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. 1989 Feb;89(2):403–408. doi: 10.1104/pp.89.2.403

Leaf Carbon Metabolism and Metabolite Levels during a Period of Sinusoidal Light 1

Jerome C Servaites 1,2, Donald R Geiger 1,2, Michelle A Tucci 1,2, Bernadette R Fondy 1,2
PMCID: PMC1055854  PMID: 16666556

Abstract

Photosynthesis rate, internal CO2 concentration, starch, sucrose, and metabolite levels were measured in leaves of sugar beet (Beta vulgaris L.) during a 14-h period of sinusoidal light, which simulated a natural light period. Photosynthesis rate closely followed increasing and decreasing light level. Chloroplast metabolite levels changed in a manner indicating differential activation of enzymes at different light levels. Starch levels declined during the first and last 2 hours of the photoperiod, but increased when photosynthesis rate was greater than 50% of maximal. Sucrose and sucrose phosphate synthase levels were constant during the photoperiod, which is consistent with a relatively steady rate of sucrose synthesis during the day as observed previously (BR Fondy et al. [1989] Plant Physiol 89: 396-402). When starch was being degraded, glucose 1-phosphate level was high and there was a large amount of glucose 6-phosphate above that in equilibrium with fructose 6-phosphate, while fructose 6-phosphate and triose-phosphate levels were very low. Likewise, the regulatory metabolite, fructose, 2,6-bisphosphate was high, indicating that little carbon could move to sucrose from starch by the triose-phosphate pathway. These data cast doubt upon the feasibility of significant carbon flow through the triose-phosphate pathway during starch degradation and support the need for an additional pathway for mobilizing starch carbon to sucrose.

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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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