SECTORIAL ROOT-GROWTH IN CUTTINGS OF COLEUS-REHNELTIANUS IN RESPONSE TO LOCALIZED AERIAL DEFOLIATION

Asymmetries in root growth in response to localized aerial defoliation were examined in Coleus rehneltianus (Lamiaceae). We confirmed that a ssimilate transport was sectorial by examining the distribution of C-1 4-labeled carbohydrates following a 24-h chase period. Integrated phys iological units (IPUs), or sectors, extended from the leaves into the roots, and this was reflected in the differential growth of roots foll owing artificial defoliation of part of the leaf canopy. When defoliat ion was localized within leaves or leaf halves within sectors, roots g rew asymmetrically, with decreased root growth in defoliated sectors. Three root populations were identified by their location and growth re sponses: stem side, stem corner, and bottom side roots, and asymmetric growth was observed in all three populations. Only the growth of stem corner roots, which made up 35-90% of dry mass of the total root popu lation, was influenced by the pattern of aerial defoliation. In contra st, asymmetries in the growth of the ether two root populations appear ed to reflect the distribution of leaf biomass prior to defoliation.