Ferric chelate reduction by sunflower (Helianthus annuus L.) leaves: influence of light, oxygen, iron-deficiency and leaf age

The presence of ferric chelate reducing activity in sunflower[Helianthus annuus L.) leaves has been studied by submergingleaf discs in a solution with Fe(III)-ethylenediaminetetra-acetate(FeEDTA), batho-phenanthroline disulphonate (BPDS) and vacuuminfiltration. The effect of different factors on the Fe(III)reduction rate was studied. Ferric reduction rate was about10-fold higher in the light than in darkness. The light effectwas greatly inhibited by 3-(3,4-dichloro-phenyl)-1,1-dimethylurea(DCMU), a photosystem II inhibitor. Several inhibitors of redoxsystems [cis-platinum (II) diamine dichloride (cis-platin),p-nitro-phenylacetate (p-NPA) and p-hydroxymercuribenzoic acid(pHMB)] decreased the FeEDTA reduction rate. The greatest inhibitionwas produced by the - SH group reagent pHMB (17% of control,in light). The FeEDTA reduction rate was much higher in theabsence of O₂ than with air or 100% O₂. Superoxide dismutase(SOD) decreased FeEDTA reduction with air in the light. Youngleaves reduced Fe(III)-chelate at a higher rate than did olderleaves. In iron-deficient plants, leaves did not exhibit enhancedferric chelate-reducing activity as was observed in roots. Itis suggested that at least two different redox systems or twostates of the same redox system work in the light and in darkness. Key words: Iron, leaves, plasma membrane-redox, light, oxygen level     

TheAdh genomic region ofDrosophila ambigua: Evolutionary trends in different species

Summary The study of individual genes is essential to a comprehensive understanding of genome evolution. The wealth of information on alcohol dehydrogenase (Adh) inDrosophila makes this gene particularly suitable for such analysis. We have characterized more than 4 kb of the genomicAdh region inDrosophila ambigua and compared this region toDrosophila mauritiana andDrosophila pseudoobscura. The presence of two genes,Adh and 3ORF (open reading frame), has been confirmed and some of their essential features have been inferred from primary structural analysis. Inter- and intraspecific comparisons have led us to support that both genes may have diverged from an ancient precursor. They appear to be evolving independently, and show a species-specific pattern. TheAdh in theobscura group species lacks amino acids three and four when compared to the species of themelanogaster group and has accumulated most of its amino acid replacements in the third exon. Neither characteristic is observed when any other group species are compared, which suggests that these may be particular features of the evolution of theobscura group. The 3ORF is highly conserved among the three species analyzed, although variability in the length of the third exon and the nucleotide substitution rate, which is much higher than inAdh, are worth noting. According to our data, both mutation/fixation rates and the distribution of mutations vary over time, which makes it difficult to predict the evolutionary dynamics of specific genome regions.     

Urinary eCG patterns in the mare during pregnancy

Blood and urine samples collected from 12 mares at frequent intervals from 25 to 210 d of pregnancy were analyzed for equine chorionic gonadotropin (eCG). Blood and urine samples were collected daily through two consecutive ovulatory periods from five cyclic mares for comparative purposes. Separate radioimmunoassays (RIA) were developed to detect eCG in the urine and plasma. A simple and quick commercial dipstick enzyme-linked immunospecific assay (ELISA), developed for eCG in the blood, was also utilized in this study to detect eCG in the urine. In the 12 pregnant mares, eCG concentrations in both the plasma and urine as detected by RIA rose significantly on Day 40, peaked by Day 60 and slowly dropped to low levels by Day 200. The dipstick ELISA appeared more reliable for eCG in the plasma than in the urine of the five pregnant mares tested. However, on peak days (50 to 60), both the plasma and urine tested positive in all five mares. Similar eCG profiles were observed when urine samples from seven of the mares were assayed in the dipstick ELISA and RIA. The highest percentage of mares (86%) were positive for eCG by ELISA between Days 65 and 85. The highest concentration of eCG in the urine as detected by RIA was observed between Days 55 and 90. ECG-like immunoactivity was not detected by the ELISA in the urine of cyclic mares, but the RIA showed variable patterns with increases in immunoactivity that could not be correlated with physiological events. In summary, eCG in urine follows a similar profile as the eCG in plasma of mares during their first trimester of pregnancy.     

Frequency of chromosome polymorphism for pericentric inversions and B-chromosomes in Spanish populations of Rattus rattus frugivorus

Inversion frequencies in chromosomes 16 and 18 and B-chromosome frequency have been studied in three populations of Rattus rattus frugivorus.In two of these, Cuenca and San Pedro del Pinatar, the frequencies of homozygous and heterozygous individuals do not differ significantly from the Hardy-Weinberg equilibrium for both chromosome pairs. By contrast, in the Vega de Granada population there are fewer heterozygous and more homozygous individuals than expected on the basis of the Hardy-Weinberg distribution, although the frequency distributions of karyotypes in these three populations are not significantly different.In relation to the B chromosome, the Cuenca and San Pedro populations have frequencies of B-carrying animals of 0.25 and 0.22 respectively, the Vega de Granada population of 0.80.     

Role of roots and shoots in the regulation of the Fe efficiency responses in sunflower and cucumber

Several experimental approaches were used to study the role of roots and shoots in the regulation of the Fe efficiency responses in the roots of Fe deficient plants of sunflower ( Helianthus annuus L., inbred line RHA 274) and cucumber ( Cucumis sativus L., cv. Burpee pickler). The presence of the shoot apex and the youngest leaves in sunflower and cucumber plants was not indispensable to the development of the responses. In split-root experiments with sunflower plants, with either one or two shoots obtained by grafting, different parts of the root system could receive different Fe additions. Roots growing in a medium without Fe developed Fe efficiency re-sponses even when the other part of the root system was growing with Fe. Also, the part of the root system that was growing in a medium with Fe, developed some Fe efficiency responses, although delayed and at a lower level as compared with the root without external Fe. The results are discussed in relation to the idea that the development of the responses in the roots is controlled not only by the Fe content in the root, but also by some information transmitted between parts of a root system that differ in their Fe nutritional status.     

Effect of potassium status on K+ (Rb)+ uptake and transport in sunflower roots

Young sunflower plants ( Helianthus annuus L. cv. Halcón), grown in nutrient solution at two K⁺ levels (0.25 and 2.5 m M ) were used to study the effect of K⁺ content in the root on uptake and transport of K⁺ to the exuding stream of decapitated plants. Roots of plants grown in low K⁺ gave higher exudation flux, higher K⁺ concentration in exudate and higher K⁺ flux than high K⁺ roots. After 6 h of uptake the K⁺ flux in low K⁺ roots was about three times that in high K⁺ roots. When the roots were kept in a nutrient solution in which Rb⁺ replaced K⁺, low K⁺ roots exuded much more Rb⁺ than K⁺ after the first 2 h, whereas high K⁺ roots exuded about similar amounts of K⁺ and Rb⁺. In intact plants grown at three different K⁺ levels (0.1, 1.0 and 10.0 m M ), there was an inverse relationship between the K⁺ level in the nutrient solution and the Rb⁺ accumulated in the roots or transported to the shoot. The results suggest that the transport of ions from xylem parenchyma to stele apoplast may be controlled by ions coming down from the shoot in sieve tubes.     

Karyology of theScorzonera (Compositae) species from the Iberian Peninsula

A karyological study of 15 taxa ofScorzonera L. from the Iberian Peninsula has been made. The chromosome numbers found inS. hispanica var.pinnatifida, S. baetica, S. reverchonii, S. angustifolia, S. laciniata var.calcitrapifolia and var.subulata (2n = 14) are new. Diploid cytotypes with 2n = 14 and 2n = 12 prevail, andS. hispanica var.crispatula is the only taxon which exhibits autopolyploidy (2n = 14, 28). x = 7 is considered to be the base chromosome number within the genus, with x = 6 being derived from it by translocation. This and detailed karyotype analyses allow to group the Iberian Peninsula species ofScorzonera into three groups.     

Determination of urinary thiamine by high-pressure liquid chromatography utilizing the thiochrome fluorescent method

A sensitive, reproducible, and specific method for the determination of urinary thiamine has been established. Unique to this method is the use of high-pressure liquid chromatography (HPLC) to separate the fluorescent thiamine derivative from interfering fluorescent compounds. Urine samples were passed through a Decalso cation-exchange column, washed with 0.5 M KCl to remove some interfering compounds, and eluted with 3.4 M KCl. The eluted thiamine was converted to the fluorescent derivative, thiochrome, by reaction with alkaline potassium ferricyanide. The reaction mixture was extracted with isobutanol and subjected to HPLC monitored by a fluorescent detector.Within-day and day-to-day coefficients of variation proved to be 2.5% and 1.2%, respectively. Recovery of added thiamine (range 0.04 to 2.0 μg/ml) averaged 99.9 ± 5.3%. The sensitivity of this method was 0.03 μg/ml.     

A respirometric method for characterising the organic composition and biodegradation kinetics and the temperature influence on the biodegradation kinetics, for a mixture of sludge and bulking agent to be co-composted

A respirometric method was set up to study kinetics of biological reactions involved in the treatment of organic wastes-sludge mixed with pine barks--by composting. Oxygen consumption rates of this type of mixture were monitored during 10-20 days, using a 10 l respirometric cell kept at constant temperature and moisture. Oxygen consumption kinetics were modelled and organic matter composition was characterised as biomass, easily-biodegradable, slowly-biodegradable and non-biodegradable organic matter. The influence of temperature on kinetics was tested. Results show that this respirometric method is a useful tool for the characterisation of solid organic matter biodegradability and for the modelling of the biological kinetics of the composting process.