Diurnal Pattern of Carbohydrates in Celery Leaves of Various Ages

Abstract

Diurnal fluctuations in soluble carbohydrates and starch were monitored in young (expanding), mature (first fully expanded), and old (nearing senescence) celery (Apium graveolens L.) leaves. In all tissues, mannitol and sucrose were the carbohydrates present in the highest concentrations. In old and young leaflets and their petioles, there was little change in levels of mannitol and sucrose in 26 hours. In mature leaflets, sucrose accumulated in the light and decreased in the dark; mannitol increased slightly in late afternoon. Starch concentration, although quite low, showed definite diurnal fluctuations in mature leaflets, but only small changes in young and old leaflets. Both sucrose and mannitol were present in mature petiole phloem tissues. Mannitol concentrations were high in the adjacent storage parenchyma tissue, but sucrose was almost undetectable. These data support earlier findings that sucrose is produced, translocated, and metabolized throughout the celery plant. Mannitol is also translocated, but also serves as a major storage carbohydrate in leaf tissues, especially petiole parenchyma. Starch serves as a minor short-term storage compound in leaflets.