RE-SORPTION OF ORGANIC-COMPOUNDS BY ROOTS OF ZEA-MAYS L AND ITS CONSEQUENCES IN THE RHIZOSPHERE .3. CHARACTERISTICS OF SUGAR INFLUX AND EFFLUX

The influx and efflux of sugar-C and the cycling of C within intact ma ize roots (Zea mays L.) was studied in sterile solution culture. Using metabolic inhibitors it was shown that roots could take up sugars aga inst the concentration gradient probably via H+-ATPase dependent plasm alemma proton cotransporters. In contrast to this, no evidence was fou nd for an ATPase mediated efflux of sugars from the root. All parts of the root were capable of taking up exogenous sugars. Examination of s ugar exudation sites along the root slowed efflux at all locations, wi th the amount of efflux linearly correlated with internal cellular con centration. The results clearly indicated that the influx-efflux mecha nisms are linked both spatially, temporally and with respect to the su gars capable of transportation. The turnover of C within the root was found to be extremely rapid with turnover of the soluble sugar pool be ing 0.8 to 15 times daily depending on root spatial location. The resu lts strongly suggest that the recapture of sugars from outside the roo t plays an important role in regulating the amount of C lost to the so il which in turn will reduce both pathogen attraction and the size of the rhizosphere microbial population and will also increase the plant' s C efficiency.