Concomitant analysis of cambial abscisic acid and cambial growth activity in poplar

Endogenous levels of cambial region abscisic acid (ABA) were quantified by immunoassay and assessed together with cambial growth activity in poplar (Populus nigra L. × P. maximowiczii Henry, clone Kamabuchi) over the course of a growing season. The level of cambial region ABA increased from spring to late-summer but decreased sharply in autumn. Cambial growth activity, measured as the radial number of undifferentiated cambial cells and enlarging xylem cells, also increased from spring to summer and decreased sharply in autumn, indicating the onset of cambial dormancy. Exogenous ABA, applied laterally to poplar stems at two times within the growing season, enhanced cambial growth activity, as the radial number of undifferentiated cambial cells increased in ABA-treated trees subsequent to the two application times. Xylem cell development was also affected by exogenous ABA as fibre length increased significantly in ABA-treated trees at both application times. The positive correlation of cambial region ABA and cambial growth activity as well as the positive effects of exogenous ABA application thereon sheds new light on the role of this hormonal growth regulator.