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. 1987 Jun;84(2):549–554. doi: 10.1104/pp.84.2.549

Changes in Levels of Intermediates of the C4 Cycle and Reductive Pentose Phosphate Pathway under Various Light Intensities in Maize Leaves 1

Hideaki Usuda 1
PMCID: PMC1056618  PMID: 16665477

Abstract

The rate of CO2 assimilation and levels of metabolites of the C4 cycle and reductive pentose phosphate pathway in attached leaves of maize (Zea mays L.) were measured over a range of light intensity from 0 to 1,900 microEinsteins per square meter per second under a saturated CO2 concentration of 350 microliters per liter and a limiting CO2 concentration of 133 microliters per liter. The level of ribulose 1,5-bisphosphate (RuBP) stayed almost constant (around 60 nanomoles per milligram chlorophyll [Chl]) from low to high light intensities under 350 microliters per liter. Levels of 3-phosphoglycerate (PGA) increased from 100 to 650 nanomoles per milligram Chl under 350 microliters per liter CO2 with increasing light intensity. The calculated RuBP concentration of 6 millimolar (corresponded to 60 nanomoles per milligram Chl) was about two times above the estimated RuBP binding-site concentration on ribulose bisphosphate carboxylase-oxygenase (Rubisco) of ∼2.6 millimolar in maize bundle sheath chloroplasts in the light. The ratio of RuBP/PGA increased with decreasing light intensity under 350 microliters per liter CO2. These results suggest that RuBP carboxylation is under control of light intensity possibly due to a limited supply of CO2 to Rubisco through the C4 cycle whose activity is highly dependent on light intensity. Pyruvate level increased with increasing light intensity as long as photosynthesis rate increased. A positive relationship between levels of PGA and those of pyruvate during steady-state photosynthesis under various conditions suggests that an elevated concentration of PGA increases the carbon input into the C4 cycle through the conversion of PGA to PEP and consequently the level of total intermediates of the C4 cycle can be raised to mediate higher photosynthesis rate.

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Selected References

These references are in PubMed. This may not be the complete list of references from this article.

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