The application ofin vivo techniques in the study of metabolic aspects of ion absorption in crop plants

Summary Little is known about the biochemical basis of the genotypic differences in the capacity for ion absorption and transport shown by many crop species. If these differences reflect the abundance of a specific membrane component or the activity of an enzyme we need to have some indication of thein vivo operation of these systems in whole plants. Thein vivo assessment of glycolytic enzymes is illustrated by the effects of mannose on the transport of phosphate in maize varieties. The application of high resolution³¹P-NMR to the study of intermediary metabolismin vivo is also helpful in following transport capacity. The five-fold rise in respiratory rate that occurs when freshly cut potato slices are maintained in aerated water for 24 hours is accompained by the turning on of a wide range of biochemical systems. Major increases in the capacity for absorption of phosphate from low concentrations (0.1 μM–10 μM) and in the phosphorylative ability of the tissue are seen, indicating the synthesis of a carrier involved in phosphate transport. These capacities differ markedly between individual tissues of the tuber,i. e. pith, parenchyma, cortex and buds and large differences have been observed between comparable tissue from different varieties. Varieties grown under similar conditions have been compared and shown to exhibit different kinetics with respect to the development of the low concentration absorption site and in their sensitivity to the effects of uncouplers such as 2,4-dinitrophenol.     

Size selection of latex beads by blackfly larvae (Diptera: Simuliidae) in the laboratory

In laboratory experiments, blackfly larvae collected from a lake outlet, a woodland and a meadow stream were tested for size selection of latex beads of < Ito > 100 μm diameters. 3 suspensions of varying proportions for each size category were supplied to these blackfly larvae in common experiments. Comparisons between the size frequency distributions of particles supplied and the particle compositions in the larval guts showed intra- and interspecific differences and were quantified by calculating Jacobs' electivity index. In all species selection of larger particles increased with the larger larval instars. Although there was a positive selectivity of small particles in some cases, the ingested proportion of large particles increases volumes and biomasses of gut content and may be more important for larval growth than small particles.     

Dihydroquercetin accumulation in the medium of some wild carrot culture subclones

Approximately half of the subclones examined from one clone of the wild carrot cell culture WC63-1-9-1 accumulated dihydroquercetin in the culture medium. The amount of dihydroquercetin accumulated in the medium varied with the subclone used, the size of the inoculum, the medium used and the time of sampling.Dedicated to Dr. Friedrich Constabel on the occasion of his 60th birthday     

The particle size characteristics of fluvial suspended sediment: an overview

The particle size characteristics of suspended sediment are of fundamental importance in understanding its role in a variety of environmental processes. Existing knowledge concerning the spatial and temporal variability of the grain size composition of suspended sediment is, however, relatively limited. At the global scale, major contrasts may exist between individual rivers in the calibre of their suspended load and this may be related to a number of controls including climate, catchment geology and basin scale. Any attempt to understand the precise relationship between the grain size characteristics of suspended sediment and those of its source material must also take account of the selectivity of erosion and delivery processes. A local case study undertaken by the authors in the 1500 km² basin of the River Exe in Devon, UK is used to illustrate the considerable spatial variability that may occur within a relatively small area and the complexity of the associated controls.Available evidence concerning the temporal variability of the grain size characteristics of suspended sediment emphasises the diverse patterns of behaviour that may exist and the complexity of the controls involved. In some rivers the sediment may become coarser as flow increases, in others it may become finer, whilst in others it may exhibit a relatively constant grain size composition. Data from the local case study in the Exe basin are again used to highlight the considerable diversity in response to changing discharge that may occur within a relatively small area.Any attempt to understand the dynamics of sediment movement through a river system must also take account of the potential contrast between the ultimate and effective particle size distribution of suspended sediment in response to aggregation. Results from the Exe basin study indicate that even in rivers with relatively low solute concentrations, almost an order of magnitude difference may exist between the median particle size associated with the ultimate and effective grain size distributions.     

Relative importance of temporal and spatial heterogeneity in the zooplankton community of an artificial reservoir

Zooplankton samples were collected monthly at three stations in Ogochi Reservoir during 1980, and the temporal and horizontal variations in the density of dominant taxa were evaluated by a standard 2-way ANOVA with random effects. The analysis revealed that horizontal is greater than temporal variation in the warm water season (> 18 °C), whereas temporal variation is greater in the cold water season (< 18 °C). Horizontal heterogeneity of the zooplankton community found in the warm water season seems to be associated with differences in site-specific conditions.     

Microgeographic distribution of immature Ixodes dammini ticks correlated with that of deer

In order to determine whether the small-scale distribution of immature Ixodes dammini Spielman et al. corresponds closely to the activity patterns of white-tailed deer, Odocoileus virginianus (Zimmerman), these relationships were examined in a site on Long Island, New York, U.S.A. We first determined the extent and temporal pattern of adult ticks feeding on deer by examining twenty-three resident deer tranquilized during September-December 1985. I. dammini adults infested deer throughout this fall period, most abundantly during October and November. With radio-telemetry collars attached to deer we determined the relative frequency that they occupied 0.25 ha quadrats of the study site. During the following summer, we examined white-footed mice, Peromyscus leucopus (Rafinesque), that inhabited these quadrats and removed immature ticks from each. 8975 larval and 163 nymphal I. dammini were removed from 208 mice trapped in forty-three such quadrats. The frequency of deer using these quadrats was positively correlated with both the number of larval and of nymphal ticks per mouse. These results suggest that risk of I. damminiborne zoonotic disease may be decreased by locally reducing deer density in sites that experience intense human activity.     

Cultivar differences in the rate of nitrate uptake by intact wheat plants as related to growth rate

Six Argentinian wheat ( Triticum aestivum L.) cultivars grown in nutrient solutions in controlled environment were compared for their nitrate uptake rates on a root dry weight basis. Up to 3-fold differences were observed among the cultivars at 16, 20 and 24 days from germination, either when measured by depletion from the nutrient solution in short-term experiments, or by total N accumulation in the tissue during 8 days.
No differences in total N concentration in root or shoots were found among cultivars. Although the different cultivars showed significant differences in shoot/root ratio and nitrate reductase activity (EC 1.6.6.1) in the roots, none of these parameters was correlated with the nitrate uptake rate. However, nitrate uptake was found to be positively correlated (r = 0.99) with the shoot relative growth rate of the cultivars. The three cultivars with the highest nitrate uptake rates and relative growth rates showed a positive correlation between root nitrate concentration and uptake. However, this correlation was not found in the cultivars with the lowest growth and uptake rates.
Our results indicate that the difference in nitrate uptake rate among these cultivars may only be a consequence of their differences in growth rate, and it is suggested that at least two mechanisms regulate nitrate uptake, one working when plant demand is low and another when plant demand is high.     

Differences in learning by foraging juvenile pumpkinseed and bluegill sunfish in a structured habitat

Synopsis We investigated the ability of two congeneric species of sunfish to learn to forage on a novel prey item in feeding arenas containing structured habitats. Eight bluegill sunfish and eight pumpkinseed sunfish were given the opportunity to forage on whiteworms daily for 10 days. Each day, several behavioural measures were recorded for each fish. Both species of sunfish learned to feed over the 10-day period but the bluegill sunfish learned to feed more quickly than the pumpkinseed sunfish. Pumpkinseeds, however, attained a higher level of foraging efficiency. The differences in learning and foraging efficiency were related to body morphology.