Roland Grönroos PhD Thesis

Direct rooting and rooting via a wound tissue in Pinus sylvestris L. and Pinus contorta Dougl. ex Loud. hypocotyl cuttings in vitro were studied. Direct rooting usually occurred within three weeks after cutting. Three to four weeks after cutting, roots developed either directly on the hypocotyl or via a wound tissue. Later than one month after cutting, rooting took place predominantly via a wound tissue. Anatomical studies showed that certain tissues in the hypocotyl could either form wound tissue or roots. Cuttings not treated with auxin developed a wound tissue from which roots eventually emerged. Wound tissues were usually fairly organized structures consisting of a central tracheid nest surrounded by meristematic tissue. Auxin treatment was necessary for direct rooting in vitro. When the cuttings were treated with auxin (IAA or IBA), roots usually developed outside resin ducts, in vertical rows along the length of the hypocotyl. Optimal auxin treatments for direct rooting of Pinus sylvestris and Pinus contorta were defined in terms of the time course for development of roots and the yield of rooted cuttings within one month. The optimal auxin treatments for Pinus contorta gave rooting percentages of more than 80% within 19 days and half of the cuttings which possessed roots after one month had acquired them within 14 days. For Pinus sylvestris , the optimal auxin treatments gave a lower yield (45%) of directly rooted cuttings. Uptake studies with tritium-labeled IAA showed that the cuttings had a passive mode of IAA uptake. The optimal IAA treatment for direct rooting of Pinus contorta (6 h with 5.71 mM) resulted in a mean IAA concentration (5.55 μmol/g fresh weight) in the basal 3 mm of the hypocotyl that was similar to that in the treatment solution. Eighteen hours after transfer to new culture medium, the IAA concentration was 1.4 and 2.0 μmol/g fresh weight respectively in the upper and basal parts of the hypocotyl, which was where root initiation took place. Differences between individual cuttings in auxin uptake could not explain the poor direct rooting of Pinus sylvestris hypocotyl cuttings cultured in vitro. In vitro culture inhibited root elongation growth. However, after transfer of rooted cuttings from in vitro to hydroponic culture, root elongation growth increased markedly. Additional keywords Adventitious, activated charcoal, anatomy, AOPP, auxin, bud, conifer, IAA, IBA, Lodgepole pine, mitosis, PAL, peroxidase, phenylalanine ammonia-lyase, root, Scots pine, seedling, tracheid, wound tissue. Roland Grönroos, Department of Physiological Botany, Uppsala University, Box 540, S-751 21 Uppsala, Sweden. ISSN 0282-7468 ISBN 91-554-2056-7 Uppsala 1987 © Roland Grönroos 1987