Retention time as a primary determinant of colour and light attenuation in two tropical Australian reservoirs

1. The light climates of Darwin River Reservoir (DRR) and Manton River Reservoir (MRR), in northern Australia, are compared for an 8-year period. The reservoirs are subject to the same wet/dry tropical climate and have similar catchment characteristics, but differ in their basin morphology, retention time and trophic status.
2. Median euphotic depths in DRR and MRR were 9.7 and 4.4 m, respectively. Seasonal variation in each reservoir's euphotic depth was best explained by colour, based on a stepwise linear regression. Turbidity was excluded from the two regressions, while chlorophyll a concentration was significant only for the MRR regression.
3. Both reservoirs showed the same seasonal pattern for colour. Wet season inflow increased reservoir colour, and was followed by a reduction in colour due to photodegradation and microbial decomposition of humic material, reaching a minimum before the next wet seasons inflow.
4. Although the colour of catchment run-off into both reservoirs was similar, MRR colour was two to three times greater than that measured in DRR. The higher colour and greater light attenuation of MRR is attributed primarily to its shorter retention time, and therefore shorter time for colour removal. Annual retention time accounted for 97% of the variability of average annual colour (measured as absorption at 440 nm), based on a linear regression of log₁₀ transformed data for both reservoirs.
5. Long retention times favour reduced colour, increasing water transparency, particularly in water bodies of low trophic state and inorganic turbidity.     

Evidence for Reversible Tyrosine Protein Phosphorylation in the Okadaic Acid-Producing Marine Dinoflagellate Prorocentrum lima

ABSTRACT. The protist Prorocentrum lima , a primary producer of the tumour promoter okadaic acid, is a member of the dinoflagellate class of marine microorganisms. Herein, we have identified and characterized a protein tyrosine kinase (designated PLIK 1A) in P. lima that autophosphorylates almost exclusively on tyrosine residues. PLIK 1A was shown to have an approximate molecular mass of 38 kDa by SDS-PAGE and a native molecular mass within the range of 47–55 kDa by Superdex-75 gel filtration. Phosphoamino acid analysis of autophosphorylated PLIK 1A revealed the presence of phosphotyrosine and autophosphorylated PLJK 1A reacted with monoclonal anti-phosphotyrosine antibodies in a Western immunoblot. In addition, two protein tyrosine phosphatases were identified in P. lima that had apparent molecular masses within the ranges of 150–168 kDa and 73–82 kDa as determined by Superdex-200 gel filtration. These P. lima phosphatases, termed PLPTP-I and PLPTP-II, efficiently dephosphorylated tyrosine phosphorylated myelin basic protein. owever, only PLPTP-I was capable of dephosphorylating the tyrosine phosphorylated substrate angiotensin. Both PLPTP-I and PLPTP-II were able to dephosphorylate tyrosine autophosphorylated PLIK 1A. These data provide the first evidence for reversible tyrosine protein phosphorylation in P. lima by protein tyrosine kinases and phosphatases     

Biochemical regulation of isoprene emission

Isoprene (C₅H₈) is emitted from many plants and has a substantial effect on atmospheric chemistry. There are several models to estimate the rate of isoprene emission used to calculate the impact of isoprene on atmospheric processes. The rate of isoprene synthesis will depend either on the activity of isoprene synthase or the availability of its substrate dimethylallyl pyrophosphate (DMAPP). To investigate long‐term regulation of isoprene synthesis, the isoprene emission rate of 15 kudzu leaves was measured. The chloroplast DMAPP level of the five leaves with the highest emission rates and the five leaves with the lowest rates were determined by non‐aqueous fractionation of the bulked leaf samples. Leaves with high basal emission rates had low levels of DMAPP whereas leaves with low basal emission rates had high DMAPP levels in their chloroplasts indicating that the activity of isoprene synthase exerts primary control over the basal emission rate. To investigate short‐term regulation, isoprene precursors were fed to leaves. Feeding dideuterated deoxyxylulose (DOX‐d₂) to Eucalyptus leaves resulted in the emission of dideuterated isoprene. Results from DOX‐d₂ feeding experiments indicated that control of isoprene emission rate was shared between reactions upstream and downstream of the DOX entry into isoprene metabolism. In CO₂‐free air DOX always increased isoprene emission indicating that carbon availability was an important control factor. In N₂, isoprene emission stopped and could not be recovered by adding DOX‐d₂. Taken together, these results indicate that the regulation of isoprene emission is shared among several steps and the relative importance of the different steps in controlling isoprene emission varies with conditions.     

Retention time as a primary determinant of colour and light attenuation in two tropical Australian reservoirs

1. The light climates of Darwin River Reservoir (DRR) and Manton River Reservoir (MRR), in northern Australia, are compared for an 8-year period. The reservoirs are subject to the same wet/dry tropical climate and have similar catchment characteristics, but differ in their basin morphology, retention time and trophic status.
2. Median euphotic depths in DRR and MRR were 9.7 and 4.4 m, respectively. Seasonal variation in each reservoir's euphotic depth was best explained by colour, based on a stepwise linear regression. Turbidity was excluded from the two regressions, while chlorophyll a concentration was significant only for the MRR regression.
3. Both reservoirs showed the same seasonal pattern for colour. Wet season inflow increased reservoir colour, and was followed by a reduction in colour due to photodegradation and microbial decomposition of humic material, reaching a minimum before the next wet seasons inflow.
4. Although the colour of catchment run-off into both reservoirs was similar, MRR colour was two to three times greater than that measured in DRR. The higher colour and greater light attenuation of MRR is attributed primarily to its shorter retention time, and therefore shorter time for colour removal. Annual retention time accounted for 97% of the variability of average annual colour (measured as absorption at 440 nm), based on a linear regression of log₁₀ transformed data for both reservoirs.
5. Long retention times favour reduced colour, increasing water transparency, particularly in water bodies of low trophic state and inorganic turbidity.     

Effects of Mitochondrial Inhibitors on Intraerythrocytic Plasmodium falciparum in In Vitro Cultures1

ABSTRACT. Malarial parasites infecting mammalian hosts are considered to be homolactate fermentors at their asexual intraerythrocytic developmental stage; however, existing ultrastructural and biochemical evidence suggest that their acristate mitochondria could be involved in energy metabolism. In the present study, inhibitors of mitochondrial function including compounds which act on NADH and succinate dehydrogenases, electron transport and mitochondrial ATPase, as well as uncouplers, were found to inhibit the growth and propagation of the human parasite Plasmodium falciparum in in vitro cultures at concentrations that specifically affect mitochondrial functions. Direct measurement of parasite protein and nucleic acid synthesis in synchronized cultures showed that throughout the parasite life cycle both processes were inhibited, the latter process being more sensitive. These results strongly suggest that intraerythrocytic malarial parasites require mitochondrial energy production.