Sources of Carbon for Export from Spinach Leaves throughout the Day

Document Type

Article

Publication Date

7-1-1989

Publication Source

Plant Physiology

Abstract

Rates of net carbon exchange, export, starch, and sucrose synthesis were measured in leaves of spinach (Spinacia oleracea L.) throughout a 14-hour period of sinusoidal light to determine the sources of carbon contributing to export. Net carbon exchange rate closely followed light level, but export remained relatively constant throughout the day. In the morning when photosynthesis was low, starch degradation provided most of the carbon for export, while accumulated sucrose was exported during the evening. At high photosynthesis rate, the regulatory metabolite fructose 2,6-bisphosphate was low, allowing more of the newly fixed carbon to flow to sucrose through cytosolic fructose bisphosphatase. When the rate of sucrose synthesis exceeded the rate of export from the leaf, sucrose accumulated and soon thereafter sucrose synthesis Dec.lined. A Dec.reasing sucrose synthesis rate resulted in additional carbon moving to the synthesis of starch, which was maintained throughout the remainder of the day. The Dec.lining sucrose synthesis rate coincided with Dec.reasing activity of sucrose phosphate synthase present in gel-filtered leaf extracts. A rise in the leaf levels of uridine diphosphoglucose and fructose 6-phosphate throughout the day was consistent with this Dec.lining activity.

Inclusive pages

1168-1174

ISBN/ISSN

0032-0889

Publisher

American Society of Plant Biologists

Volume

90

Peer Reviewed

yes

Keywords

steady-state labelling

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