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.     

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.     

Photosynthesis and Carbon Partitioning in Transgenic Tobacco Plants Deficient in Leaf Cytosolic Pyruvate Kinase

Whole-plant diurnal C exchange analysis provided a noninvasive estimation of daily net C gain in transgenic tobacco (Nicotiana tabacum L.) plants deficient in leaf cytosolic pyruvate kinase (PK_c−). PK_c− plants cultivated under a low light intensity (100 μmol m⁻² s⁻¹) were previously shown to exhibit markedly reduced root growth, as well as delayed shoot and flower development when compared with plants having wild-type levels of PK_c (PK_c+). PK_c− and PK_c+ source leaves showed a similar net C gain, photosynthesis over a range of light intensities, and a capacity to export newly fixed ¹⁴CO₂ during photosynthesis. However, during growth under low light the nighttime, export of previously fixed ¹⁴CO₂ by fully expanded PK_c− leaves was 40% lower, whereas concurrent respiratory ¹⁴CO₂ evolution was 40% higher than that of PK_c+ leaves. This provides a rationale for the reduced root growth of the PK_c− plants grown at low irradiance. Leaf photosynthetic and export characteristics in PK_c− and PK_c+ plants raised in a greenhouse during winter months resembled those of plants grown in chambers at low irradiance. The data suggest that PK_c in source leaves has a critical role in regulating nighttime respiration particularly when the available pool of photoassimilates for export and leaf respiratory processes are low.     

Loss of Photosynthetic Activity in Two Blue-Green Algae as a Result of Osmotic Stress

A progressive loss of photosynthetic activity occurred when cells of Anacystis nidulans and Coccochloris peniocystis were incubated in increasing concentrations of osmotica from 0.2 to 0.7 M, and there was a release of pteridine from the cells proportional to the loss of photosynthetic activity.     

Effects of Glycolate Pathway Intermediates on Glycine Decarboxylation and Serine Synthesis in Pea (Pisum sativum L.)

The study aimed to test the hypothesis that ammonia production by Rhizobium bacteroids provides not only a source of nitrogen for growth but has a central regulatory role in maintaining the metabolic activity and functional integrity of the legume nodule. Production of ammonia in intact, attached nodules was interrupted by short-term (up to 3 days) exposure of the nodulated root systems of cowpea (Vigna unguiculata L. Walp cv Vita 3: Rhizobium CB 756) and lupin (Lupinus albus L. cv Ultra: Rhizobium WU 425) to atmospheres of argon:oxygen (80:20; v/v). Treatment did not affect nodule growth, levels of plant cell and bacteroid protein, leghaemoglobin content, or nitrogenase (EC 1.7.99.2) activity (acetylene reduction) but severely reduced (by 90%) synthesis and export of the major nitrogenous solutes produced by the two symbioses (ureides in cowpea, amides in lupin). Glutamine synthetase (EC 6.3.1.2) and NAD:glutamate oxidoreductase (EC I.4.1.2) were more or less stable to Ar:O₂ treatment, but activities of the glutamine-utilizing enzymes, glutamate synthase (EC 2.6.1.53), asparagine synthetase (EC 6.3.5.4) (lupin only), and de novo purine synthesis (cowpea only), were all markedly reduced. Production and export of nitrogenous solutes by both symbioses resumed within 2 hours after transferring Ar:O₂-treated plants back to air. In each case the major exported product of fixation after transfer was initially glutamine, reflecting the relative stability of glutamine synthetase activity. Subsequently, glutamine declined and products of its assimilation became predominant consistent with resurgence of enzymes for the synthesis of asparagine in lupin and ureides in cowpea. Enzymes not directly involved with either ammonia or glutamine assimilation (purine synthesis, purine oxidation, and carbon metabolism of both bacteroids and plant cells) also showed transient changes in activity following interruption of N₂ supply. These data have been interpreted to indicate a far-reaching effect of the production of ammonia by bacteroids on a wide range of enzymes, possibly through control of protein turnover, rather than a highly specific effect of ammonia, or some product of its assimilation, on a few enzyme species.     

Acclimation to High CO(2) in Bean : Carbonic Anhydrase and Ribulose Bisphosphate Carboxylase

Young bean plants (Phaseolus vulgaris L. cv Seafarer) grew faster in air enriched with CO₂ (1200 microliters per liter) than in ambient CO₂ (330 microliters per liter). However, by 7 days when increases in overall growth (dry weight, leaf area) were visible, there was a significant decline (about 25%) in the leaf mineral content (N, P, K, Ca, Mg) and a drop in the activity of two enzymes of carbon fixation, carbonic anhydrase and ribulose 1,5-bisphosphate (RuBP) carboxylase under high CO₂. Although the activity of neither enzyme was altered in young, expanding leaves during the acclimation period, in mature leaves the activity of carbonic anhydrase was reduced 95% compared with a decline of 50% in ambient CO₂. The drop in RuBP carboxylase was less extreme with 40% of the initial activity retained in the high CO₂ compared with 50% in the ambient atmosphere. While CO₂ enrichment might alter the flow of carbon into the glycolate pathway by modifying the activities of carbonic anhydrase or RuBP carboxylase, there is no early change in the ability of photosynthetic tissue to oxidize glycolate to CO₂.     

Radiation injury of the plants in the zone of influence of the accident on Chernobyl Nuclear Power Station (NPS)

Were considered the radiobiological effects in some species of agricultural and wild growing plants in 30-kilometer zone of alienation of Chernobyl nuclear power station and other radionuclide contaminated territories. The particular attention was given to the distance plant reactions: immunity decreasing, genetic consequences, changes in phytocenosis. Was discussed the question of possibility of plant adaptation to conditions of high radiation influence.     

Estimating Photosynthesis and Concurrent Export Rates in C3 and C4 Species at Ambient and Elevated CO2

The ability of 21 C₃ and C₄ monocot and dicot species to rapidly export newly fixed C in the light at both ambient and enriched CO₂ levels was compared. Photosynthesis and concurrent export rates were estimated during isotopic equilibrium of the transport sugars using a steady-state ¹⁴CO₂-labeling procedure. At ambient CO₂ photosynthesis and export rates for C₃ species were 5 to 15 and 1 to 10 μmol C m⁻² s⁻¹, respectively, and 20 to 30 and 15 to 22 μmol C m⁻² s⁻¹, respectively, for C₄ species. A linear regression plot of export on photosynthesis rate of all species had a correlation coefficient of 0.87. When concurrent export was expressed as a percentage of photosynthesis, several C₃ dicots that produced transport sugars other than Suc had high efflux rates relative to photosynthesis, comparable to those of C₄ species. At high CO₂ photosynthetic and export rates were only slightly altered in C₄ species, and photosynthesis increased but export rates did not in all C₃ species. The C₃ species that had high efflux rates relative to photosynthesis at ambient CO₂ exported at rates comparable to those of C₄ species on both an absolute basis and as a percentage of photosynthesis. At ambient CO₂ there were strong linear relationships between photosynthesis, sugar synthesis, and concurrent export. However, at high CO₂ the relationships between photosynthesis and export rate and between sugar synthesis and export rate were not as strong because sugars and starch were accumulated.