Heterotrophic plant cell suspension cultures for monitoring biological activity in agrochemical research. Comparison with screens using algae,germinating seeds and whole plants

Heterotrophically cultured cell suspensions are used increasingly in agrochemical research for screening plant-growth retardants and herbicides which influence plant meristems. For this purpose, a large-scale microscreen has been devised, which permits the objective monitoring of cell division by measuring the conductivity in cell suspensions cultured in test tubes. Comparing the effects of a wide spectrum of growth retardants and herbicides with different primary modes of action, the test was most sensitive to nitrogen-geterocyclic retardants in wheat-cell suspensions and to sulfonylurea > imidazolinone > cyclohexanedione, oxy-phenoxypropionic acid, nitrile > glufosinate, phenoxy acid, bipyridylium and diphenyl ether herbicides in maize and oilseed rape cell cultures. As had been expected, inhibitors of photosynthetic processes were only slightly active. The results of the tests were compared with the effects of the compounds on germinating seeds of cress (Lepidium sativum L.) and on photoautotrophic systems using algal cell suspensions (Scenedesmus acutus) and duckweeds (Lemna paucicostata). It is suggested that heterotrophic cell suspensions, in combination with the series of biotests mentioned above, are a valuable complement to the whole-plant screens used routinely in industrial laboratories. They are particularly useful for identifying compounds whose biological activity is masked by limited penetration or translocation behaviour in whole plants.     

Modern forestry vehicles and their impact on soil physical properties

Mechanized harvesting procedures for typical forest vehicles were analysed to examine soil stresses and displacements occurring in soil profiles and to reveal changes in physical properties of forest soils. All field experiments were carried out under traffic lanes of standard forest vehicles in forest stands of the southern Black Forest. The soil stresses were determined using stress state transducers (SST) and displacement transducer systems (DTS) at depths of 20 and 40 cm. Complete harvesting and trunk-logging processes with a total time span of 9 min were observed. The maximum vertical stresses for all experiments exceeded 200 kPa; some experiments showed maximum vertical stresses up to 500 kPa or more at a depth of 20 cm. To evaluate the impact of soil stresses on soil structure, the internal soil strength was determined by predicting the precompression stress. Comparison of soil stress data with the natural bearing capacity of the natural forest soil proves that sustainable traffic is not possible, irrespective of the vehicle type and the working process. Topsoil and subsoil compaction, an increase in the precompression stresses, deep rutting and vertical as well as horizontal soil displacement associated with shearing effects took place and affected the mechanical strength and the physical properties of forest soils. Considering these results, heavy forest machinery has a severe impact on soil physical properties such as air, heat, water fluxes and rootability. In order to sustain the present undamaged soil condition, a change in harvest logistics and organisation is necessary. This can be achieved with a permanent skid-trail system which has already been designed to implement new guidelines in Baden-Württemberg, Germany (Ministerium für Ernährung und ländlichen Raum, Baden-Württemberg 2003, p 27).     

Tree Planting by Smallholder Farmers in the Upper Catchment of Lake Tana Watershed,Northwest Ethiopia

Tree growing by smallholder farmers is an emerging livelihood strategy in Lake Tana catchment. The objectives of this study were to (1) identify the most important tree species grown, (2) investigate the drivers of the existing pattern, and (3) identify determinants of the number and diversity of tree species and their spatial patterns. Survey data were collected from 200 households. Multiple linear regression was employed to identify the determinants of tree growing behaviour of households and spatial variables affecting the abundance of tree species. Eucalyptus globulus, Acacia decurrens and E. camaldulensis dominate woodlots. Only a fraction of the forest production is used by the households, the rest being sold as poles or charcoal. Location in relation to market centres, number of livestock owned, landholding size and age of household head were found to positively affected the number of tree species and trees grown. Gender affected the species and spatial pattern of trees. Woodlots, farm boundaries and homesteads were found to be important tree growing niches. These results substantiate the proposition that farmers assign their parcels of land to uses that increase the rent value of the land, and this value is affected by access to roads. Woodlots are on the increase at the cost of productive agricultural land. Provision of a tree planting extension service may increase participation of farmers in tree planting, and a management-oriented tree planting extension service may give desirable results.     

Xylem sap flow and drought stress of Fraxinus excelsior saplings

We report on diurnal and seasonal variations in sap flow rate and stem water potential of Fraxinus excelsior L. saplings growing at the edge of a Fraxino-Aceretum forest in western Germany. Because of shallow soil, the trees were subjected to drought in summer. When soil water availability was not limiting, sap flow rate was related to changes in solar radiation and vapor pressure deficit. Maximum transpiration rates per leaf area were 3.5-7.4 mmol m-2 s-1, and maximum daily totals were 1.7-3.3 kg m-2 day-1. Under drought conditions, stem water potential dropped to midday minima of -2.6 to -3.5 MPa and sap flow rate was strongly related to this parameter. After the drought period, reduced apparent (whole-plant) hydraulic conductance was observed, which was attributed to a continued reduction in stomatal conductance after the drought stress had ceased. A model was developed that linked sap flow rate directly to climatic variables and stem water potential. Good correlation between measured and simulated sap flow rates allowed the model to be used for data interpretation.     

Testing the unifying theory of ozone sensitivity with mature trees of Fagus sylvatica and Picea abies

The broad range in plant responses to chronic O(3) exposure compels a search for integrative, underlying principles. One such approach is the unifying theory proposed by Reich (1987), which combines the O(3) response of contrasting physiognomic classes of plants on the basis of their intrinsic leaf diffusive conductance and, hence, capacity for O(3) uptake. Physiognomic classes differ in the proportional decline in photosynthesis and growth when compared on the basis of cumulative O(3) exposure per unit time, but converge when compared on the basis of O(3) uptake per unit time or cumulative O(3) uptake over the entire lifetime of the leaf. The theory is based on observations on a large number of contrasting plant species, relying primarily on studies of juvenile trees subjected to short-term O(3) exposure. To test the applicability of the unifying theory to mature trees, broadleaf deciduous European beech (Fagus sylvatica L.) and the evergreen conifer Norway spruce (Picea abies (L.) Karst.) in a mature mixed stand were exposed to either ambient air (control) or air with twice the ambient O(3) concentration delivered into the canopy by means of a free-air fumigation system. We accounted for differences in growing season length, leaf longevity and O(3)-related effects on leaf diffusive conductance in determining total O(3) uptake over the lifetime of the leaf. On this basis, Norway spruce needles required 5 years to take up as much O(3) as did beech leaves in one growing season. The core of the unifying theory on O(3) sensitivity was substantiated in relation to O(3) exposure and uptake. However, contrary to the unifying theory, which was formulated on the basis of results with juvenile trees, the O(3) response of mature trees in a natural stand was more complex. The increased complexity was attributed to additional environmental stressors, stress compensation at the whole-tree level, and differential O(3) sensitivities of leaves according to age class and position within the canopy. Contrary to the theory, photosynthesis was no less sensitive to O(3) in Norway spruce than that of beech, and was reduced in the twice-ambient O(3) regime in the first year of exposure.     

Comparison of binding and effects of Escherichia coli Shiga toxin 1 on bovine and ovine granulocytes

Granulocytes play a pivotal role in the pathogenesis of Shiga toxin (Stx)-producing Escherichia coli (STEC) related diseases in humans. Granulocytes are attracted and activated by Stxs in the enteric mucosa and are believed to thereby contribute to the intestinal inflammation. Mature ruminants, the main reservoir hosts of STEC, do not develop pathological changes that can be attributed to the Stxs. To prove whether the latter phenomenon correlates with the inability of the Stxs to affect granulocytes of ruminants, we investigated the ability of Stx1 to bind to granulocytes of cattle and sheep and analysed the effects of Stx1 on viability, phagocytosis, and oxidative burst activity. Bovine granulocytes from blood and milk did not express Stx1-binding sites even after activation of the cells and also were resistant to Stx1. In contrast to bovine granulocytes, granulocytes of sheep constitutively expressed Stx1-receptors of the Gb(3)/CD77 type ex vivo and bound the recombinant B-subunit of Stx1 (rStxB1). Stx1 holotoxin induced apoptosis in ovine granulocytes after prolonged incubation (18h) but Stx1 only slightly altered the phagocytosis and oxidative burst activities. The rStxB1 had no effect on granulocytes of either species. While arguing in favour of our initial hypothesis, that granulocytes of both, cattle and sheep are not activated by Stxs, the results of our study are the first evidences for differences in the cellular distribution of Stx-receptors in species equally regarded as STEC carriers.