Carbon and nitrogen partitioning in young nodulated pea (wild type and nitrate reductase-deficient mutant) plants exposed to NH4NO3

Carbon and nitrogen partitioning was examined in a wild-type and a nitrate reductase-deficient mutant (A317) of Pisum sativum L. (ev. Juneau), effectively inoculated with two strains of Rhizobium leguminosarum (128C23 and 128C54) and grown hydroponically in medium without nitrogen for 21 days, followed by a further 7 days in medium without and with 5 mM NH₄NO₃. In wild-type symbioses the application of NH₄NO₃ significantly reduced nodule growth, nitrogenase (EC 1.7.99.2) activity, nodule carbohydrates (soluble sugars and starch) and allocation of [¹⁴C]-labelled (NO₃⁻, NH₄⁺, amino acids) in roots. In nodules, there was a decline in amino acids together with an increase in inorganic nitrogen concentration. In contrast, symbioses involving A317 exhibited no change in nitrogenase activity or nodule carbohydrates, and the concentrations of all nitrogenous solutes measured (including asparagine) in roots and nodules were enhanced. Photosynthate allocation to the nodule was reduced in the 128C23 symbiosis. Nitrite accumulation was not detected in any case. These data cannot be wholly explained by either the carbohydrate deprivation hypothesis or the nitrite hypothesis for the inhibition of symbiotic nitrogen fixation by combined nitrogen. Our result with A317 also provided evidence against the hypothesis that NO₃⁻ and NH₄⁺ or its assimilation products exert a direct effect on nitrogenase activity. It is concluded that more than one legume host and Rhizobium strain must be studied before generalizations about Rhizobium /legume interactions are made.     

Regulation of chloroplastic carbonic anhydrase : effect of magnesium

It was previously reported that magnesium ion inhibited carbonic anhydrase (Bamberger and Avron 1975 Plant Physiol 56: 481-485). Studies with partially purified carbonic anhydrase from spinach (Spinacia oleracea L.) chloroplasts show that the effect was the result of the chloride counterion and not the magnesium ion. Enzyme activity was reduced 50% upon addition of 3 to 10 millimolar MgCl₂ or KCl while all additions of MgSO₄ between 0.3 and 10 millimolar were mildly stimulatory.     

Glyoxylate decarboxylation during photorespiration

At 25° C under aerobic conditions with or without gluamate 10% of the [1-¹⁴C]glycollate oxidised in spinach leaf peroxisomes was released as ¹⁴CO₂. Without glutamate only 5% of the glycollate was converted to glycine, but with it over 80% of the glycollate was metabolised to glycine. CO₂ release was probably not due to glycine breakdown in these preparations since glycine decarboxylase activity was not detected. Addition of either unlabelled glycine or isonicotinyl hydrazide (INH) did not reduce ¹⁴CO₂ release from either [1-¹⁴C]glycollate or [1-¹⁴C]glyoxylate. Furthermore, the amount of available H₂O₂ (Grodzinski and Butt, 1976) was sufficient to account for all of the CO₂ release by breakdown of glyoxylate. Peroxisomal glycollate metabolism was unaffected by light and isolated leaf chloroplasts alone did not metabolise glycollate. However, in a mixture of peroxisomes and illuminated chloroplasts the rate of glycollate decarboxylation increased three fold while glycine synthesis was reduced by 40%. Although it was not possible to measure available H₂O₂ directly, the data are best explained by glyoxylate decarboxylation. Catalase reduced CO₂ release and enhanced glycine synthesis. In addition, when a model system in which an active preparation of purified glucose oxidase generating H₂O₂ at a known rate was used to replace the chloroplasts, similar rates of ¹⁴CO₂ release and [¹⁴C]glycine synthesis from [1-¹⁴C]glycollate were measured. It is argued that in vivo glyoxylate metabolism in leaf peroxisomes is a key branch point of the glycollate pathway and that a portion of the photorespired CO₂ arises during glyoxylate decarboxylation under the action of H₂O₂. The possibility that peroxisomal catalase exerts a peroxidative function during this process is discussed.Abbreviations HEPES N-2-hydroxyethylpiperazine-N-2-ethanesulphonic acid - INH isonicotinylhydrazide - PHMS pyridyl-2-yl--hydroxymethane sulphonic acid     

The effect of osmotic stress on the oxidation of glycolate by the blue-green alga Anacystis nidulans

Planta - Anacystis nidulans Richt. was shown to assimilate glycolic acid, and uptake was light-stimulated. In the dark 90% of the glycolate taken up was oxidised to CO2. Both light and dark uptake...     

Molecular and cellular aspects of development of arbuscular mycorrhizal symbiosis and its role in plant life

Development of arbuscular mycorrhizal (AM) symbiosis with plant root system in term of molecular and cellular events have been analysed. A role of AM symbiosis in plant life has been discussed. Molecular methods for analysis of arbuscular mycorrhizal fungi have been described.     

Problems faced by food-caching corvids and the evolution of cognitive solutions

The scatter hoarding of food, or caching, is a widespread and well-studied behaviour. Recent experiments with caching corvids have provided evidence for episodic-like memory, future planning and possibly mental attribution, all cognitive abilities that were thought to be unique to humans. In addition to the complexity of making flexible, informed decisions about caching and recovering, this behaviour is underpinned by a motivationally controlled compulsion to cache. In this review, we shall first discuss the compulsive side of caching both during ontogeny and in the caching behaviour of adult corvids. We then consider some of the problems that these birds face and review the evidence for the cognitive abilities they use to solve them. Thus, the emergence of episodic-like memory is viewed as a solution for coping with food perishability, while the various cache-protection and pilfering strategies may be sophisticated tools to deprive competitors of information, either by reducing the quality of information they can gather, or invalidating the information they already have. Finally, we shall examine whether such future-oriented behaviour involves future planning and ask why this and other cognitive abilities might have evolved in corvids.     

Chronic low doze ionizing irradiation and polyfactors of adaptation

The analysis of cytogenetic anomaly dynamics in conditions of chronic low doze effect of ionizing irradiation in generations of genetically homogeneous laboratory line of mice CC57W/Mv and genetically heterogeneous populations of vole's species, trapped in alienation zone of Chernobyl's NPP in places with different levels of radio nuclide contamination in 1994-2001 was carried out. The data about the physiological adaptation to ionizing irradiation effects under age of linear mice and non-linearity of frequency changes of separate cytogenetic anomalies in generations as laboratory line of mice, and genetically heterogeneous populations of vole's species were obtained. Was supposed, that the number of non-linear effects of the ionizing irradiation in low doze range could be stipulated by comparability between the intensity of it's damage effects and the activation by it the polyfactor systems of anti oxidant ones, reparation events, and also elimination of defective cells.     

Diel patterns of leaf C export and of main shoot growth for Flaveria linearis with altered leaf sucrose-starch partitioning

Diel C export from source leaves of two Flaveria linearis lines [85-1: high cytosolic fructose-1,6-bisphosphatase (cytFBPase) and 84-9: low cytFBPase] were estimated using three methods, including leaf steady-state (14)CO(2) labelling, leaf metabolite analysis, and leaf dry mass analysis in conjunction with leaf CO(2) exchange measurements. Synthesis and accumulation of starch during the daytime were much higher in 84-9. Relative (14)C-export (export as a % of photosynthesis) in the light was 36% higher in 85-1. The diel export patterns from (14)C-analyses correlated with those based on metabolite or dry weight/gas exchange analyses during the daytime, but not during the night. Night-time export estimated from (14)C-disappearance was 3.6 times lower than those estimated using the other methods. Even though the starch degradation at night was greater for 84-9, night-time export in 84-9 was similar to 85-1, since 84-9 showed both higher respiration and accumulation of soluble sugars (i.e. glucose) at night. Patterns of (14)C allocation to sink organs were also different in the two lines. Main stem growth was less in 84-9, being reduced most in the light when leaf export was lower relative to 85-1. Supplementation with sucrose for 1 h daily via the roots at a time when leaf export in 84-9 was low relative to 85-1 increased the stem growth rate of 84-9 to a level similar with that of 85-1. This study provides evidence that diel C availability predicted by source strength (e.g. C-export rate) influences main stem extension growth and the pattern of sink development in F. linearis.     

Structural architectonics of apical root meristems in coherence with the quantitative assessment of its damage by radiation

The dose dependencies of the aberrant anaphases frequency in the root meristem in 48 hours after irradiation in the range of doses of 4-10 Gy is characterized by threshold and plateau at 33% aberrant anaphase. The plateau indicates the activation of the recovery processes. Topology of cell rows in the primary meristem of the dose to 8 Gy are conserved and recovered damages. New cell rows are formed by local cell pools in the distal meristem, pericycle cells and subepidermy. It grows by intrusive character displacing the rows of damaged cells. Apparently the competition between clones of normal and aberrant cells plays the primary role in the mechanisms of recovery. Resulting to competition the promotion of aberrant cells to the extension zone is slowed down or blocked. So critical level of damage of the root apical meristem was defined about 50% of aberrant anaphase. Exceeding of this level leads to lethal consequence for meristem and it is accompanied by the inclusion of more radical process of restoration through regeneration. Regeneration leads to complete replacement of the apex tissues including the extension zone.