Leaf Carbon Metabolism and Metabolite Levels during a Period of Sinusoidal Light 1
AUTOR(ES)
Servaites, Jerome C.
RESUMO
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.
ACESSO AO ARTIGO
http://www.pubmedcentral.nih.gov/articlerender.fcgi?artid=1055854Documentos Relacionados
- Regulation of Photosynthetic Carbon Metabolism in Cucumber by Light Intensity and Photosynthetic Period 1
- Carbon Dioxide and Water Vapor Exchange in the Crassulacean Acid Metabolism Plant Kalanchoë pinnáta during a Prolonged Light Period: METABOLIC AND STOMATAL CONTROL OF CARBON METABOLISM
- Photosynthesis, Carbohydrate Metabolism, and Export in Beta vulgaris L. and Phaseolus vulgaris L. during Square and Sinusoidal Light Regimes 1
- Influence of Leaf Age on Photosynthesis, Enzyme Activity, and Metabolite Levels in Wheat 1
- Carbon Dioxide Metabolism in Leaf Epidermal Tissue 1