Apparent auxin production and transport during winter in the nongrowing pine tree

Endogenous indol-3yl acetic acid (IAA) was characterized by combined gas chromatography – mass spectroscopy (GC–MS) in inactive cambia of Pinus contorta Dougl. and Larix decidua Mill, during winter, and IAA levels were estimated by GC–MS in buds, needles, and the tissues comprising the inactive cambial region of P. contorta during late autumn and winter. Supplementary IAA estimates were obtained for cambia of Acer pseudoplatanus L., L. decidua, Populus × canadensis 'Robusta,' and Quercus robur L. IAA levels in cambial tissue of lodgepole pine were higher than those in similar-aged tissue of hardwoods throughout the winter.Both winter disbudding and defoliating treatments reduced levels of endogenous IAA in the cambial region of lodgepole pine. Moreover, exogenous [14C]IAA and [14C]sucrose were transported downward in the stem during winter. Microscopy suggested functional sieve cells to be present during winter, and the moisture content of the cambial region of lodgepole pine was more than twice that of overwintering hardwoods.Thus, the vascular cambium of P. contorta probably is not dependent upon a supply of IAA from extending shoots and growing needles for its reactivation in spring. The findings also suggest that IAA production and export from metabolically active buds and mature needles may occur during winter.