How much water does a river need?

1. This paper introduces a new approach for setting streamflow-based river ecosystem management targets and this method is called the 'Range of Variability Approach' (RVA). The proposed approach derives from aquatic ecology theory concerning the critical role of hydrological variability, and associated characteristics of timing, frequency, duration, and rates of change, in sustaining aquatic ecosystems. The method is intended for application on rivers wherein the conservation of native aquatic biodiversity and protection of natural ecosystem functions are primary river management objectives.
2. The RVA uses as its starting point either measured or synthesized daily streamflow values from a period during which human perturbations to the hydrological regime were negligible. This streamflow record is then characterized using thirty-two different hydrological parameters, using methods defined in Richter et al . (1996). Using the RVA, a range of variation in each of the thirty-two parameters, e.g. the values at ± 1 standard deviation from the mean or the twenty-fifth to seventy-fifth percentile range, are selected as initial flow management targets.
3. The RVA targets are intended to guide the design of river management strategies (e.g. reservoir operations rules, catchment restoration) that will lead to attainment of these targets on an annual basis. The RVA will enable river managers to define and adopt readily interim management targets before conclusive, long-term ecosystem research results are available. The RVA targets and management strategies should be adaptively refined as suggested by research results and as needed to sustain native aquatic ecosystem biodiversity and integrity.     

DNA Biosynthesis in Chloroplasts: I. CHARACTERIZATION OF AND DEVELOPMENTAL VARIATION IN BOTH LIGHT- AND ATP-DRIVEN THYMIDINE INCORPORATION INTO DNA IN ISOLATED INTACT CHLOROPLASTS

Intact chloroplasts from young pea leaves were able to incorporate[³H]thymidine into DNA at relatively high rates (50 pmol mg^–1chlorophyll h^–1 or more), using light as the sole energysource. The intact plastids were also able to synthesize DNAin darkness, but only if ATP and MgCl₂ (MgATP) were both present.The rates of MgATP-driven assimilation in darkness were equalto or greater than light-driven activity. Neither light nordithiothreitol pretreatments enhanced thymidine incorporationin darkness, suggesting that enzymes of chloroplast DNA (ctDNA)biosynthesis are not regulated via a thioredoxin-type system.Although exogenous nucleosides (other than [³H]thymidine) werenot an absolute requirement, dramatically elevated rates ofincorporation (over 300 pmol mg^–1 chlorophyll h^–1)were seen when adenosine, cytidine, guanosine and thymidinewere supplied in combination (500 mmol m^–3 each). RadiolabelledDNA synthesized by the isolated chloroplasts was prepared usinga new heat extraction method. After digestion by restrictionendonucleases, ctDNA synthesized in organello was found to givetypical autoradiography patterns for chloroplast DNA. ExonucleaseIII studies suggested that 5% to 15% of the newly synthesizedDNA might be in a closed circular form. MgATP-driven synthesisin darkness was highly age-dependent. Chloroplasts from young(6 to 8-d-old) plants, or alternatively the youngest leavesof more mature plants, were 4–10 times more active thanthose from older tissues. Although these data do not establishconclusively that replication-type synthesis was occurring inthe isolated chloroplasts, they are consistent with this suggestion. Key words: Chloroplast DNA replication, isolated chloroplasts, chloroplast DNA synthesis     

Obtention d'épinastie des cotylédons de Sinapis alba en éclairement rouge Iointain continu.

Obtention of epinasty in the cotyledons of Sinapis alba under continuous far-red illumination. Relation to the development of hypocotyl and cotyledons. Treatment by far red light induces epinasty of the cotyledonary leaf. The effects of light treatments of different intensities were recorded for hypocotyl length, percentage of epinasty and the cotyledon leaf area. The percentage of epinasty increases as a function of treatment duration and light intensity. As from the second day of treatment a correlation is obtained between the percentage of epinasty and hypocotyl length when the seedlings are given far-red light treatment of different durations.     

How much water does a river need?

1. This paper introduces a new approach for setting streamflow-based river ecosystem management targets and this method is called the 'Range of Variability Approach' (RVA). The proposed approach derives from aquatic ecology theory concerning the critical role of hydrological variability, and associated characteristics of timing, frequency, duration, and rates of change, in sustaining aquatic ecosystems. The method is intended for application on rivers wherein the conservation of native aquatic biodiversity and protection of natural ecosystem functions are primary river management objectives.
2. The RVA uses as its starting point either measured or synthesized daily streamflow values from a period during which human perturbations to the hydrological regime were negligible. This streamflow record is then characterized using thirty-two different hydrological parameters, using methods defined in Richter et al . (1996). Using the RVA, a range of variation in each of the thirty-two parameters, e.g. the values at ± 1 standard deviation from the mean or the twenty-fifth to seventy-fifth percentile range, are selected as initial flow management targets.
3. The RVA targets are intended to guide the design of river management strategies (e.g. reservoir operations rules, catchment restoration) that will lead to attainment of these targets on an annual basis. The RVA will enable river managers to define and adopt readily interim management targets before conclusive, long-term ecosystem research results are available. The RVA targets and management strategies should be adaptively refined as suggested by research results and as needed to sustain native aquatic ecosystem biodiversity and integrity.     

DNA Biosynthesis in Chloroplasts: II. DEVELOPMENTAL VARIATION IN TTP INCORPORATION INTO DNA BY PLASTID EXTRACTS

Incorporation of [³H]TTP into DNA by pea chloroplast extractswas highly dependent on the age of the tissue from which plastidswere prepared. Catalytic activity was greatest in samples from6- to 9-d-old plants; preparations from more mature tissueswere much less effective. Moreover, activity was 3 to 10 timesgreater in younger tissues regardless of whether chlorophyll,protein or plastid number was used as the index of comparison.Enzymes from the first (oldest), second, third, and fourth (youngest)leaves of the same plants were also studied. Again, activitywas 4 to 10 times greater in samples from the youngest tissues.When plastid extracts from older leaves were mixed with thosefrom younger tissues, they did not reduce synthesis. Thus, thedecline in activity does not appear to be due to the productionof an inhibitor during plant development. One explanation forthese data is that enzymes of ctDNA replication, such as DNApolymerase, vary in activity during leaf development; thereforechanges in enzyme levels may be an important factor in controllingchloroplast DNA replication during development. We have alsoexamined the incorporation of [³H]TTP into DNA by isolated intactpea chloroplasts; in general, labelled TTP was less readilyincorporated into chloroplast DNA than was [³H]thymidine. Key words: Chloroplast DNA replication, chloroplast DNA polymerase     

ten-a overexpression causes abnormal pattern in the Drosophila compound eye

Ten-a is one of the two Drosophila proteins that belong to the Ten M protein family. This protein is a type Ⅱ transmembrane protein and is expressed mainly in the embryonic CNS, in the larval eye imaginal disc and in the compound eye of the pupa. Here, we investigate the role of ten-α during development of the compound eye by using the Gal4/ UAS system to induce ten-α overexpression in the developing eye. We found that overexpression of ten-α can perturb eye development during all stages examined. In an early stage, overexpression of ten-α in eye primordial cells caused small and rough eyes and interfered with photoreceptor cell recruitment, resulting in some ommatidia having fewer or extra photoreceptor cells. Conversely, ten-α overexpression daring ommatidial formation caused severe eye defects due to absence of many cellular components. Interestingly, overexpression of ten-α in the late stage developing ommatidial cluster affected the number of pigment cells, caused cone cells proliferation in many ommatidia, and caused some photoreceptor cell defects. These results suggest that ten-α may be a novel gene required for normal eye morphogenesis.     

Characterizing a zooplankton neighbourhood: small-scale patterns of association and abundance

• 1 This study compares small-scale (i.e. neighbourhood) associations among distributions of phytoplankton, zooplankton, and zooplankton grazing rates using a combination of correlations and analyses of spatial patchiness.
• 2 All zooplankton and phytoplankton populations had patchy distributions. On average, individuals experienced members of their same taxon at a density that was 42% greater than the mean sample density.
• 3 The various zooplankton taxa experienced different average neighbourhoods, even within the same stratum of the lake. For example, Daphnia galeata mendotae (Birge) experienced phytoplankton concentrations that were nearly 50% greater than those experienced by Daphnia pulicaria (Forbes) at the same depth.
• 4 The distributions of the various phytoplankton taxa were positively correlated with each other, but the distributions of zooplankton were negatively correlated, or more often, unrelated to each other.
• 5 Phytoplankton abundance was negatively correlated with zooplankton grazing rates.
• 6 We hypothesize that while phytoplankton distributions are driven by common external factors, the factors that determine horizontal distributions of zooplankton are species specific. In addition, zooplankton grazing appears at least partially responsible for the generation of patchiness in the distribution of phytoplankton.