Plant growth involves the coordinated distribution of carbon resources both towards structural components and towards storage compounds that assure a steady carbon supply over the complete diurnal cycle. We used 14 CO2 labelling to track assimilated carbon in both source and sink tissues. Source tissues exhibit large variations in carbon allocation throughout the light period. The most prominent change was detected in partitioning towards starch, being low in the morning and more than double later in the day. Export into sink tissues showed reciprocal changes. Fewer and smaller changes in carbon allocation occurred in sink tissues where, in most respects, carbon was partitioned similarly, whether the sink leaf assimilated it through photosynthesis or imported it from source leaves. Mutants deficient in the production or remobilisation of leaf starch exhibited major alterations in carbon allocation. Low-starch mutants that suffer from carbon-starvation at night allocated much more carbon into neutral sugars and had higher rates of export than the wild type, partly due to the reduced allocation into starch but also due to reduced allocation into structural components. Moreover, mutants deficient in the plants circadian system showed considerable changes in their carbon partitioning pattern suggesting control by the circadian clock.
Kölling K, Thalmann M, Müller A, Jenny C and Zeeman SC.