Ecotype-dependent control of growth,dormancy and freezing tolerance under seasonal changes in <Emphasis Type="Italic">Betula pendula</Emphasis> Roth

Woody plants in the temperate and boreal zone undergo annual cycle of growth and dormancy under seasonal changes. Growth cessation and dormancy induction in autumn are prerequisites for the development of substantial cold hardiness in winter. During evolution, woody plants have developed different ecotypes that are closely adapted to the local climatic conditions. In this study, we employed distinct photoperiodic ecotypes of silver birch (Betula pendula Roth) to elucidate differences in these adaptive responses under seasonal changes. In all ecotypes, short day photoperiod (SD) initiated growth cessation and dormancy development, and induced cold acclimation. Subsequent low temperature (LT) exposure significantly enhanced freezing tolerance but removed bud dormancy. Our results suggested that dormancy and freezing tolerance might partially overlap under SD, but these two processes were regulated by different mechanisms and pathways under LT. Endogenous abscisic acid (ABA) levels were also altered under seasonal changes; the ABA level was low during the growing season, then increased in autumn, and decreased in winter. Compared with the southern ecotype, the northern ecotype was more responsive to seasonal changes, resulting in earlier growth cessation, cold acclimation and dormancy development in autumn, higher freezing tolerance and faster dormancy release in winter, and earlier bud flush and growth initiation in spring. In addition, although there was no significant ecotypic difference in ABA level during growing season, the rates and degrees of ABA alterations were different between the ecotypes in autumn and winter, and could be related to ecotypic differences in dormancy and freezing tolerance.     

Nitrogen fixation rates of Stereocaulon vulcani on young Hawaiian lava flows

Previous research has suggested thatnitrogen-fixing lichens can play an importantrole in the nitrogen cycle of early primarysuccessional systems and other extremeenvironments. In this study, we estimaterates of nitrogen fixation by anitrogen-fixing lichen, Stereocaulonvulcani, at 1500 m on the northeast slope ofMauna Loa volcano. Using microclimatemeasurements and a climate-driven model ofnitrogen fixation, we estimate that S.vulcani fixes between 0.2 and 0.45 kg N ha^–1yr^–1. We calculate that S. vulcanicould have derived 40% of its nitrogencontent from biological fixation.     

Lack of influence of photoperiod on the metabolism of gibberellin A20 in Salix pentandra

The influence of photoperiod on the metabolism of GA₂₀ in Salix pentandra was studied by feeding [³H]-GA₂₀ to seedlings which had been grown previously under long day (LD) or short day (SD) conditions. After 48 h in LD or SD, metabolites were separated on sequential, silica gel partition columns and reversed-phase C₁₈ HPLC. The principal metabolite co-chromatographed with [³H]-GA₁ and this conversion was confirmed by feeding [²H]-GA₂₀, which was converted to [²H]-GA₁ as identified by gas chromatography-selected ion monitoring. Chromatographic evidence also indicated the minor conversion of [³H]-GA₂₀ to [³H]-GA₈ (via [³H]-GA₁) and trace conversion to [³H]-GA₂₉ (GAs A_1.8,20.29 are native in Salix). Ethyl acetate-insoluble [³H] metabolites were formed and could be cleaved by cellulase to release putative [³H]-GA₂₀ and [³H]-GA₁ suggesting the conversion to glucosyl conjugates of these GAs. Metabolism of [³H]-GA₂₀ was slightly more rapid in plants previously grown under LD than SD, an effect which reflected the generally increased shoot growth under LD. However, altering the photoperiod after [³H]-GA₂₀ addition had only a slight effect on the metabolism of [³H]-GA₂₀ in Salix seedlings. This indicates that the conversion of GA₂₀ to GA₁ is not a controlling step in the photoperiodic regulation of growth cessation in Salix.     

Transformable mutants of a biopesticide strainStreptomyces griseoviridis K61

Summary The aim of this work was to isolate transformable mutants ofStreptomyces griseoviridis K61 without affecting the secondary metabolism of this strain.S. griseoviridis K61 produces an antifungal aromatic heptaene polyene antibiotic, and is used as a biological control agent. In protoplast transformation experiments using plasmid pIJ702 DNA, the few spontaneous transformants were phenotypically bald and their secondary metabolism was pleiotropically affected. By mutagenizing K61 withN-methyl-N-nitro-N-nitrosoguanidine (MNNG) a highly transformable variant K61-42 was obtained. Protoplasts ofS. griseoviridis K61-42 could be transformed by several model plasmids producing 10⁴–10⁵ transformants/g plasmid DNA. The polyene synthesis of K61-42 was normal, making this strain a useful tool in genetic studies on the mechanism of biopesticide action.     

The eutrophication history of Lake Särkinen,Finland and the effects of lake aeration

Lake Särkinen is a small lake in the parish of Sotkamo, Finland. The lake has been strongly enriched since the middle of the 1960's. The nutrient load was greatly reduced in 1969 and aeration was started in 1980.According to ²¹⁰Pb dating sediment accumulation rates are lowest (ca 9 mg cm^–2 yr^–1) between about 1920 and 1960. Thereafter they rise to the present level (22 mg cm^–2 yr^–1).The diatom flora indicates rising eutrophy from the beginning of the 20th century and again in the 1950–60's period. The surface sample, which represents the 1980's, shows a change in diatom flora indicating lake recovery. Changes in nutrient concentrations and in the solubility of phosphorus in the sediments indicate signs of oxygen depletion.     

Effect of hydrocortisone on catecholamines and the enzymes synthesizing them in the developing sympathetic ganglion

Summary Newborn rats were daily injected with 0.2 mg hydrocortisone acetate for seven days. They were killed 1, 7 or 21 days after the last injection, together with untreated controls. Hydrocortisone caused a great increase in the number of the small, intensely fluorescent (SIF) cells and the appearance of similar small cells with intense immunohistochemical reactions for tyrosine hydroxylase (TH), dopamine--hydroxylase (DBH) and phenylethanolamine (noradrenaline)N-methyltransferase (PNMT) in the superior cervical ganglion. At the same time, the adrenaline content and the PNMT activity of the ganglion greatly increased, while no significant changes were observed in the dopamine or noradrenaline content or TH or DBH activity. All these changes essentially disappeared after a recovery period of seven or 21 days.It is concluded that hydrocortisone causes a temporary increase in the number of SIF cells by causing a synthesis of TH, DBH and PNMT in previously existing small, non-fluorescent cells, which start to synthesize and store adrenaline, thus becoming intensely fluorescent SIF cells. These SIF cells are different from the normal SIF cells of the same ganglion, most of which appear at a later stage of postnatal development when response to hydrocortisone is lost, which contain TH but neither DBH nor PNMT, and which permanently remain in the ganglion.     

Effects of different gibberellins on elongation growth under short day conditions in seedlings of Salix pentandra

Fifteen different gibberellins (GA's) were tested for their ability to induce elongation growth under short day conditions in seedlings of Salix pentandra L. GA's were applied either to the apex or they were injected into a mature leaf. GA₃ was highly active and also GA₄₊₇ and GA₄ showed high activity. GA₁, GA₂, GA₅, GA₉, GA₁₃, GA₂₀, GA₃₆ and GA₄₇ showed moderate activity. GA₁₆, GA₁₇, GA₂₇ and GA₄₁ exhibited low or no activity in doses up to 10 μg per plant. In general, a better growth response was obtained with an application to the apex than with an injection into the leaf.     

Induction of aryl hydrocarbon hydroxylase in human fetal liver cell and fibroblast cultures by polycyclic hydrocarbons

Cells originating from the human fetal liver and grown as a primary monolayer culture for 4 to 11 days contain an enzyme system that metabolizes benzo(α) pyrene. The basal level of the enzyme varied about three-fold. The activity was increased from 1.4- to 5.1-fold by the exposure of cells for 24 hours to benz(α) anthracene, the magnitude of increase depending on the amount of inducer, on the individual cell batch studied and on the stage of cell growth. Also 3-methylcholanthrene, but not benzo(α)pyrene, induced the enzyme activity in fetal liver cell cultures at concentrations used. Fibroblast cultures derived from the human fetal lung or skin exhibited less benzo(α)pyrene metabolism and the inducibility of the enzyme activity was less marked than in hepatic cell cultures.     

Histochemical correlates of cold-induced trans-synaptic induction in the rat superior cervical ganglion

Synopsis The effect of prolonged pre-ganglionic activity induced by exposure to cold (5°C) was studied in intact and decentralized superior cervical ganglia of rats. Intact and decentralized ganglia of rats kept at room temperature served as controls. catecholamines were demonstrated histochemically using the formaldehyde-induced fluorescence method. The intensity of the fluorescence of the nerve cell bodies was estimated both visually and photometrically.Decentralization in itself had no effect on the intensity of the cell bodies for up to 16 days. Exposure to cold had no effect on the decentralized ganglia but caused a marked increase in the fluorescence intensity of some nerve cells of the intact ganglia, indicating that the increased fluorescence was mediated by the pre-ganglionic nerves. The increase lasted for the whole 16-day-length of exposure to cold.It is suggested that the observed change in the fluorescence intensity reflects an increase of the enzymes tyrosine hydroxylase and dopamine--hydroxylase, and thus represents a histochemical correlate of trans-synaptic induction.Sigrid Jusélius Foundation Research Fellow in the Department of Anatomy, University of Helsinki, April–July 1973.     

Experimental control of flowering and vivipary in timothy (Phleum pratense)

Environmental and hormonal control of flowering and vivipary in four Norwegian timothy ( Phleum pratense L.) cultivars has been studied in phytotron and by aseptic culture of inflorescence explants. The critical photoperiod for flowering increased with increasing temperature (12–18°C) and it was 13 to 15 h for the southern and 14 to 16.5 h for the northern cultivars. Diurnal temperature fluctuation significantly stimulated flower formation compared to the corresponding constant temperature treatment. Plants grown in 16-h photoperiod contained normal sexual flowers, but a high percentage of spikes developed in 12- or 14-h photoperiod contained viviparous plantlets. One- to four-weeks in continuous light before treatment with 12-h photoperiod increased the number of spikes per plant, but did not enhance the frequency of vivipary. Experiments with aseptic cultures showed that generative versus vegetative development of timothy inflorescence was affected by plant hormones. Kinetin stimulated the vegetative development and induced proliferation both in inflorescence initials and in spikelets isolated at heading time.