CONTINUOUS MONITORING OF FLUXES OF PHOTOASSIMILATE IN LEAVES AND WHOLE PLANTS

A technique is described for continuous, simultaneous and in vivo monitoring of the photosynthetic uptake of carbon, the transport of carbon from the leaf, and its transport throughout the entire plant. Continuous but varying amounts of carbon-11 dioxide are supplied to a leaf while observing the amount of labelled photoassimilate that appears in different parts of the plant. Appropriate analysis of these tracer profiles gives physiologically meaningful parameters such as the fraction of recent assimilate which is exported from the leaf. Variation in these parameters can be followed over an indefinite time, to follow the effects of natural rhythms or treatments. The method does not require any assumptions about mechanism, nor the assumption that transport processes within the leaf are constant, unlike compartmental analysis of efflux data sometimes used to infer fluxes in leaves. The method is illustrated by an experiment with a young barley plant where the export fraction from a leaf is found to reduce through the day, and to respond immediately after the leaf is shaded.