Initiation of roots on hypocotyl cuttings of Pinussylvestris, with emphasis on direct rooting, root elongation, and auxin uptake

Abstract

Direct rooting of hypocotyl cuttings of Pinussylvestris L. is described and compared with rooting via wound tissue. The optimal 3-indolylbutyric acid treatment for direct rooting of Pinussylvestris hypocotyl cuttings under in vitro conditions was 1.23 mM for 24 h. This treatment resulted in 45% rooting within 3 weeks after cutting. During this period, only direct rooting was observed. Three to 4 weeks after cutting, roots developed either directly on the hypocotyl or via wound tissue. After the first month, rooting took place predominantly via wound tissue. The optimal 3-indolylbutyric acid treatment found for in vitro culture could successfully be used for hydroponic culture (under nonsterile conditions). In vitro culture inhibited root elongation. However, after transfer of rooted cuttings from in vitro to hydroponic culture, root elongation increased markedly. Uptake studies with 3-[5(n)-3H]indolylacetic acid mixed with the nutrient solution showed that auxin uptake by the cutting probably occurred mainly through uptake of the nutrient solution. After 24 h treatment with 1.43 mM 3-indolylacetic acid, the concentration taken up by the cuttings was 0.91 nmol/mg fresh weight. Differences between individual cuttings in auxin uptake could not explain the poor direct rooting of Pinussylvestris hypocotyl cuttings cultured in vitro.