Regulation of Carbon Partitioning in Source and Sink Leaf Parts in Sweet Pepper (Capsicum annuum L.) Plants : Role of Fructose 2,6-Bisphosphate.

Area expansion rate, partitioning of photosynthetically fixed carbon, and levels of fructose 2,6-bisphosphate (fru-2,6-P(2)) were determined in individual parts of developing leaves of sweet pepper (Capsicum annuum L.). The base was rapidly expanding and allocated less carbon to sucrose synthesis in comparison to the leaf tip, where expansion had almost stopped. The change in leaf expansion rate and carbon partitioning happened gradually. During day time levels of fru-2,6-P(2) were consistently higher in the leaf base than in the leaf tip. Leaf expansion rate and carbon partitioning were closely related to day time levels of fru-2,6-P(2), suggesting that fru-2,6-P(2) is an important factor in adjustment of metabolism during sink-to-source transition of leaf tissue. The levels of fru-2,6-P(2) changed markedly after a dark-to-light transition in the leaf base, but not in the leaf tip, suggesting that regulatory systems based on fru-2,6-P(2) are different in sink and source leaf tissue. During the period upon dark-to-light transition the variations in level of fru-2,6-P(2) did not show a close correlation to changes in the carbon partitioning, until the metabolism had reached a steady state.