HORMONAL PHYSIOLOGY OF WOOD GROWTH IN WILLOW (SALIX-VIMINALIS L) - EFFECTS OF SPERMINE AND ABSCISIC-ACID

Willow cuttings from two-year-old twigs were grown in nutrient solutio n alone, nutrient solution with 0.1 mM abscisic acid or with the sperm ine. Roots and leaves emerged within three weeks and the cambium was a ctivated in the shoot. In most cases earlywood was generated, even whe n the seedlings were made in late summer. In contrast to plantlets gro wn in regular nutrient solution, those treated with hormones either in hibited (ABA) or advanced (spermine) the formation of roots, leaves an d wood. In addition, SEM observations of wood were combined with autor adiographic studies and metabolite analysis. C-14-labeled photoassimil ates from the leaves were unloaded from the phloem of the shoots and t ransported via the rays into the cambial zone and the xylem. In spermi ne treated plants labeled assimilates were highly concentrated in all cells of the newly built xylem. However, cells from plants treated wit h abscisic acid appeared only weakly labeled. Quantitative analysis of the assimilates after two-dimensional thin-layer chromatography shelv ed that wood from spermine-treated plants accumulated 19% more assimil ates than the control, while xylem from ABA-treated plants imported 81 % less labeled compounds from the phloem. Thus, the results strongly s upport the view that hormones play a key role in wood formation.