Relationship between the concentration of sugars in the roots and VA mycorrhizal infection

Summary The VA-infected wheat varieties showed an increase of total (Lozano var.) and reducing (Lozano and Pane vars.) sugars in their root extracts. However, no clear relationship between sugar concentration in the root and VA mycorrhizal infection level could be established.In addition, the VA mycorrhizal hosts sorghum, alfalfa, sunflower and maize, and non-host radish and cabbage plants were tested for sugar content in their root extracts after fifteen days of growth. Sugars present in the root extracts of these plants did not seem to be a decisive factor in plant susceptibility to VA infection.     

The glands of Tamarix aphylla: a system for salt recretion or for carbon concentration?

During periods of high atmospheric humidity, twigs of Tamarix aphylla (L.) Karst. become covered by an alkaline solution. The pH of that solution fluctuates between 8.0 – 8.5 in the dark and 10.5 during the light hours. Such a solution, produced by the glands, constitutes an efficient trap for atmospheric CO₂. Upon the periodic drop in pH, much of the preabsorbed carbon may gradually be released from the solution. This enriches the immediate surroundings of the twigs with CO₂ for prolonged periods of time. The expected concentrations of CO₂, at the boundary layer between the atmosphere and the surfaces of the twigs, are over 1 000 ppm. As net photosynthesis of T. aphylla reaches maximal rates only at CO₂ concentrations of above 500 ppm, the plants may benefit from this extra source of carbon and may exploit it for maximal assimilation during the early morning hours. Thus, the "salt glands'of Tamarix , which are liable for the production of the alkaline recretum, may serve a triple purpose: (a) removal of excess salts out of the twigs, (b) provision of a cover of hygroscopic solutes that moistens the twigs and shortens the duration of transpiration, and (c) providing the plants with an environment enriched in CO₂.     

Striking convergence in the mouthpart evolution of stream-living algae grazers

This scanning-electron microscopic study demonstrates the convergent evolution of the mouthparts of various herbivorous stream animals (insects from different orders, an isopod, snails, fish, and a tadpole) feeding on epilithic algal pastures. This food source is rich but is often difficult to harvest. Nevertheless, a large number of species can live on it because they have evolved highly specialized mouthparts. There are four functional problems that an algae grazer has to solve: the algae must be removed from the stone, they have to be collected and crushed, and a current shield is needed to prevent the water flow sweeping away the food. Among the 30 algae grazers examined in this study, a limited number of morphological solutions have been found for each of these adaptational problems. There are multiple evolutionary pathways for mouthpart adaptation and even closely related species have often evolved different types of tools for the same function. This refects the existence of a certain amount of evolutionary scope. Such freedom of evolution is present, however, only at the beginning of the adaptiogenesis of an algae grazer. Once one of the evolutionary pathways is taken, further improvement of the mouthparts is possible only by the refinement of the ‘chosen’ type of tools. The consequence of this is that a large number of astonishing convergences have occurred in algae grazers that have independently trodden the same evolutionary pathway.     

Are the carbon costs of seed production related to the quantitative and qualitative performance? An appraisal for legumes and other crops

In the past great efforts have been made to gain a thorough understanding of the processes involved in carbon fixation but the fate of the acquired carbon has been somewhat neglected, although this aspect is crucial for improving yield performance without diminishing the quality of the harvested organs. To contribute to the crucial debate on that topic the aim of the present study was to propose some unbiased components concerning in particular grain legumes: ‘Is there any antagonism between high yield and increased nutritional quality, with a focus on protein content?’ An original approach has been used to study the impact of the modification of seed composition on the crop production, which combines theoretical calculations of energetic cost and field yield data. When applied to a wide range of species with varying seed composition, a plurispecific negative relationship between the theoretical carbon costs of seed production and the observed yields was demonstrated. The high-throughput of genetic markers could result in large-scale screening of seed quality parameters and such studies, while evaluating the impact of seed composition on crop yield, could also be used to provide data to forecast the economic impact of a new line with an original composition compared with its economically enhanced value.     

Influence of cadmium on the distribution of the essential trace elements zinc and copper in the liver and kidneys of rats

Cd induced changes of Zn and Cd distribution in the liver and kidneys were studied in relation to Cd metallothionein (MT) synthesis. Wistar male rats were given CdCl₂ by sc injection of .8, 1.5, and 3.0 mg Cd/kg three times a week for three weeks. Cd levels of liver and kidneys increased with the increment of Cd dosage and 80–90% of Cd was found in the cytosol. The MT fractions contained 80–89% cytosolic Cd in the liver and 55–75% Cd in the kidneys. Zn concentrations in the liver increased following Cd administration, But Zn in the kidneys showed only slight increase. There was a distinct decrease of Cu concentration in the liver of the 3.0 mg group. In contrast, Cu concentrations in the kidneys increased about three times in the .8 and 1.5 mg Cd groups, but Cu in the 3.0 mg group showed only 1.5 times increase. The changes of these metal concentrations were observed mainly in the cytosol. Non-MT-Cd in the kidneys was maximum in the 1.5 mg group, but the 3.0 mg group showed significant decrease. In parallel with this decrease of Cd, Cu and Zn in the kidneys showed similar decrease. When the kidneys are injured, Zn and Cu appear to leak from this organ.     

Contribution of solvent drag through intercellular junctions to absorption of nutrients by the small intestine of the rat

Summary The lumen of the small intestine in anesthetized rats was recirculated with 50 ml perfusion fluid containing normal salts, 25mm glucose and low concentrations of hydrophilic solutes ranging in size from creatinine (mol wt 113) to Inulin (mol wt 5500). Ferrocyanide, a nontoxic, quadrupally charged anion was not absorbed; it could therefore be used as an osmotically active solute with reflection coefficient of 1.0 to adjust rates of fluid absorption,J _v , and to measure the coefficient of osmotic flow,L _p . The clearances from the perfusion fluid of all other test solutes were approximately proportional toJ _v . FromL _p and rates of clearances as a function ofJ _v and molecular size we estimate (a) the fraction of fluid absorption which passes paracellularly (approx. 50%), (b) coefficients of solvent drag of various solutes within intercellular junctions, (c) the equivalent pore radius of intercellular junctions (50 Å) and their cross sectional area per unit path length (4.3 cm per cm length of intestine). Glucose absorption also varied as a function ofJ _v . From this relationship and the clearances of inert markers we calculate the rate of active transport of glucose, the amount of glucose carried paracellularly by solvent drag or back-diffusion at any givenJ _v and luminal glucose concentration and the concentration of glucose in the absorbate. The results indicate that solvent drag through paracellular channels is the principal route for intestinal transport of glucose or amino acids at physiological rates of fluid absorption and concentration. In the absence of luminal glucose the rate of fluid absorption and the clearances of all inert hydrophilic solutes were greatly reduced. It is proposed that Na-coupled transport of organic solutes from lumen to intercellular spaces provides the principal osmotic force for fluid absorption and triggers widening of intercellular junctions, thus promoting bulk absorption of nutrients by solvent drag. Further evidence for regulation of channel width is provided in accompanying papers on changes in electrical impedance and ultrastructure of junctions during Na-coupled solute transport.     

Responses of wild plants to nitrate availability

Summary Two annual species of Bromus, an invader (B. hordeaceus, ex B. mollis) and a non-invader (B. intermedius), were grown for 28 days in growth chambers, at 5 and 100 M NO ₃ ^- in flowing nutrient solution. No differences between the two species were observed at either NO ₃ ^- level, in terms of relative growth rate (RGR) or its components, dry matter partitioning, specific NO ₃ ^- absorption rate, nitrogen concentration, and other characteristics of NO ₃ ^- uptake and photosynthesis. The effects of decreasing NO ₃ ^- concentration in the solution were mainly to decrease the NO ₃ ^- concentration in the plants through decreased absorption rate, and to decrease the leaf area ratio through increased specific leaf mass and decreased leaf mass ratio. Organic nitrogen concentration varied little between the two treatments, which may be the reason why photosynthetic rates were not altered. Consequently, RGR was only slightly decreased in the 5-M treatment compared to the 100-M treatment. This is in contrast with other species, where growth is reduced at much higher NO ₃ ^- concentrations. These discrepancies may be related to differences in RGR, since a log-linear relationship was found between RGR and the NO ₃ ^- concentration at which growth is first reduced. In addition, a strong linear relationship was found between the RGR of these species and their maximum absorption rate for nitrate, suggesting that the growth of species with low maximum RGR may be partly regulated by nutrient uptake.     

Exogenous inorganic carbon sources for photosynthesis in seawater by members of the Fucales and the Laminariales (Phaeophyta): ecological and taxonomic implications

Summary Characteristics of inorganic carbon assimilation by photosynthesis in seawater were investigated in six species of the Fucales (five Fucaceae, one Cystoseiraceae) and four species of the Laminariales (three Laminariaceae, one Alariaceae) from Arbroath, Scotland. All of the algae tested could photosynthesise faster at high external pH values than the uncatalysed conversion of HCO ₃ ^- to CO₂ can occur, i.e. can use external HCO ₃ ^- . They all had detectable extracellular carbonic anhydrase activity, suggesting that HCO ₃ ^- use could involve catalysis of external CO₂ production, a view supported to some extent by experiments with an inhibitor of carbonic anhydrase. All of the algae tested had CO₂ compensation concentrations at pH 8 which were lower than would be expected from diffusive entry of CO₂ supplying RUBISCO as the initial carboxylase, consistent with the operation of energized entry of HCO ₃ ^- and / or CO₂ acting as a CO₂ concentrating mechanism. Quantitative differences among the algae examined were noted with respect to characteristics of inorganic C assimilation. The most obvious distinction was between the eulittoral Fucaceae, which are emersed for part of, or most of, the tidal cycle, and the other three families (Cystoseiraceae, Laminariaceae, Alariaceae) whose representatives are essentially continually submersed. The Fucaceae examined are able to photosynthesise at high pH values, and have lower CO₂ compensation concentrations, and lower K_1/2 values for inorganic C use in photosynthesis, at pH 8, than the other algae tested. Furthermore, the Fucaceae are essentially saturated with inorganic C for photosynthesis at the normal seawater concentration at pH 8 and 10°C. These characteristics are consistent with the dominant role of a CO₂ concentrating mechanism in CO₂ acquisition by these plants. Other species tested have characteristcs which suggest a less effective HCO ₃ ^- use and CO₂ concentrating mechanism, with the Laminariaceae being the least effective; unlike the Fucaceae, photosynthesis by these algae is not saturated with inorganic C in normal seawater. Taxonomic and ecological implications of these results are considered in relation to related data in the literature.     

Luxury consumption and specific utilization rates of three macroelements in two Taraxacum microspecies of contrasting mineral ecology

Plants of Taraxacum sellandii Dahlst., a microspecies adapted to fertile, and Taraxacum nordstedtii Dahlst., adapted to infertile soils, were cultured hydroponically, either on a complete nutrient solution or on one deprived of nitrogen, phosphorus, or potassium ions. For all four treatments, the growth and internal mineral concentration of the plants was monitored. For plants cultured on a complete nutrient solution, the uptake rates of nitrate, phosphate, and potassium ions were determined. Luxury consumption of the three macronutrients was computed as the excess of ion absorption over the ion uptake rates minimally required to sustain maximum growth. In these calculations the critical N, P, or K⁺ concentrations, earlier derived, were used as parameters describing the mineral status minimally required to allow maximum growth. Efficiency in use of the three macroelements at various levels of mineral accumulation was also computed. Finally, the response to phosphate starvation as related to phosphate uptake capacity and the accumulation of P was investigated.
The physiological properies investigated provide a causal background for the superior adaptation of T. nordstedtii as compared to T. sellandii to infertile sites. Taraxacum nordstedtii had a higher relative luxury consumption of NO₃^–, H₂PO^-₄, and K⁺, a higher efficiency in N and P use at N– and (severe) P-deficiency, respectively; and, after phosphate starvation, a relatively high preservation of phosphate uptake capacity and an enlargement of P storage. In combination with the low potential growth, luxury consumption will be particularly effective in T. nordstedtii in preventing or minimizing mineral deficiency. The distribution of minerals between cytoplasm and vacuoles as a factor in mineral use efficiency is discussed.