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.     

A study of the control of glycolate excretion in chlorella

Chlorella pyrenoidosa cells grown on 5% CO(2) excreted glycolate when incubated in light with 10 mm bicarbonate, but excreted no glycolate under the same conditions when they were maintained on air for 7 hours prior to the assay. Incubation of 5% CO(2)-grown and air-grown cells with 10 mm isonicotinyl hydrazide or 10 mm alpha-hydroxypyridinemethane sulfonate during the assay stimulated the excretion of glycolate by CO(2)-grown cells severalfold that of air-grown cells.Adaptation of CO(2)-grown Chlorella to growth on air did not affect the levels of glycolate dehydrogenase in the cells and did not affect the rate of dark oxidation and metabolism of exogeneous (14)C-glycolate by the cells. These results indicate that the lack of glycolate excretion by air-grown or air-adapted cells of Chlorella cannot be explained by a concomitant change in the level of glycolate dehydrogenase.     

Parents and offspring in an evolutionary game: the effect of supply on demand when costs of care vary

Current models of parent-offspring communication do not explicitly predict the effect of parental food supply on offspring demand (ESD). However, existing theory is frequently interpreted as predicting a negative ESD, such that offspring beg less when parental supply is high. While empirical evidence largely supports this interpretation, several studies have identified the opposite case, with well-fed offspring begging more than those in poorer condition. Here, we show that signalling theory can give rise to either a negative or a positive ESD depending on the precise form of costs and benefits. Introducing variation among parents in the cost of care, we show that the ESD may change sign depending upon the quantitative relation between two effects: (i) decreased supply leads to increased begging because of an increase in marginal fitness benefit of additional resources to offspring, (ii) decreased supply leads to reduced begging because it is associated with a decrease in parental responsiveness, rendering begging less effective. To illustrate the interplay between these two effects, we show that Godfray's seminal model of begging yields a negative ESD when care is generally cheap, because the impact of supply on the marginal benefits of additional resources then outweighs the associated changes in parental responsiveness to begging. By contrast, the same model predicts a positive ESD when care is generally costly, because the impact of care costs on parental responsiveness then outweighs the change in marginal benefits.     

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.     

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.     

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.