Components of relative growth rate and sensitivity to nitrogen availability in annual and perennial species of Bromus

Summary Two grass species, the annual Bromus sterilis and the perennial Bromus erectus, were grown from seeds for 28 days in a hydroponic culture system at 1 and 100 M NO₃ ^- in the nutrient solution. At 100 M NO₃ ^-, the relative growth rate (RGR) of the perennial was 30% lower than that of the annual. This was only the consequence of the higher specific mass of its leaves, since its leaf mass ratio was higher than that of the annual and the unit leaf rates (ULR), calculated on an area basis, were similar for the two species. At 1 M, the RGR of the annual was 50% lower than at 100 M, while that of the perennial was not significantly lower. This was due mainly to a lower ULR for the annual. while for the perennial ULR was the same in both treatments. These differences between the two species were all the more striking in that the differences in total nitrogen concentrations and nitrate reductase activities between the two treatments were very similar for both species. These different responses together with differences in the nitrogen productivity of the two species suggest that the level of nutrient availability may play an important role in the distribution of these Bromus species in natural habitats. Scope: Components of growth and response to nitrate availability in annual and perennial grasses     

Immunoquantification and enzyme kinetics of alpha-L-iduronidase in cultured fibroblasts from normal controls and mucopolysaccharidosis type I patients.

alpha-L-Iduronidase activity is deficient in mucopolysaccharidosis type I (MPS I; Hurler syndrome, Scheie syndrome) patients and results in the disruption of the sequential degradation of the glycosaminoglycans dermatan sulfate and heparan sulfate. A monoclonal antibody-based immunoquantification assay has been developed for alpha-L-iduronidase, which enables the detection of at least 16 pg alpha-L-iduronidase protein. Cultured human skin fibroblasts from 12 normal controls contained 17-54 ng alpha-L-iduronidase protein/mg extracted cell protein. Fibroblasts from 23 MPS I patients were assayed for alpha-L-iduronidase protein content. Fibroblast extracts from one MPS I patient contained at least six times the level of alpha-L-iduronidase protein for normal controls--but contained no associated enzyme activity--and is proposed to represent a mutation affecting the active site of the enzyme. Fibroblast extracts from 11 MPS I patients contained 0.05-2.03 ng alpha-L-iduronidase protein/mg extracted cell protein, whereas immunodetectable protein could not be detected in the other 11 patients. Four fibroblast extracts with no immunodetectable alpha-L-iduronidase protein had residual alpha-L-iduronidase activity, suggesting that the mutant alpha-L-iduronidase in cultured cells from these MPS I patients has been modified to mask or remove the epitopes detected by two monoclonal antibodies used in the quantification assay. Both the absence of immunoreactivity in a mild MPS I patient and high protein level in a severe MPS I patient present limitations to the use of immunoquantification analysis as a sole measure of patient phenotype. Enzyme kinetic analysis of alpha-L-iduronidase from MPS I fibroblasts revealed a number of patients with either abnormal substrate binding or catalytic activity.(ABSTRACT TRUNCATED AT 250 WORDS)     

Cooperative Action of Rhizobium meliloti Nodulation and Infection Mutants during the Process of Forming Mixed Infected Alfalfa Nodules

Alfalfa plants co-inoculated with Rhizobium meliloti nodulation (Nod-) and infection mutants deficient in exopolysaccharide production (Inf-EPS-) formed mixed infected nodules that were capable of fixing atmospheric nitrogen. The formation of infected nodules was dependent on close contact between the inoculation partners. When the partners were separated by a filter, empty Fix- nodules were formed, suggesting that infection thread formation in alfalfa is dependent on signals from the nodulation and infection genes. In mixed infected nodules, both nodulation and infection mutants colonized the plant cells and differentiated into bacteroids. The formation of bacteroids was not dependent on cell-to-cell contact between the mutants. Immunogold/silver staining revealed that the ratio of the two mutants varied considerably in colonized plant cells following mixed inoculation. The introduction of an additional nif/fix mutation into one of the inoculation partners did not abolish nitrogen fixation in mixed infected nodules. The expression of nif D::lacZ fusions additionally demonstrated that mutations in the nodulation and infection genes did not prevent the nif genes from being expressed in the mutant bacteroids.     

Water relations and leaf chemistry of Chrysothamnus nauseosus ssp. consimilis (Asteraceae) and Sarcobatus vermiculatus (Chenopodiaceae)

At Mono Lake, California, we investigated field water relations, leaf and xylem chemistry, and gas exchange for two shrub species that commonly co-occur on marginally saline soils, and have similar life histories and rooting patterns. Both species had highest root length densities close to the surface and have large tap roots that probably reach ground water at 3.4-5.0 m on the study site. The species differed greatly in leaf water relations and leaf chemistry. Sarcobatus vermiculatus had a seasonal minimum predawn xylem pressure potential (ψ_pd) of -2.7 MPa and a midday potential (ψ_md) of -4.1 MPa. These were significantly lower than for Chrysothamnus nauseosus, which had a minimum ψ_pd of -1.0 MPa and ψ_md of -2.2 MPa. Sarcobatus had leaf Na of up to 9.1 % and K up to 2.7 % of dry mass, and these were significantly higher than for Chrysothamnus which had seasonal maxima of 0.4% leaf Na and 2.4 % leaf K. The molar ratios of leaf K/Na, Ca/Na, and Mg/Na were substantially lower for Sarcobatus than for Chrysothamnus. Xylem ionic contents indicated that both species excluded some Na at the root, but that Chrysothamnus was excluding much more than Sarcobatus. The higher Na content of Sarcobatus leaves was associated with greater leaf succulence, lower calculated osmotic potential, and lower xylem pressure potentials. Despite large differences in water relations and leaf chemistry, these species maintained similar diurnal patterns and rates of photosynthesis and stomatal conductance to water vapor diffusion. Sarcobatus ψ_pd may not reflect soil moisture availability due to root osmotic and hydraulic properties.     

Measurement of Growth at Very Low Rates ((mu) >= 0), an Approach To Study the Energy Requirement for the Survival of Alcaligenes eutrophus JMP 134

Alcaligenes eutrophus JMP 134 was grown in a recycling-mode fermenter with 100% biomass retention on 2,4-dichlorophenoxyacetic acid (2,4-D), phenol, and fructose. The growth pattern obtained given a constant supply of substrates exhibited three phases of linear growth on all three substrates. The transition from phase 1 to phase 2, considered to correspond to the onset of stringent (growth) control as indicated by a significant increase in guanosine 5(prm1)-bisphosphate 3(prm1)-bisphosphate (ppGpp), took place at 0.016 h(sup-1) with 2,4-D and at about 0.02 h(sup-1) with phenol and fructose. In the final phase, phase 4, which was achieved after the growth rate on the respective substrates fell below 0.003 to 0.001 h(sup-1), a constant level of biomass was obtained irrespective of further feeding of substrate at the same rate. The yield coefficients decreased by 70 to 80% from phase 1 to phase 3 and were 0 in phase 4. The stationary substrate concentrations s(infmin) in phase 4, calculated from the kinetic constants of the strain, were 1.23, 0.34, and 0.23 (mu)M for 2,4-D, phenol, and fructose, respectively. These figures characterize the minimum stationary substrate concentrations required in a dynamic system to keep A. eutrophus alive. This is caused by a substrate flux which enables growth at a rate >=0 due to the provision of energy to an extent at least satisfying maintenance requirements. According to the constant feed rates of the substrates and the final and stable biomass concentrations, this maintenance energy amounts to 14.4, 4.0, and 2.4 (mu)mol of ATP (middot) mg of dry mass(sup-1) h(sup-1) for 2,4-D, phenol, and fructose, respectively, after correction for the fraction of living cells. The increased energy expenditure in the case of 2,4-D is discussed with respect to uncoupling.     

Anonymous nuclear DNA markers in the American oyster and their implications for the heterozygote deficiency phenomenon in marine bivalves

A puzzling population-genetic phenomenon widely reported in allozyme surveys of marine bivalves is the occurrence of heterozygote deficits relative to Hardy-Weinberg expectations. Possible explanations for this pattern are categorized with respect to whether the effects should be confined to protein-level assays or are genomically pervasive and expected to be registered in both protein- and DNA-level assays. Anonymous nuclear DNA markers from the American oyster were employed to reexamine the phenomenon. In assays based on the polymerase chain reaction (PCR), two DNA-level processes were encountered that can lead to artifactual genotypic scorings: (a) differential amplification of alleles at a target locus and (b) amplification from multiple paralogous loci. We describe symptoms of these complications and prescribe methods that should generally help to ameliorate them. When artifactual scorings at two anonymous DNA loci in the American oyster were corrected, Hardy-Weinberg deviations registered in preliminary population assays decreased to nonsignificant values. Implications of these findings for the heterozygote-deficit phenomenon in marine bivalves, and for the general development and use of PCR-based assays, are discussed.