Characterization of Glucose-6-Phosphate Incorporation into Starch by Isolated Intact Cauliflower-Bud Plastids.

AUTOR(ES)
RESUMO

Intact plastids from cauliflower (Brassica oleracea var Prince de Bretagne) buds were isolated according to the method described by Journet and Douce (E.P. Journet and R. Douce [1985] Plant Physiol 79: 458-467). Incubation of these plastids with various 14C-labeled compounds revealed that glucose-6-phosphate can act as a precursor for starch synthesis. However, significant rates (incorporation of 120 nmol glucose mg-1 protein h-1) could only be observed when both 3-phosphoglyceric acid and ATP were present as well. Starch synthesis in isolated plastids was strongly dependent upon the intactness of the organelle. The presence of a high-affinity ATP/ADP translocator with a Km for ATP of 12 [mu]M was demonstrated by uptake experiments with [14C]ATP. ADP inhibited both ATP uptake and effector-stimulated starch synthesis. Effector-stimulated glucose-6-phosphate-dependent starch synthesis was not significantly influenced by fructose-6-phosphate or 2-deoxyglucose-6-phosphate but was strongly inhibited by triose phosphate and inorganic phosphate. Starch synthesis was also inhibited by 4,4[prime]-diisothio-cyanostilbene-2,2[prime]-disulfonate, which is known to be a potent inhibitor of the chloroplast phosphate translocator. The data presented here support the view that starch biosynthesis in heterotrophic tissues is powered by increasing levels of cytosolic 3-phosphoglyceric acid and ATP when glucose-6-phosphate is available.

ACESSO AO ARTIGO

Documentos Relacionados