Photosynthesis,water use and growth of a C4 grass stand at high CO2 concentration

Leaf photosynthesis rate of the C₄ species Paspalum plicatulum Michx was virtually CO₂-saturated at normal atmospheric CO₂ concentration but transpiration decreased as CO₂ was increased above normal concentrations thereby increasing transpiration efficiency. To test whether this leaf response led growth to be CO₂-sensitive when water supply was restricted, plants were grown in sealed pots of soil as miniature swards. Water was supplied either daily to maintain a constant water table, or at three growth restricting levels on a 5-day drying cycle. Plants were either in a cabinet with normal air (340 mol (CO₂) mol^-1 (air)) or with 250 mol mol^-1 enrichment. Harvesting was by several cycles of defoliation.With abundant water supply high CO₂ concentration did not cause increased growth, but it did not cause an increase in growth over a wide range of growth-limiting water supplies either. Only when water supply was less than 30–50% of the amount used by the stand with a water-table was there evidence that dry weight growth was enhanced by high CO₂. In addition, with successive regrowth, the enhancing effect under a regime of minimal water allocations, became attenuated. Examination of leaf gas exchange, growth and water use data showed that in the long term stomatal conductance responses were of little significance in matching plant water use to low water allocation; regulation of leaf area was the mechanism through which consumption matched supply. Since high CO₂ effects operate principally via stomatal conductance in C₄ species, we postulate that for this species higher CO₂ concentrations expected globally in future will not have much effect on long term growth.     

Diffusion of inorganic carbon across an unstirred layer: a simplified quantitative approach

Abstract The quantitative approach used here is based on a model comprising a well-stirred medium, an unstirred layer, and a CO₂ absorbing leaf. The unstirred layer is divided up by planes into a number of sub-layers. Within each plane the concentration of each solute is everywhere the same as is the electric potential. These variables constitute the basic data. Thus the planes were characterized by their pH value. An equation is derived which enables the calculation of the basic data of a plane from the known data of another plane. In this way it is possible to calculate the basic data for all planes. From these data the rate of assimilation, the thickness of the unstirred layer and its sub-layers, the fluxes across the sub-layers and the conversions among the carbon components can be estimated. The CO₂ flux decreases, and the HCO^?₃ flux increases towards the leaf. There are negative fluxes of OH^& and CO^2–₃. H⁺ fluxes are of minor importance and can be ignored if the pH of the medium is higher than 8.0, provided no non-inorganic C buffers with appropriate pK_a are present. The significance of the carbon diffusion facilitating effect of an inorganic carbon system is expressed in various ways. The values obtained represent maxima, as the assumption is made that the equilibrium reactions are very fast. It is argued that even better effects are possible if the back-diffusion of CO^2–₃ could be prevented by lowering the pH of the unstirred layer.     

CO2 uptake and transport in leaf mesophyll cells

Abstract The acquisition of inorganic carbon for photosynthetic assimilation by leaf mesophyll cells and chloroplasts is discussed with particular reference to membrane permeation of CO₂ and HCO^?₃. Experimental evidence indicates that at the apoplast pH normally experienced by leaf mesophyll cells (pH 6–7) CO₂ is the principal species of inorganic carbon taken up. Uptake of HCO^?₃ may also occur under certain circumstances (i.e. pH 8.5), but its contribution to the net flux of inorganic carbon is small and HCO^?₃ uptake does not function as a CO₂-concentrating mechanism. Similarly, CO₂ rather than HCO^?₃ appears to be the species of inorganic carbon which permeates the chloroplast envelope. In contrast to many C₃ aquatic plants and C₄ plants, C₃ terrestrial plants lack specialized mechanisms for the acquisition and transport of inorganic carbon from the intercellular environment to the site of photosynthetic carboxylation, but rely upon the diffusive uptake of CO₂.     

Quantitative field investigations of feeding and territorial behaviour of young-of-the-year brook charr,Salvelinus fontinalis

Synopsis Direct observations of young-of-the-year brook charr, Salvelinus fontinalis, in a second-order woodland stream indicated that most of their feeding effort was directed toward sub-surface, drifting prey (83% of feeding time). Feeding from the substrate and water surface was much less frequent (17% of feeding time). Comparisons of gut contents to drift net and substrate fauna samples corroborated that the most commonly consumed prey (chironomid and trichopteran larvae, ostracods, and ephemeropteran nymphs) were captured primarily from sub-surface, invertebrate drift. The disproportionate numbers of some prey species in the guts of several fish indicate that some prey selection occurred. Territories appeared to be cardioid-shaped, and were often contiguous, with dominance hierarchies evident among the residents. Agonistic interactions were frequent. Charges and chases predominated (91% of interactions) while lateral displays were infrequent (9% of interactions). Overall, these fish spent most of the daylight hours station-holding (77%) and feeding (18%). While only 3% of total time was spent in aggression, this amounted to 14% of the time a fish spent away from its station. There was some indication that territories were defended at a cost of feeding time.     

Enzymes metabolizing dimethylamine, trimethylamine and trimethylamine N-oxide in the yeast Sporopachydermia cereana grown on amines as sole nitrogen source

Abstract Sporopachydermia cereana , an ascosporogenous yeast, grew on dimethylamine, trimethylamine or trimethylamine N -oxide as sole nitrogen sources and produced mono-oxygenases for dimethylamine and trimethylamine that were significantly more stable than the corresponding enzymes found in Candida utilis . No trimethylamine mono-oxygenase activity was found in S. cereana grown on dimethylamine. In cells grown on trimethylamine N -oxide (but not on the other nitrogen sources), evidence for an enzyme metabolizing the N -oxide, possibly an aldolase, but more probably a reductase was obtained. All these activities showed a similar requirement for the presence of FAD or FMN in the extract buffer during isolation to retain activity. Amine mono-oxygenase activities showed a similar sensitivity to inhibitors, including proadifen hydrochloride and carbon monoxide as the corresponding enzymes in C. utilis . The trimethylamine N -oxide-dependent oxidation of NADH was more sensitive to inhibition by EDTA, N -ethylmaleimide and β-phenylethylamine than the mono-oxygenases, and less sensitive to KCN, and activity was significantly higher with NADPH than was observed with the 2 mono-oxygenases.     

Cycling of soil carbon in a Japanese red pine forest II. Changes occurring in the first year after a clear-felling

Cycling of soil carbon in the first year after a clear-felling was compared with that before the felling in a Japanese red pine forest in Hiroshima Prefecture, west Japan. The daily mean temperature at the soil surface in summer was increased after the felling in comparison to that before felling, and the water content of both the A₀ layer and the surface mineral soil was decreased due to the loss of the forest canopy. The rate of weight loss of the A₀ layer was reduced after felling. However, accumulation of the A₀ layer rapidly decreased because of the lack of litter supply to the forest floor. Low soil respiration after felling was mainly caused by the cessation of root respiration. Analysis of annual soil carbon cycling was then conducted using a compartment model. The relative decomposition rate of the A₀ layer decreased whereas that of humus and dead roots in mineral soil increased to some extent after felling. The accumulation of carbon in mineral soil, however, increased slightly due to the supply of humus from roots killed by the felling.     

The heterogeneity of arylhydrocarbon hydroxylase in fetal liver microsomes of rats

The characteristic of arylhydrocarbon hydroxylase system in fetal liver microsomes of rat was investigated. NADH-synergistic effect on NADPH-dependent arylhydrocarbon hydroxylase was observed in fetal liver microsomes of rat but not in maternal liver microsomes. NADH-synergistic effect decreased in parallel with the decrease of the ratio of cytochrome b5/cytochrome P-450 in liver microsomes. The cytochrome P-450 in arylhydrocarbon hydroxylase system in fetal liver microsomes of rat seemed to be different from that in offspring liver microsomes in respect of its dependency on cytochrome b5 system for its maximum activity.     

The enzymatic determination of bicarbonate and CO2 in reagents and buffer solutions

A method for the determination of bicarbonate in buffer solutions between pH 7.5 and 8.75 and in stock solutions of NaHCO3 is described. The HCO-3 is reacted with phosphoenolpyruvate (PEP) in the presence of PEP carboxylase (EC 4.1.1.31) and the oxaloacetate formed reduced to malate by NADH in the reaction catalyzed by malate dehydrogenase (EC 1.1.1.37). The extent of oxidation of NADH is measured spectrophotometrically. Experiments using standard solutions show that 1 mol of NADH is oxidized per mol of HCO-3 added. The method was used to establish the precautions needed to prepare buffer solutions containing less than 1% of the bicarbonate which would be present in the same buffers in equilibrium with air.     

分子氮影响下的蓝藻Anabaena7120乙炔还原

经分子氮预处理的蓝藻乙炔还原活性下降。分子氮对乙炔还原的抑制作用可因CO_2的加入而削弱,氮浓度增高时,CO_2的此种有益作用即消失。在5％ CO_2条件下:(1)光照强度大时,经分子氮预处理的蓝藻乙炔还原活性比未经处理的(氮气中)高些,弱光下则削弱,暗中削弱更大;(2)它受到光合抑制剂的抑制较大;(3)对CO_2和O_2的敏感度比未经氮预处理者小;(4)分子氢对其支持与来经氮预处理的相差甚微,但对其受O_2损伤时的保护作用则大些;(5)MSX对分子氮预处理的蓝藻乙炔还原也有明显的抑制,且比单加CO_2的大。     

Platelet activating factor (PAF) production by mouse embryos in vitro and its effect on embryonic metabolism

Factors affecting the production of platelet activating factor (PAF) by mouse embryos during culture in vitro were investigated. Detectable levels of embryo-derived PAF were produced within 1-4 hr with maximum PAF activity being observed after 6 hr of culture in vitro. The amount of PAF detected in media after 24 hr of culture of two-cell embryos was equivalent to 12.8 ng PAF/embryo. However, differences in activity were apparent with increased time in culture. Reduced synthesis of PAF during culture in vitro was supported by the observation that morulae stage embryos collected fresh from the reproductive tract displayed more PAF activity than morulae resulting from the 48 hr culture of two-cell embryos. In addition to determining production characteristics of PAF by embryos, we also show that the production of CO2 from carbon-1 position of lactate is positively correlated with the ability of embryos to develop during subsequent culture in vitro and therefore could be used as a measure of embryo viability. Furthermore, culture of embryos in media supplemented with PAF resulted in an increase in lactate utilization demonstrating a direct effect of PAF on the embryo. As PAF is produced by preimplantation embryos, an autocoid role of PAF in regulating embryo development is implicated. Therefore, the reduced production of PAF by embryos in vitro may explain the decreased viability of embryos commonly observed following their culture in vitro.