Transformations in soil and availability to plants of15N applied as inorganic fertilizer and legume residues

Summary A pot experiment was conducted to study the transformations of organic and inorganic N in soil and its availability to maize plants. Inorganic N was in the form of¹⁵N labelled ammonium sulphate (As) and¹⁵N labelledSesbania aculeata (Sa), a legume, was used as organic N source. Plants utilized 20% of the N applied as As; presence of Sa reduced the uptake to 14%. Only 5% of the Sa-N was taken up by the plants and As had no effect on the availability of N from Sa. Losses of N from As were found to be 40% which were reduced to 20% in presence of Sa. Losses of N were also observed from Sa which increased in the presence of As. Application of As had no effect on the availability of soil or Sa-N. However, more As-N was transported into microbial biomass and humus components in the presence of Sa.Plants derived almost equal amounts of N from different sourcesi.e., soil, Sa and As. However, more As-N was transported into the shoots whereas the major portion of nitrogen in the roots was derived from Sa.     

Is organic acid required for nutrition of thermophilic fungi?

In contrast to a published report [Wali et al. Arch Microbiol 118:49–53 (1978)], an organic acid is not essential for the growth of thermophilic fungi. The thermophilic fungus, Thermomyces lanuginosus, grows satisfactorily in a synthetic medium containing glucose as carbon source if the pH of the medium is controlled. The control of pH is essential for the concentration of carbon dioxide in the growth medium and the activity of anaplerotic enzyme, pyruvate carboxylase.Abbreviations PEP phosphoenolpyruvate - GDP guanosine 5-diphosphate     

Dietary niacin requirement of fingerling Channa punctatus (Bloch)

A 16‐week experiment was accomplished to determine the dietary niacin requirement of fingerling Channa punctatus (6.8 ± 0.92 cm; 4.65 ± 0.46 g) by feeding seven casein‐gelatin based isonitrogenous (450 g/kg CP) and isoenergetic (18.39 kJ/g GE) diets with graded levels of niacin (0, 10, 20, 30, 40, 50 and 60 mg/kg diet) twice a day to apparent satiation to triplicate groups of fish. Significantly best absolute weight gain (AWG; 38.19 g/fish), feed conversion ratio (FCR; 1.42) and protein retention efficiency (PRE; 26.47%) were registered in fish fed 40 mg niacin/kg diet. Also, fish fed above diet exhibited maximum carcass protein. Hemoglobin (Hb), RBCs counts and hematocrit (Hct) were improved with the incremental levels of dietary niacin up to 40 mg/kg. However, liver niacin content showed the positive correlation up to 50 mg/kg niacin and then leveled off. Fingerling C. punctatus fed niacin‐free diet showed retarded growth, poor feed utilization, high mortality, difficult motion and skin haemorrhage. Broken‐line regression analysis of AWG, FCR and PRE indicated that fingerling C. punctatus require niacin in the range of 37.1–42.1, whereas that of liver niacin concentration indicated the niacin requirement at 52.3 mg/kg dry diet.     

Chill-responsive dehydrins in blueberry: Are they associated with cold hardiness or dormancy transitions?

To survive winters, woody perennials of temperate zones must enter into endodormancy. Resumption of spring growth requires sufficient exposure to low temperature (chill units, CUs) in winter (chilling requirement), which also plays a role in the development of cold hardiness (cold acclimation). Physiological studies on dormancy breaking have focused on identifying markers, such as appearance or disappearance of proteins in response to varying degrees of chill unit accumulation. However, whether these changes are associated with dormancy transitions or cold acclimation is not clear. In the present study, greenhouse-grown blueberry (Vaccinium section Cyanococcus) plants were used to address this question. Three blueberry cultivars, Bluecrop, Tifblue, and Gulfcoast having chilling requirement of approximately 1 200, 900 and 600 CUs, respectively, were first exposed to 4°C for long enough to provide chill units equivalent to one-half of their respective chilling requirement. This treatment was expected to result in cold acclimation. A fraction of plants was then subjected to a 15/12°C (light/dark) regime for 2 weeks, a treatment expected to be “dormancy-neutral” but cause deacclimation. Before and after each treatment, cold hardiness and dormancy status of floral buds were determined; proteins were extracted from the buds collected on the same sampling date, and separated by one-dimensional SDS-PAGE. Dehydrin-like proteins were identified by immunoblotting, using anti-dehydrin antiserum. Results indicate that the chilling treatment resulted in cold acclimation as indicated by increased bud hardiness in all three cultivars. Data also indicate a distinct accumulation of three dehydrin-like proteins of 65, 60, and 14 kDa during cold acclimation. The cold hardiness and levels of dehydrin proteins decreased during the exposure to 15/12°C for 2 weeks. Results also confirmed that this treatment had no negative effect on chill unit accumulation. Densitometric scans of protein gels indicated a close association between the abundance of dehydrins and degree of cold hardiness in these cultivars. In addition, levels of the dehydrin proteins and cold hardiness remained about the same between 100% and >100% satisfaction of chilling requirement. These results suggest that changes in dehydrin expression are more closely associated with cold hardiness than with dormancy transitions.     

SELENIUM: AN ESSENTIAL ELEMENT FOR GROWTH OF THE COASTAL MARINE DIATOM THALASSIOSIRA PSEUDONANA (BACILLARIOPHYCEAE)1,2

An obligate requirement for selenium is demonstrated in axenic culture of the coastal marine diatom Thalassiosira pseudonana (clone 3H) (Hust.) Hasle and Heimdal grown in artificial seawater medium. Selenium deficiency was characterized by a reduction in growth rate and eventually by a cessation of cell division. The addition of 10⁻¹⁰ M Na₂eO₃ to nutrient enriched artifical seawater resulted in excellent growth of T. pseudonana and only a slight inhibition of growth occurred at Na₂SeO₃ concentrations of 10⁻³ and 10_-2 M. By contrast, Na₂SeO₄ failed to support growth of T. pseudonana when supplied at concentrations less than 10⁻⁷ M and the growth rate at this concentration was only one quarter of the maximum growth rate. The addition of 10⁻³ and 10⁻² M Na₂SeO₄ to the culture medium was toxic and cell growth was completely inhibited. Eleven trace elements were tested for their ability to replace the selenium requirement by this alga and all were without effect. In selenium-deficient and selenium-starved cultures of T. pseudonana cell volume increased as much as 10-fold as a result of an increase in cell length (along the pervalvar axis) but cell width was constant. It is concluded that selenium is an indispensable element for the growth of T. pseudonana and it should be included as a nutrient enrichment to artificial seawater medium when culturing this alga.     

Dormancy release in Pinus sylvestris L. and Picea abies (L.) Karst. seedlings: effects of intermittent warm periods during chilling

Summary Experiments designed to test three simulation models were used to study the effects of intermittent warm periods during the chilling period on dormancy release in 2-year-old seedlings of Pinus sylvestris L. and Picea abies (L.) Karst. The effect of the intermittent period varied according to its timing. Compared with corresponding continuous chilling treatments, the intermittent periods (1) after 1–3 weeks of chilling increased the proportion of the seedlings for which dormancy was subsequently released, and (2) after 4–7 weeks of chilling substantially diminished this proportion. The intermittent periods did not affect the time required for growth initiation in forcing conditions. These results support a simulation model with a strict end-point for the rest period. On the basis of the experimental results, division of the dormant period into three sub-periods is proposed.     

Gametic differentiation in Chlamydomonas reinhardtii: light dependence and gene expression patterns

Gametes of Chlamydomonas reinhardtii synthesize numerous proteins not observed in vegetative cells and vice versa. Gametogenesis induced changes in gene expression were confirmed by SDS-PAGE of in vitro translation products using total RNA from gametes and vegetative cells. Vegetative cells and gametes thus represent two cell types with distinct patterns of gene expression. The generation of mature gametes from liquid cultures of asynchronously growing vegetative cells was dependent on light. This light requirement could not be substituted for by an organic source of energy and carbon, indicating that light serves as a signal in gametogenesis. The light signal was shown to become effective only after preincubation in nitrogen-free medium. This delayed competence for light indicates that the two external signals — nitrogen-starvation and light —may function in sequence. Execution of the light dependent step in gamete formation required cytoplasmic protein synthesis and RNA synthesis.Abbreviations CAM chloramphenicol - DCMU 3-(3,4-dichlorophenyl)-1,1-dimethylurea - PSII photosystem II - TAP Tris acetate phosphate - TMP Tris minimal phosphate This paper is dedicated by C. F. Beck to Professor John L. Ingraham, teacher and friend, on the occasion of his 65th birthday     

A comparative study on nutrient cycling in wet heathland ecosystems

Summary The term relative nutrient requirement is introduced in order to measure and to compare the nutrient losses from different perennial plant populations and the amount of nutrient that they need to absorb to compensate these losses. The relative nutrient requirement (L) is defined as the amount of the growth-limiting nutrient that must be taken up to maintain or replace each unit of biomass during a given time interval (e.g., mgN g^-1 biomass year^-1). It is derived that in a plant community with two competing perennial plant populations, species¹ will become dominant if the relative competition coefficient k ₁₂ (sensu De Wit 1960) exceeds the ratio between the relative nutrient requirements of the two species (L ₁/L ₂), whereas species 2 will become dominant, if k ₁₂ is below this critical ratio. The above-ground litter production was measured inwet heathland communities dominated by Erica tetralix or by Molinia caeruleain order to estimate N and P losses from theaboveground biomass and to calculate the relative N and P requirements of these species. Molinia lost during one year 63% and 34%, respectively, of the amount of N and P present in the above-ground biomass at the end of the growing season. These losses were in Erica 27% and 31%, respectively. The relative N requirements of the two species show the same difference: 7.5 and 2.6 mg N g^-1 yr^-1, respectively, in Molinia and in Erica. Also the relative P requirement of Molinia is higher as well as that of Erica (0.18 versus 0.08 mg P g^-1 yr^-1). The relative competition coefficient of Molinia with respect to Erica (k _me ) is equal to unity under unfertilized conditions but increases with increasing nutrient supply. Under nutrient-poor conditions k _me is below the critical ratio of the relative nutrient requirements of the two species (L _m /L _e =2.9 or 2.3), so that Erica will be the dominant species. After an increase in nutrient availability k _me increases and exceeds this critical limit which results in Molinia replacing Erica. During the last 20 years this replacement of Erica-dominant communities by monocultures of Molinia has been observed in almost all wet heathlands in The Netherlands along with a strong increase in nitrogen availability.     

Evaluation of serum parameters relevant to vitamin D status in tamarins

Serum levels of 25(OH)D, alkaline phosphatase (AP), and parathormone (PTH) were evaluated to investigate the vitamin D requirement of Saguinus fuscicollis. Diets with various vitamin D content were fed 4 weeks and longer. The values of 25(OH)D (30-300 nmol/l), AP (less than 300 U/l), and PTH (less than or equal to 1,000 equl/l) considered as normal were obtained with 2,000 IU D3/kg diet, or 33 IU/animal/day, which we regard as the level required. Animals depleted of vitamin D for 215 days developed a secondary hyperparathyroidism.