After cooling the roots and shoot apex of barley, there is a reduction
in sucrose export from, and an increased total
accumulation of carbohydrate and induction of fructan synthesis in, source
leaves. We investigated carbohydrate
accumulation in individual leaf cells. Using the microsampling technique and
microfluorometric enzymatic assay,
the amounts of various carbohydrates were measured in mesophyll, bundle
sheath and epidermal cells. Epidermal
cells take no part in carbohydrate partitioning and have very low
concentrations of sugars even when leaf export
is reduced. Even without cooling, however, there are remarkable changes in
sucrose concentration (up to 200 mM)
in mesophyll and bundle sheath cells during the photoperiod. The activity of
acid invertase in samples from
individual cells was very low, c. 3 μmol
sucrose (g f. wt)−1 h−1.
Interrelationships between these cell types and the
control of fructan metabolism are discussed.