System-level adjustments to elevated CO2 in model spruce ecosystems

Atmospheric carbon dioxide enrichment and increasing nitrogen deposition are often predicted to increase forest productivity based on currently available data for isolated forest tree seedlings or their leaves. However, it is highly uncertain whether such seedling responses will scale to the stand level. Therefore, we studied the effects of increasing CO₂ (280, 420 and 560 μL L^-1) and increasing rates of wet N deposition (0, 30 and 90 kg ha^-1 y^-1) on whole stands of 4-year-old spruce trees (Picea abies). One tree from each of six clones, together with two herbaceous understory species, were established in each of nine 0.7 m² model ecosystems in nutrient poor forest soil and grown in a simulated montane climate for two years. Shoot level light-saturated net photosynthesis measured at growth CO₂ concentrations increased with increasing CO₂, as well as with increasing N deposition. However, predawn shoot respiration was unaffected by treatments. When measured at a common CO₂ concentration of 420 μL L^-1 37% down-regulation of photosynthesis was observed in plants grown at 560 μL CO₂ L^-1. Length growth of shoots and stem diameter were not affected by CO₂ or N deposition. Bud burst was delayed, leaf area index (LAI) was lower, needle litter fall increased and soil CO₂ efflux increased with increasing CO₂. N deposition had no effect on these traits. At the ecosystem level the rate of net CO₂ exchange was not significantly different between CO₂ and N treatments. Most of the responses to CO₂ studied here were nonlinear with the most significant differences between 280 and 420 μL CO₂ L^-1 and relatively small changes between 420 and 560 μL CO₂ L^-1. Our results suggest that the lack of above-ground growth responses to elevated CO₂ is due to the combined effects of physiological down-regulation of photosynthesis at the leaf level, allometric adjustment at the canopy level (reduced LAI), and increasing strength of below-ground carbon sinks. The non-linearity of treatment effects further suggests that major responses of coniferous forests to atmospheric CO₂ enrichment might already be under way and that future responses may be comparatively smaller.     

Multiple xenobiotic-inducible P450s are involved in alkoxycoumarin and alkoxyresorufin metabolism in higher plants

O-Dealkylation of two series of fluorescent 7-alkoxy-coumarins and 7-alkoxyphenoxazones by plant cytochrome P450s was investigated in Helianthus tuberosus tuber tissues treated with prototype P450 inducers, environmental pollutants or agrochemicals. Methoxy-, ethoxy-, propoxy-and butoxycoumarins and methoxy- and ethoxyresorufins were metabolized by fplant microsomes. Dealkylation of pentoxy- and benzyloxyresorufins was not detected. All dealkylating activities were enhanced by aging plant tissues in the presence of xenobiotics, in some cases up to 20-fold relative to the activities detected in control tissues. Increases in total P450 in the same tissues never exceeded 3-fold. The isozymes induced by prototype P450 inducers clearly differed from those in mammalian liver. That multiple P450s with overlapping substrate specificities were involved in the metabolism of both alkoxycoumarins and alkoxyresorufins was demonstrated by (1) the differential induction of the activities in response to exposure to xenobiotics, (2) the differential inhibition of the activities by clotrimazole, paclobutrazole and tetcyclacis in aminopyrine and benzo(a)pyrene-treated tissues, and(3) the selective inhibition observed with antibodies raised against purified ethoxycoumarin deethylase fractions. Our results suggest that the measurement of the dealkylation of such fluorescent substrates in plants might be useful to monitor environmental pollution.     

Variation in heat shock proteins within tropical and desert species of poeciliid fishes

The 70-kilodalton heat shock protein (hsp70) family of molecular chaperones, which contains both stress-inducible and normally abundant constitutive members, is highly conserved across distantly related taxa. Analysis of this protein family in individuals from an outbred population of tropical topminnows, Poeciliopsis gracilis, showed that while constitutive hsp70 family members showed no variation in protein isoforms, inducibly synthesized hsp70 was polymorphic. Several species of Poeciliopsis adapted to desert environments exhibited lower levels of inducible hsp70 polymorphism than the tropical species, but constitutive forms were identical to those in P. gracilis, as they were in the confamilial species Gambusia affinis. These differences suggest that inducible and constitutive members of this family are under different evolutionary constraints and may indicate differences in their function within the cell. Also, northern desert species of Poeciliopsis synthesize a subset of the inducible hsp70 isoforms seen in tropical species. This distribution supports the theory that ancestral tropical fish migrated northward and colonized desert streams; the subsequent decrease in variation of inducible hsp70 may have been due to genetic drift or a consequence of adaptation to the desert environment. Higher levels of variability were found when the 30- kilodalton heat shock protein (hsp30) family was analyzed within different strains of two desert species of Poeciliopsis and also in wild-caught individuals of Gambusia affinis. In both cases the distribution of hsp30 isoform diversity was similar to that seen previously with allozyme polymorphisms.      

RESEARCH OF SELECTIVE TESTS FOR DISCERNING "AN EFFICIENT ASSESSOR" IN TEXTURE PROFILING

To find selective and predictive tests in texture profiling, a series of 20 tests and 2 texture profiles were submitted to 25 subjects. Selection was carried out according to ranking, scoring and a texture property knowledge questionnaire. Two profiles were then done on 5 Bolognese sauce and 8 rice samples. Assessors were assessed by Spearman correlation coefficients for ranking tests, F values for scoring, average square canonical correlation coefficients for measuring the dimensionality of individual sample space, product discrimination and response repeatability for both Bolognese sauce and rice samples.
Characterization test results showed that subject ability varied widely according to the test and the profile. Only one significant relationship between the texture property knowledge test and rice profile performances was found. More tests were successfully related to one or several texture attributes of both profiles. The ability to complete a complex profile could be discerned, albeit with difficulty, through simple selection tests.     

Biotypes of Agrobacterium tumefaciens in Hungary

Isolates of Agrobacterium tumefaciens from Hungary were separated into three biotypes on the basis of their physiological characters. Biotypes 1 and 2 corresponded with those of Keane et al . (1970). The most common isolates were of biotype 2. Isolates from grapevines formed a separate biotype which might be distinguished from biotype 1 by D-(–)tartrate and malonate utilization. Many isolates with biotype-intermediate characters were found. Isolates utilizing D-(–)tartrate, erythritol and malonate were included into biotype 2, although many of them were 3–ketolactose positive. Biotypes were not separated geographically and biotype 1 and 2 apparently occurred together.     

Accumulation and metabolism of aldicarb by the free-living nematodes Aphelenchus avenae and Panagrellus redivivus

The accumulation and metabolism of aldicarb has been compared in two species of free-living soil nematodes, Aphelenchus avenae and Panagrellus redivivus, which differ considerably in their sensitivity to this and other pesticides. Similar levels of aldicarb were found to accumulate in the two species. The results showed that although the rate of uptake of aldicarb was greater in P. redivivus, so also was the rate of metabolism and elimination. Levels of toxic metabolites of aldicarb were two to three times higher in the more susceptible species A. avenae after 24 h incubation than in the less susceptible P. redivivus. The toxicological significance of these findings is discussed in relation to previous work with the organophosphorus pesticide phorate and its effects on the same two nematode species.     

A systematic approach to the simulation of short-term processes in the plant-environment complex

Abstract. A conceptual framework is presented for modelling short-term processes in the plant and its environment as an integrated system. Flows of water, water vapour, heat, momentum, CO₂, soluble carbohydrate and phosphorus are all described by equations of the same general type, i.e. in terms of diffusivity-type parameters, capacities and potential gradients. A representative volume of the crop is divided horizontally into layers and vertically between crop and environment for treatment by a finite-difference method. Vertical flow occurs in the atmosphere, soil, stems and larger roots, andilateral flow between leaves and air, and between finer roots and soil. The interception of direct sunlight and the flux densities of downward and upward diffuse radiation within layers are calculated by a step-wise procedure.
The conversions of materials within the plant are treated as functions of appropriate state variables. Schemes for carbon and phosphorus provide for flow to and from the translocation system, and for photosynthesis, respiration and growth.
A model of a fully-established lucerne crop is described and the sensitivity of model performance to changes in a number of parameter values explored. Simulation runs under varying conditions indicate realistic prediction of diurnal trends.     

Differentiation of New Metastatic Variants of B16 Melanoma Under Different Culture Conditions

The purpose of this study was to examine the differentiation of variant tumors of the B16 metastatic melanoma when tumors were grown serially under different culture conditions and transplanted into C57BL/6J black mice, lethal yellow A^y/a, albino c/c, and C⁺/c mutant mice. Morphological and biochemical markers of melanogenesis were examined in cells in culture and in the corresponding tumors. Cellular pigmentation was assessed in terms of the levels of DOPA and 5-S-CD and in terms of tyrosinase activity in the various cell lines and tumors. The observed change from high to low metastatic capacity, which was dependent on culture conditions, appeared to be unrelated to melanogenesis even though changes were observed in the biochemical melanotic phenotype. Overall, tumor cells from spontaneous pulmonary metastases appear to differentiate in ways that are unrelated to the instability of experimental metastatic capacity. The melanotic phenotype in albino c/c and C⁺/c mice was dependent on the phenotype of the parental tumors. A marked difference was observed between two pigmentation compartments, one of which was stable in the B16 control, while the other was unstable in YB16 and MB16 variant cells and in the tumors derived from them. It appears, therefore, that the metastatic capacity of B16 metastatic variants is changeable and is independent of the unstable melanogenic behavior. The production of metastases and the differentiation of tumors in the present experiments appeared to be related to the genetic background of the mice and the epigenetic metabolic environment of tumors and cells.