MATURATION-RELATED LOSS IN ROOTING COMPETENCE BY LOBLOLLY-PINE STEM CUTTINGS - THE ROLE OF AUXIN TRANSPORT, METABOLISM AND TISSUE SENSITIVITY

A comparison of rooting ability of stem cuttings made from hypocotyls and epicotyls from 50-day-old seedlings of loblolly pine (Pinus taeda L.) reveals a dramatic decline by epicotyl cuttings, which do not root at all in 20-30 days in the presence or absence of auxin. In contrast , almost all the hypocotyls root during this time, but only in the pre sence of exogenously applied auxin. The failure of epicotyls to root d oes not appear to be due to differences in [C-14] labeled auxin uptake , transport, metabolism, or tissue distribution in the two types of cu ttings. At the cellular level, initial responses to auxin, such as dif ferentiation of the cambium into parenchyma, occur in both types of cu ttings, but localized rapid cell division and root meristem organizati on are not observed in epicotyls. Autoradiography revealed that radioa ctivity from alpha-naphthalene acetic acid is bound in the cortex but not concentrated at sites of root meristem organization prior to the o rganization of the meristem in hypocotyls. During the development of t he epicotyl, cellular competence to form roots appears to be lost. Alt hough this loss in competence is not associated with a concurrent loss in ability to transport auxin polarly, the latter process appears to play a key role in rooting other than to move auxin to the site of roo t formation. The phytotropin N-(1-naphthyl)phthalamic acid inhibits ro oting if applied during the first 3 days after the cutting is made, bu t does not affect auxin concentration or metabolism at the rooting sit e.