Modelling the distribution of diameter growth along the stem in Scots pine

This paper presents an empirical model for the distribution of diameter growth along the stem in Scots pine (Pinus sylvestris L.) and for the consequent stem form over time. First, the distribution of annual mass growth in the stem is determined as a function of the total annual growth in stem mass, current stem mass and the distribution of the latter along the stem. Second, the distribution of diameter growth is obtained by converting the fraction of annual growth in the stem mass at a given height in the stem into the thickness of the annual ring at the same height. Application of the model to Scots pine data sets including both young and mature trees not used in parameter estimation showed that the model was capable of reconstructing the distribution of diameter growth from the stem butt to the apex and from the pith to the stem surface at any height in the stem in both young and mature trees. The resulting empirical model was also linked to a physiological, process-based model in order to study its performance in a simulated stand. Simulations representing trees grown in unthinned and thinned Scots pine stands with trees of different status (from dominant to suppressed) showed that the response in tree growth to thinning in terms of the distribution of diameter growth along the stem was quite realistic relative to measured data.     

Influence of avilamycin administration and its subsequent withdrawal on emergence and disappearance of antimicrobial resistance in enterococci in the intestine of broiler chickens

AIMS: To investigate the influence of avilamycin (AVM) administration and its subsequent withdrawal on the emergence and disappearance of AVM-resistant enterococci in the intestine of broiler chickens. METHODS AND RESULTS: Five chicks each of C, L and H groups were given the basal diet, the basal diet supplemented with 5 g AVM/ton and the basal diet supplemented with 50 g AVM/ton, respectively. The AVM-resistant Enterococcus faecalis population did not emerge during 30 days of the AVM administration period, whereas the AVM-resistant Enterococcus faecium with a minimum inhibitory concentration of >512 microg ml(-1) in the faeces of chicks of the L and H groups emerged on 3 and 1 days after the AVM administration, respectively. Thereafter, the AVM-resistant Ent. faecium population density in both L and H groups maintained high levels during the AVM administration period. Twenty days after the AVM withdrawal, the AVM-resistant Ent. faecium population disappeared from the intestines of both four of five chicks of L group and three of five chicks of H group. The AVM-resistant Ent. faecium population density in one chick from each of the groups, L and H, did not change before and after the AVM removal. CONCLUSIONS: The AVM-resistant Ent. faecium emerged during the AVM administration, and disappeared from the intestine of most chicks after the AVM withdrawal. However, the AVM-resistant Ent. faecium persisted in some chicks 20 days after AVM withdrawal. SIGNIFICANCE AND IMPACT OF THE STUDY: Our results suggest that introducing an AVM withdrawal period could minimize the risk of AVM-resistant Ent. faecium becoming carcass contaminants, and that prudent antibiotic use alone is not sufficient to stem emergence of the AVM-resistant Ent. faecium.     

Laboratory culture of Chironomus tentans for use in toxicity testing: optimum initial egg-stocking densities

The midge Chironomus tentans Fabricius is a commonly used freshwater invertebrate in sediment toxicity tests. Rigorous laboratory culturing techniques are needed to provide organisms of uniform quality and known age for use in testing and for the continuation of the culture itself. This study was conducted to determine the effect of initial culture stocking density on: (1) post-hatch (larval) dry weight, body length and head-capsule width at 10 and 20 days; (2) time to emergence; (3) number and sex of emergent adults; (4) number of larvae and pupae at test termination (day 42 post hatch); and (5) adult dry weight. Three egg stocking densities were used 690 (1.1 eggs cm^–2), 1043 (1.7 eggs cm^–2) and 1463 (2.4 eggs cm^–2). Mean weight of larvae at 10 days in high density tanks (0.13 mg/organism) was significantly higher (P=0.003) than both the medium and low density tanks (0.10 and 0.09 mg/organism, respectively). No significant differences between the three stocking densities were observed for the body length or head-capsule width at either 10 or 20 days post-hatch. Although not statistically significant, larval dry weight decreased with increased stocking density at day 20. A significantly (P=0.02) greater number of females (173±28) emerged from the low stocking density compared to both the medium and high stocking densities (123±45 and 118±54, respectively). Peak adult emergence for the low and medium stocking densities occurred between days 22 and 25 post-hatch, whereas peak adult emergence occurred between days 30 and 33 for the high stocking density. Survival relative to the initial number of eggs stocked was significantly greater (P=0.007) in the low density treatment compared to that in either the medium or the high density treatments. Mean adult weight exhibited an inverse relationship with initial stocking densities. At test end, there was not a significant difference in the mean number of organisms surviving and emerging in the three density levels. The central tendency for number of organisms surviving for all three treatments was 504 organisms per tank (0.82 organisms cm^–2). The results of this experiment suggest that an optimal egg stocking density of 1.0 egg cm^–2 (600 eggs/tank) be used with the feeding rate identified. This would ensure uniform larvae at the appropriate developmental stage (2nd–3rd instar) needed for toxicological research/testing (e.g. 10 days post-hatch), as well as producing sufficient emergence of males and females for future culture establishment.     

Growth Medium and Phosphorus Supply Affect Cluster Root Formation and Citrate Exudation by Lupinus albus Grown in a Sand/Solution Split-Root System

We examined cluster root formation and root exudation by white lupin (Lupinus albus L. cv. Kiev Mutant) in response to growth medium and phosphorus supply in a sand/solution split-root system. The split-root system consisted of a nutrient solution compartment and a siliceous sand compartment. Phosphorus was applied at 1 (low-P plants) or 50 (high-P plants) μM as KH₂PO₄ to the solution compartment and at 10, 50 or 250 mg P kg⁻¹ as hydroxyapatite (Ca-P) to the sand compartment. In contrast to the high-P plants, P concentration and P uptake in the low-P plants increased with increasing P supply to the sand compartment. The NaHCO₃-extractable P was lower in the rhizosphere of the low-P plants than the high-P ones. The proton extrusion rate by the solution-grown roots of the low-P plants was higher than that of the high-P plants at the early growth stage. For the low-P plants, the proportion of dry root biomass allocated to cluster roots was higher in the solution compartment than that in the sand compartment. The citrate exudation increased in the sand compartment and decreased in the solution compartment with time, showing a lack of synchronization in citrate exudation by two root halves grown in different media. The cluster root proportion and citrate exudation in both compartments decreased with increasing shoot P concentration. An additional experiment with no P added to either root compartment showed that the proportion of cluster roots was about 9% lower in the sand than solution compartments. The results suggest that cluster root formation and citrate exudation can be significantly affected by the root growth medium in addition to being regulated by shoot P status. More P can be exploited from sparingly available Ca-P by the low-P plants than the high-P ones due to greater citrate exudation under P deficiency.     

Transport of galectin-3 between the nucleus and cytoplasm. II. Identification of the signal for nuclear export

Galectin-3, a factor involved in the splicing of pre-mRNA, shuttles between the nucleus and the cytoplasm. Previous studies have shown that incubation of fibroblasts with leptomycin B resulted in the accumulation of galectin-3 in the nucleus, suggesting that the export of galectin-3 from the nucleus may be mediated by the CRM1 receptor. A candidate nuclear export signal fitting the consensus sequence recognized by CRM1 can be found between residues 240 and 255 of the murine galectin-3 sequence. This sequence was engineered into the pRev(1.4) reporter system, in which candidate sequences can be tested for nuclear export activity in terms of counteracting the nuclear localization signal present in the Rev(1.4) protein. Rev(1.4)-galectin-3(240-255) exhibited nuclear export activity that was sensitive to inhibition by leptomycin B. Site-directed mutagenesis of Leu247 and Ile249 in the galectin-3 nuclear export signal decreased nuclear export activity, consistent with the notion that these two positions correspond to the critical residues identified in the nuclear export signal of the cAMP-dependent protein kinase inhibitor. The nuclear export signal activity was also analyzed in the context of a full-length galectin-3 fusion protein; galectin-3(1-263; L247A) showed more nuclear localization than wild-type, implicating Leu247 as critical to the function of the nuclear export signal. These results indicate that residues 240-255 of the galectin-3 polypeptide contain a leucine-rich nuclear export signal that overlaps with the region (residues 252-258) identified as important for nuclear localization.     

Hormonal regulation of cotton ovule and fiber growth: Effects of bromodeoxyuridine,AMO-1618 and p-chlorophenoxyisobutyric acid

The effects of 5-bromo-2-deoxyuridine (BUdR, thymidine analogue), AMO-1618 (2-isopropyl-4-dimethylamino-5-methylphenyl-1-piperidine carboxylate methyl chloride), a growth retardant, and p-chlorophenoxyisobutyric acid (PCIB, an antiauxin) on growth (dry weight increase) and fiber development in unfertilized cotton (Gossypium hirsutum L.) ovules grown in vitro have been studied. BUdR (5 M) causes about 70% inhibition of fiber production, with little effect on ovule growth, if applied during the first 6 d of culture in the presence of GA₃ and IAA. AMO-1618, when used with GA₃ alone, causes only a small reduction in both dry weight and fiber production, but when used with IAA alone reduces both fiber production and dry weight, the effect on the latter being predominant. In the presence of both IAA and GA₃, AMO-1618 causes a small decrease in fiber production but a major decrease in dry weight. PCIB completely inhibits fiber growth but has little effect on dry weight, especially when GA₃ is present. These results indicate that GA₃ mainly promotes ovule growth while IAA is largerly responsible for fiber growth.Abbreviations AMO-1618 2-isopropyl-4-dimethylamino-5-methylphenyl-1-piperidine carboxylate methyl chloride - BUdR 5-bromo-2-deoxyuridine - GA₃ gibberellic acid - IAA indole-3-acetic acid - PCIB p-chlorophenoxyisobutyric acid - TFU total fiber units     

Natural populations of the Closterium ehrenbergii (Desmidiales, Chlorophyta) species complex in Nepal

Several natural populations of the Closterium ehrenbergii Meneghini ex Ralfs species complex were collected in Nepal, in October–December 1982. Water temperature and pH were also recorded. Clonal isolates from these populations were identified to one of four mating groups (H, I, J and M) by test crossing with standard mating-type strains of known mating groups. Groups H and M have smooth walled zygospores, while Groups I and J have scrobiculated zygospore walls. Several undetermined isolates were found in some population samples. In contrast to the previously reported population samples from Nepal, especially from dried soil samples, some of these populations appeared to be rather heavily loaded with mutations that are deleterious to the sexual cycle (i.e. sexual compatibility, zygospore formation and germination). By genetic analysis, a zygote maturation-defective mutation (zym) was detected. One reason for such a heavy genetic load was suggested to be that most population samples had been maintained exclusively by asexual reproduction for a long period in large lakes and nearby ponds, or left-over vegetative populations in paddy fields after other members entered into dormancy through sexual reproduction. The significance of studying such mutations at sexual gene loci is discussed in the light of speciation problems in microalgae.     

INHIBITION OF CHLORELLA (CHLOROPHYCEAE) GROWTH BY FATTY ACIDS, USING THE PAPER DISC METHOD1,2

Using the paper disc-agar plate method, a number of fatty and related acids have been tested for tested activity for inhibiting the growth of Chlorella pyrenoidosa Chick. Of the saturated acids, a peak in growth inhibiting activity wax observed in the C₇–C₁₂ range, where inhibition wax observed when solutions down to 0.02 M were applied to the discs. Most of the unsaturated acids tested showed greater inhibition than did the corresponding saturated acids. Acrylic acid showed detectable inhibition at 0.001 M concentration.