes work slower. At high temperatures the enzymes no longer work effectively. This affects the rate of the reactions in the Calvin cycle and therefore the rate of photosynthesis will be affected.

Photosynthesis | Essays in Biochemistry

FIGURE 18–7 The Pi–triose phosphate antiport system of the innerchloroplast membrane. This transporter facilitates the exchange ofcytosolic Pi for stromal dihydroxyacetone phosphate. The products ofphotosynthetic carbon assimilation are thus moved into the cytosolwhere they serve as a starting point for sucrose biosynthesis, and Pirequired for photophosphorylation is moved into the stroma.