Publications
NIBIOs employees contribute to several hundred scientific articles and research reports every year. You can browse or search in our collection which contains references and links to these publications as well as other research and dissemination activities. The collection is continously updated with new and historical material.
1993
Authors
Harald Kvaalen Arild ErnstsenAbstract
It is known that reducing the partial pressure of O2 influences the induction of somatic embryogenesis. We tested the hypothesis that O2 causes changes in the endogenous levels of exogenously supplied benzyladenine (BA) or 2,4-dichlorophenoxyacetic acid (2,4-D).Embryogenic tissue of Picea abies was incubated under reduced (2.5, 5 kPa) and ambient (21 kPa) levels of O2 for 1, 3, 7 and 11 days and the endogenous concentrations of BA and 2,4-D were measured. For all treatments the concentration of BA in the tissue increased until the third day. At day 3, the ratio of BA in the tissue relative to the initial concentration in the medium, was 3.9, 2.8 and 1.9 for tissue incubated under 2.5, 5 and 21 kPa O2, respectively. The BA concentration then declined gradually. Uptake of 2,4-D was inhibited at low O2 levels.However, 2,4-D gradually accumulated in tissue grown under hypoxia, so that high levels were reached by day 11. These shifts in the BA and 2,4-D levels also caused a transient increase in the BA to 2,4-D ratio in tissue incubated under hypoxia. Although relevant for the previously reported effects of oxygen on induction of embryogenic tissue, it is unlikely that oxygen-induced alterations in BA and 2,4-D levels alone suffice to explain these findings.
Authors
Alhaji S. Jeng B. R SinghAbstract
No abstract has been registered
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Abstract
The pathogenicity of the blue-stain fungi Leptographium wingfieldii Morelet and Ophiostoma minus (Hedgc.) H. et P. Syd. associated with the pine shoot beetle Tomicus piniperda (L.), was determined on pruned and unpruned Seots pine (Pinus sylvestris L.) trees. Both fungi killed unpruned trees when inoculated in a 60 cm wide band at a density of 800 inoculations/m2, while severely pruned trees were killed by an inoculation density of 400 inoculations/m2. Trees inoculated with L. wingfieldii died sooner after inoculation than trees inoculated with O. minus.
Authors
Oddvar SkreAbstract
The measurements were carried out on excised leaf discs and intactplants by infrared gas analyser technique. The sample plants had been grown for six weeks in varying temperature, light and daylengths. The photorespiration was estimated from measurements at low oxygen level. A strong temperature acclimation effect was found on CO2 exchange rates. Long term low-temperature treatment caused a reduction in photosynthesis and its temperature optimum in all birch populations. Strong acclimation effects of light were also found. Short term (48 hours) low-temperature treatment reduced photosynthesis rates at low light levels. Mountain birch from northern or arctic populations showed relatively high net photosynthetic rates compared with southern populations.
Abstract
No abstract has been registered
Authors
R. Minocha Harald Kvaalen S.C. Minocha S. LongAbstract
Embryogenic cultures of red spruce (Picea rubens Sarg.) and Norway spruce (Picea abies (L.) Karst.) were initiated from dissected mature zygotic embryos. The tissues were grown on either proliferation medium or maturation medium. On proliferation medium, the embryogenic tissue continued to produce early stage somatic embryos (organized meristems attached to elongated, suspensor-like cells), whereas on maturation medium fully mature embryos developed from the embryonic tissue. Analysis of polyamines in tissues grown on these two media showed that: both putrescine and spermidine concentrations were always higher in cultures grown on proliferation medium than in cultures grown on maturation mediumin both species, spermidine concentrations declined with time in the tissues grown on maturation medium spermine was present in only minute quantities and showed only a small change with time. The presence of difluoromethylomithine in the culture medium had little effect on polyamine concentration, whereas the presence of difluoromethylarginine caused a decrease in putrescine concentrations in both red spruce and Norway spruce tissues grown on proliferation medium or maturation medium.
Abstract
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Abstract
Root dieback of Picea abies (L) Karst., Norway spruce, seedlings is a serious problem in Scandinavian forest nurseries. We have chosen spruce seedlings infected with a pathogenic Pythium sp. isolate as an experimental system to study the interaction between the roots of a gymnosperm and a pathogen at the protein level. In this infection system, necroses on the hypocotyl and browning of the upper part of the roots appear within 2 days. Within 10 days the seedlings are completely wilted. Low pH soluble PR-proteins from infected and uninfected roots have been resolved on isoelectrofocusing (IEF) gels. Chitinases, chitosanases and β-1,3-glucanases have been detected enzymatically after IEF. Our results show that more than 30 different pathogenesis-related (PR) proteins accumulated in roots after pathogen infection. PR proteins of low and high isoelectric points appeared within 2 days after infection. In uninfected plants, only one acidic protein was detected. Eight different isoforms of chitinases accumulated after pathogen infection. Two acidic chitinases were constitutively expressed, and one of these strongly accumulated following pathogen infection. Three chitosanase activities were observed in infected plants, while no chitosanase activity was detected in uninfected plants. Also, no β-1,3-glucanase activity was observed in uninfected plants. One acidic β-1,3-glucanase was detected in infected roots after the second day of infection. A second acidic β-1,3-glucanase of relatively higher pI was detected on the fourth day. To our knowledge, this is the first report describing the response of gymnosperm roots to pathogen infection at the protein level. For the first time, we show that PR proteins accumulating after pathogen infection also include chitosanases. It can be concluded from our results that although gymnosperms are evolutionarily very distant from angiosperms, in terms of the production of PR proteins the response of gymnosperm roots resembles that observed in angiosperms.