CARBON IMPORT INTO BARLEY ROOTS - STIMULATION BY GALACTOSE

Galactose was applied to one-half of a split root system of barley. It stimulated import of photoassimilate labelled with C-11 from leaf 2 into that root half at concentrations from 0.2-50 mol m(-3). The lag before an increase in import was detected decreased from >60 to <30 min as concentration of galactose was increased across this range. In the presence of 10 mol m(-3) glucose, 2 mol m(-3) galactose did not increase import of C-11. Whilst 2 and 50 mol m(-3) galactose had no effect on respiratory oxygen uptake of roots, they caused a rise in the rate of evolution of (CO2)-C-11, in <5 min. Galactose at 2 mol m(-3) reduced the rate of elongation of the seminal root axis, but only more than 4 h after applying it; elongation growth had ceased by 6 h. These results are discussed in the context of control of translocatory import of carbon into elongating barley roots.