Sun and shade leaves in Betula pubescens and Betula pendula

Summary

Measurements of the net photosynthesis and dark respiration rates of excised twigs from Betula pubescens Ehrh. subsp. odorata (Bechst.) Warburg and B. pendula Roth, at different light intensities were made using infra-red gas analysis. B. pubescens appears to possess leaves which on the basis of physiological responses can be described as sun and shade leaves. In the more open canopy of B. pendula differences between leaf types are less pronounced. The presence of sun and shade leaves is suggested as a means whereby the net assimilation rate of the shrubby growth form of B. pubescens can be increased. This type of mechanism becomes increasingly important at high altitudes and latitudes.     

Denitrification and Assimilatory Nitrate Reduction in Aquaspirillum magnetotacticum

Aquaspirillum magnetotacticum MS-1 grew microaerobically but not anaerobically with NO₃⁻ or NH₄⁺ as the sole nitrogen source. Nevertheless, cell yields varied directly with NO₃⁻ concentration under microaerobic conditions. Products of NO₃⁻ reduction included NH₄⁺, N₂O, NO, and N₂. NO₂⁻ and NH₂OH, each toxic to cells at 0.2 mM, were not detected as products of cells growing on NO₃⁻. NO₃⁻ reduction to NH₄⁺ was completely repressed by the addition of 2 mM NH₄⁺ to the growth medium, whereas NO₃⁻ reduction to N₂O or to N₂ was not. C₂H₂ completely inhibited N₂O reduction to N₂ by growing cells. These results indicate that A. magnetotacticum is a microaerophilic denitrifier that is versatile in its nitrogen metabolism, concomitantly reducing NO₃⁻ by assimilatory and dissimilatory means. This bacterium appears to be the first described denitrifier with an absolute requirement for O₂. The process of NO₃⁻ reduction appears well adapted for avoiding accumulation of several nitrogenous intermediates that are toxic to cells.     

Procyanidin xylosides from the bark of Betula pendula

A procyanidin dimer xyloside, catechin-(4α → 8)-7-O-β-xylopyranosyl-catechin, was isolated from the inner bark of Betula pendula and its structure was determined using 1D and 2D NMR, CD and high-resolution ESIMS. Interestingly, the 7-O-β-xylopyranose unit was found to be present in the lower terminal unit of the dimer. In addition to this procyanidin dimer xyloside, an entire series of oligomeric and polymeric procyanidin xylosides was detected. Their structures were investigated by hydrophilic interaction HPLC–HRESIMS. Procyanidin glycosides are still rarely found in nature.     

Pollen–pollen interactions in Betula pendula in vitro

Direct pollen interactions, as well as interactions mediated by a recipient, can have a remarkable influence on pollen fertilization ability. Under conditions of pollen competition it could be advantageous if pollen grains interfered with the germination of other pollen. The aim of this study was to find out if there are direct negative or positive pollen–pollen interactions between pollen grains from genetically slightly different donors. The in vitro germinability of the pollen from several Betula pendula Roth clones was investigated. The pollen interactions between the clones were examined pairwise by using equal pollen mixtures. In three of the eight cases the germination percentage of the pollen mixture was significantly higher than the average germination percentage of the separate clones that formed the mixture, which indicates some type of interaction between the pollen populations. We found only positive interactions between the pollen of clones. This study also documented density-dependent germination of pollen grains in vitro (=pollen population effect). Adding an aqueous pollen extract to the incubation medium increased the germination percentages of poorly germinating pollen and small pollen populations. Germination-stimulating effects were found to exist both with fresh and dead pollen. Such direct pollen–pollen interactions could be explained by specific water-soluble substances diffusing from pollen grains.     

Cryopreservation of conditionally dormant orthodox seeds of Betula pendula

To evaluate the feasibility of long-term cryopreservation of Polish provenances of silver birch (Betula pendula), the sensitivity of conditionally dormant seeds to extreme desiccation and/or the ultra-low temperature of liquid nitrogen (LN; ?196°C) was evaluated. The critical water content (WC) of desiccated seeds and the high-moisture freezing limit of seeds desiccated or moistened to various WCs and frozen for 24 h or for 2 years in LN was also determined. Germination tests revealed no critical WC for seeds [to 0.02 g H₂O g^?1 dry mass (g g^?1)]. Seeds tolerated freezing in LN within specific safe range of WC 0.02–0.23 g g^?1 (nuts). Seeds desiccated to the safe WC and stored in LN for 2 years had similar or higher germination as seeds stored at ?3°C for 2 years, depending on provenance. Therefore, long-term cryopreservation of B. pendula seeds in gene banks is feasible.     

Energy-dependence of the Assimilatory Nitrate Uptake in Azorhizobium caulinodans Strain IRBG 46

Nitrate assimilation by suspensions of Azorhizobium caulinodans strain IRBG 46, as determined by disappearance of nitrate ions from the external medium, displayed the requirement of readily utilizable carbon source. Nitrate uptake was blocked by the uncouplers of oxidative phosphorylation such as 2,4-dinitrophenol, carbonyl cyanide m-chlorophenyl hydrazone and by an inhibitor of ATPase, N, N — dicyclohexyl carbodiimide. The inhibition of nitrate assimilation in the absence of appropriate carbon source was not overcome by the non-physiological terminal electron donor ascorbate plus N-methyl phenazinium methyl sulphate, a substrate combination that allows electron transfer to O₂ without the synthesis of ATP. These data suggest that transport of nitrate into the cell is directly dependent on ATP.     

Potassium nutrition and free polyamines of Betula pendula Roth and Betula pubescens Ehrh.

Potassium and free polyamine concentrations in the leaves of silver birch (Betula pendula Roth) and downy birch (Betula pubescens Ehrh) were followed during three successive growing seasons 1996, 1997 and 1998 in order to define K deficiency levels.The highest foliar K concentrations were found in June. In August, the K concentrations were lower and remained quite stable in Betula pendula but varied in Betula pubescens. In addition to a common diamine, putrescine, and the polyamines, spermidine and spermine, also a less common diamine and polyamine, 1,3-diaminopropane and norspermidine were found in the birch leaves. The accumulation of both diamines, putrescine and 1,3-diaminopropane, was used to define the critical levels of K nutrition in birch leaves. Foliar K concentrations below 7–8 mg g ^–1 DW were found to correlate with the accumulation of diamines at most sampling dates.     

Photosynthetic efficiency during ontogenesis of leaves of Betula pendula

Abstract. Net photosynthesis, photosynthetic electron transport, and leaf area density of photosynthetic units have been studied in developing, mature, and old leaves of seedlings of Betula pendula . The photosynthetic quantum yield under light-limiting conditions and the leaf area related rale of light-saturated net photosynthesis were lower in developing than in mature and old leaves. Developing leaves also had more oxygen inhibition of photosynthesis, a lower pool size of plastoquinone in the electron transport chain, a lower chlorophyll content and a lower leaf area density of photosynthetic units than mature and old leaves. The photosynthetic properties of The oldest leaves resulted partly from acclimation to shade and partly from a different ontogeny to that of younger leaves.     

Herbivore-induced resistance in Betula pendula: the role of plant vascular architecture

We studied the role of plant vascular architecture in the determination of the spatial extent of herbivore induced responses within Betula pendula Roth saplings. The induced responses were measured in bioassays in terms of the relative growth rate of larvae of a geometrid moth, Epirrita autumnata. We hypothesised that the level of induced resistance of a certain leaf would be determined by the degree of vascular connectivity between the leaf in question and a damaged leaf, as suggested by recent theoretical and empirical studies. A comparison of the control plants with the damaged plants indicated that damaging one leaf of a sapling was sufficient to induce an increase in the resistance level. There were also differences among the leaves within a plant in the resistance level, but these differences could not be explained by the degree of vascular connectivity with the damaged leaf. These results suggest that the vascular connections have low power as explanations of the spread and spatial extent of the induced resistance in Betula pendula saplings Instead, the resistance level of all leaves within a sapling increased following the damage. We suggest that the pattern of increased resistance observed in this experiment may be beneficial for the young saplings studied. For young saplings at their early stages of development, it may be beneficial to be able to distribute the induction signal to all leaves as fast as possible and thus repel the herbivore totally. For a young sapling, the capability of repelling the herbivore totally might thus be a feasible strategy whereas an older sapling may tolerate localised damage better and compensate for the damage within the undamaged plant parts.     

Wound-induced changes in the palatability of Betula pubescens and B. pendula

Summary Leaves of Betula were damaged artificially in April, June and August 1982. Palatability of damaged and adjacent undamaged leaves was assessed against controls in bioassays using the polyphagous Lepidoptera Spodoptera littoralis and Orgyia antiqua. Assessments were carried out at intervals from six hours to five months following each damage date. Palatability (relative proportions of leaves consumed) was significantly lower than controls in damaged and adjacent leaves after six hours and remained detectable for up to two months but this was less clear in the June-damaged samples and undetectable in the August group. Adjacent leaves were significantly affected whether distal or proximal to the damaged leaves. Marked and significant changes occurred in levels of soluble tannins in the damaged and adjacent leaves but the relationship between crude tannin levels and changed palatability was not simple cause and effect. No significant effects of damage on aphid (Euceraphis punctipennis) reproduction could be detected among birches in a growth room experiment in which half the trees were artificially damaged and half were controls. The results are discussed in the light of earlier work on induced defence in birch and five areas of significant new information represented by the results in this paper are identified. Spodoptera was reared under M.A.F.F. licence PHF 121/57     

Purification and Characterization of Assimilatory Nitrate Reductase from the Cyanobacterium Plectonema boryanum

Assimilatory nitrate reductase (NR) was solubilized by acetonetreatment from Plectonema boryanum and was purified 7,700-foldby heat treatment, ammonium sulfate fractionation and chromatographyon DEAE-Sephacel and Sephadex G-150. Purified NR had a specificactivity of 85 µmol NO₂^– formed min^–1 mg^–1protein. The enzyme retained both ferredoxin (Fd)- and methylviologen (MV)-linked NR activities throughout the purificationprocedure. Molecular weight was 80,000. The pH optimum was 10.5in the MV-assay and 8.5 when assayed with enzymatically reducedFd as the electron donor. Apparent Km values for nitrate andMV were 700 µM and 2,500µM in the MVassay and 55µM and 75 µM for nitrate and Fd in the Fd-assay.The enzyme was inhibited by thiol reagents and metal-chelatingreagents. (Received October 1, 1982; Accepted March 8, 1983)     

Nutrition and the ozone sensitivity of birch (Betula pendula)

 Cuttings of a single birch clone (Betula pendula) were grown in field fumigation chambers throughout the growing season in either filtered air (control) or 90/40 nl O₃ l^–1 (day/night). Both regimes were split into plants under high and low nutrient supply (macro- and micronutrients). The stomatal density of leaves was increased by ozone but was lowered at high nutrition, while the inner air space was hardly affected by the treatments. Ozone induced macroscopic leaf injury regardless of nutrition, but leaf shedding was delayed in the low-fertilized plants, despite O₃ uptake being similar to that in high-fertilized plants. The leaf turn-over was enhanced in the O₃-exposed high-fertilized plants, but length growth and leaf formation of stems were not affected by ozone in either nutrient regime. Leaves of high-fertilized plants showed O₃-caused decline in photosynthetic capacity, water-use efficiency, apparent carbon uptake efficiency and quantum yield earlier as compared with low-fertilized plants, whereas chlorophyll fluorescence (F_V/F_M) and leaf nitrogen concentration were rather stable. CO₂ uptake rate and rubisco activity of young leaves compensated for the O₃ injury in the ageing leaves of the low-fertilized plants. In 8-week-old leaves, however, the O₃-induced decline in CO₂ uptake did not differ between the nutrient regimes and was associated with increased dark respiration rather than changed photorespiration. The balance between CO₂ supply and demand was lost, as was stomatal limitation on CO₂ uptake. High nutrition did not help leaves to maintain a high photosynthetic capacity and life span under O₃ stress. Received: 6 July 1996 / Accepted: 4 June 1997     

Investigation of daily mitotic activity of the birch, Betula pendula Roth

A study was made of the daily mitotic activity in the seedling root meristem of birch trees growing in an ecologically clear area--the biological station of Voronezh State University "Venevitinovo". The peak of mitotic activity was exposed at 9 a. m. (according to winter time). The rise of mitotic index was noted at 9 and 12 p. m. due to an increase in the share of cells being in the prophase stage, and to a high number of dividing cells with persistent nucleoli. A possibility of prolongation of the mitotic cycle time is supposed to be due to cell delay in prophase stage, which may be associated with anthropogenic and nature-climatic influences on the original trees themselves and on their seed progeny. This makes it possible to consider the investigated region as only conventionally clear, because of the availability of a high recreative pressure upon the trees.     

Report of Quambalaria cyanescens in association with the birch (Betula pendula)

Long-term microbiological investigation of the pollen of silver birch (Betula pendula) in the Moscow and Moscow oblast areas revealed that almost one-third of the analyzed samples contained the fungus identified by morphological, cultural, and molecular genetic techniques as Quambalaria cyanescens (de Hoog & G.A. de Vries) Z.W. de Beer, Begerow & R. Bauer. This species was previously known mostly as a symbiont of tropical plants of the genera Eucalyptus and Corymbia and have not been isolated in Russia. We revealed a close association between Quambalaria cyanescens and silver birch. The micromycete was regularly detected in pollen samples, as well as on the inside and outside of the aments, and on the surface of leaves and branches. It was never isolated from other plant species in the investigated area. The data on the morphological and cultural characteristics of the fungus, its cell ultrastructure, and occurrence are presented, as well as the phylogenetic analysis of the isolated strains.     

Within-stand variation in silver birch (Betula pendula Roth) phenology

Key message

Within a local population genotypes differ in the timing of bud burst, but genotypes with early bud burst unfold their leaves slower, resulting in an equal period of carbon gain.

Abstract

The ability of local populations to cope with disturbances like adverse weather events or a changing climate depends on the genotypic richness of such populations, emphasising the importance of differences between genotypes in traits related to growth and survival at this scale. Due to their longevity, these differences are of special importance in trees, yet for trees, differences between genotypes within local populations remain unexplored. The phenological cycle is important in this respect, since a correct timing of phenological events is critical for growth and survival of trees, especially in environments with strong seasonality and changes in the timing of phenological events has consequences for, among others, net ecosystem productivity and the climate system as a whole. In this light accounting for differences in the timing of phenological events within species is currently identified as a research challenge. This study contributes to the knowledge of differences between genotypes on the small spatial scale of a local population. We examined the timing of phenological events of 15 micropropagated silver birch (Betula pendula Roth) genotypes representing a natural population. Measurements covered bud burst (7 years) and leaf unfolding in spring and chlorophyll degradation in autumn (2 years for both). These data were used to estimate the period of carbon gain. Differences between genotypes in the temperature sum required for bud burst were present, with genotypes showing ‘early’ (i.e. a low temperature sum requirement for bud burst) and ‘late’ bud burst across the 7-year study period. Differences were small in most years (i.e. 3 days), but differences of 16 days were recorded within the 7-year study period as well. Genotypes with ‘early’ bud burst were less sensitive to variations in environmental conditions in spring compared to genotypes with ‘late’ bud burst. Differences in bud burst were not carried over to the estimated period of carbon gain. Due to faster leaf expansion in genotypes with ‘late’ bud burst and the lack of differences between genotypes in autumn senescence the estimated period of carbon gain was similar among genotypes.     

Somatic embryogenesis in cell cultures of birch (Betula pendula Roth.)

Somatic embryogenesis was induced in cell cultures of birch (Betula pendula Roth.) derived from juvenile tissue of seed embryos and from mature leaf tissue. Embryos were formed in liquid and on solidified medium containing 2,4-dichlorophenoxyacetic acid (2,4-D) and 6-furfurylaminopurine (kinetin). Sometimes somatic embryos formed only after transfer to medium devoid of growth regulators. The embryos germinated on hormone-free medium and were potted in soil and grown in the greenhouse.Finnish Forest Research InstituteUniversity of Helsinki, School of Pharmacy;     

Comparisons of the efficiency of some promoters in silver birch (Betula pendula)

The efficiency of several promoters (pin2 from potato, ubiquitin from sunflower, rolC from Agrobacterium rhizogenes, act1 from rice and CaMV 35S from cauliflower mosaic virus) fused to the uidA reporter gene was measured after biolistic bombardment of birch leaves (Betula pendula L.). The highest level of β-glucuronidase (GUS) activity was achieved with the pin2 promoter and the lowest activity with the CaMV 35S promoter. The activity of the potato wound-inducible promoter (pin2) was also tested in stably transformed birch. The promoter showed induced activity after mechanical wounding and feeding by leaf weevils. The systemic effect was confirmed by enhanced GUS activity in non-wounded leaves. The results of this study indicated that the potato wound-inducible promoter maintains its function in birch and would be a suitable promoter in studies of insect-birch interaction at the molecular level. Received: 17 October 1996 / Revision received: 7 February 1997 / Accepted: 1 March 1997