PATTERNS OF SOLUTE IN INDIVIDUAL MESOPHYLL, BUNDLE-SHEATH AND EPIDERMAL-CELLS OF BARLEY LEAVES INDUCED TO ACCUMULATE CARBOHYDRATE

After cooling the roots and shoot apex of barley, there is a reduction in sucrose export from, and an increased total accumulation of carboh ydrate and induction of fructan synthesis in, source leaves. We invest igated carbohydrate accumulation in individual leaf cells. Using the m icrosampling technique and microfluorometric enzymatic assay, the amou nts of various carbohydrates were measured in mesophyll, bundle sheath and epidermal cells. Epidermal cells take no part in carbohydrate par titioning and have very low concentrations of sugars even when leaf ex port is reduced. Even without cooling, however, there are remarkable c hanges in sucrose concentration (up to 200 mM) in mesophyll and bundle sheath cells during the photoperiod. The activity of acid invertase i n samples from individual cells was very low, c. 3 mu mol sucrose (g f . wt)(-1) h(-1). Interrelationships between these cell types and the c ontrol of fructan metabolism are discussed.