A generic method of pesticide dose expression: Application to broadcast spraying of apple trees

The recommended dose for many pesticides is expressed as a constant mass or volume per unit ground area covered by the crop. This method of dose expression is well suited to boom spraying where a reasonably uniform horizontal distribution of deposit can be achieved with a well‐adjusted sprayer. However, in many practical situations (e.g. broadcast spraying of apple trees or other row structures where the spray application is made from within the canopy) the horizontal deposit distribution is strongly influenced by the crop area density and other crop structural parameters. This paper describes a generic method of pesticide dose expression to investigate these effects. The method incorporates a model of the spray volume deposition process. The model assumes that the pesticide deposit is proportional to the tank‐mix concentration of pesticide. The model also assumes that spray volume deposit is proportional to the applied spray volume per unit row length and is inversely proportional to a crop length scaling function L (i.e. a parameter with the units of length that is expressed as a generic function of different crop parameters). The useful working range of this model is bounded by the condition for high spray volume where target losses become significant due to saturation and the condition for very low volume where evaporative transport losses become significant. Within this framework, four different models are formulated using first‐order approximations for the length‐scale as functions of the following crop parameters: tree row spacing, tree row height, tree area density and tree row volume to ground area ratio. Published measurements of crop structure and spray volume deposit on apple trees are compared with the output from these models. Light detection and range (LIDAR) measurements of apple orchards are presented and used in conjunction with the different models to predict pesticide use associated with different methods of dose expression. The results demonstrate the relative potential for varying the pesticide application rate according to the different crop parameters. The results enable the identification of reference orchards that could be used to establish worst‐case pesticide application rates for registration purposes. The results also enable the identification of other orchards and growth stages where pesticide application rate might be reduced by up to a factor of five and give the same pesticide deposit as the reference structure.     

The Cell Cycle

I review recent advances in our knowledge of the eucaryoticcell cycle: the set of processes by which cells grow and divide.Genetic approaches to the cell cycle of somatic cells identifieda pathway of events where the initiation of each event was dependenton the successful completion of the preceding event, as wellas a single key gene, cdc2, that is required both at the beginningand at the end of the cell cycle. The alternative approach ofstudying the cell cycle biochemically in early embryos providedevidence for a cytoplasmic oscillator which alternated betweenmitosis-inducing and interphase-inducing states and identifiedthe mitosis-inducing component as maturation promoting factor(MPF). These two very different views of the cell cycle initiallyseemed irreconcilable. However, a link between the somatic andembryonic cell cycles was provided by the recent discovery thatthe cdc2 protein is one of the components of MPF. In the embryoniccell cycle the activation of MPF and induction of mitosis istriggered by the accumulation of a protein named cyclin whichbecomes a component of MPF. Somehow, MPF induces the proteolyticdegradation of cyclin, which inturn allows MPF to be inactivatedand allows the cell cycle to pass from mitosis into interphase.The more complex cell cycle of somatic cells is probably derivedfrom the embryonic cyclin-based oscillator by imposing a systemof checks and balances on the accumulation and destruction ofcyclin. I also present some thoughts on the relationships between scienceand society, and comment on the way in which scientists describetheir work to the lay world.     

Shock Pulse Effects on Wheat Growth

Wheat seedlings (Triticum aestivum cv. Pacific Blue Stem) grown under continuous low-level illumination were used to study the effects of pressure variation and its duration. Growth was determined by dry weights, leaf length, and types of secondary roots produced. Two sublethal shock pulses (1.41 and 2.82 kg cm ^?2) and three pressure duration intervals (0.1, 1.0 and 10.0 seconds) were studied. The results indicated a general overall reduction in growth associated with the shock pulse and that the pressure duration interval influenced the shock- growth response. The long pressure duration interval was found to be the most influential on shock pulse response. Present knowledge indicates that a pulse rise-time of 1 ms and a pressure duration interval of at least 1.0 second affect plant growth at sublethal shock pulses, such that the growth response is linear or bi-directional, depending on the magnitude of the shock pulses, and either linear or complex with respect to pressure duration interval for any shock pulse level.     

Visual fields in Blue Ducks Hymenolaimus malacorhynchos and Pink-eared Ducks Malacorhynchus membranaceus: visual and tactile foraging

Blue Ducks Hymenolaimus malacorhynchos (Anatidae), an IUCN Red Listed Endangered species, reside in headwaters of New Zealand rivers and feed primarily on aquatic invertebrates. However, whether such food items are detected by tactile or visual cues is unknown. That Blue Ducks may use tactile cues when foraging is suggested by the presence of specialized flaps of thickened, keratinized epidermis containing Herbst's corpuscles along the ventral margins of the upper mandibles near the bill tip. Similar bill flaps are found only in one other duck species, Pink-eared Ducks Malacorhynchus membranaceus , that surface filter-feed on a range of planktonic organisms. Using an ophthalmoscopic reflex technique we determined the visual fields of both species. In Blue Ducks the eyes are frontally placed resulting in a relatively wide binocular field into which the narrow tapering bill intrudes. There is a large blind area to the rear of the head. This visual field topography is similar to that of other visually guided foragers including those that take mobile prey from the water column, e.g. penguins (Spheniscidae). By contrast, Pink-eared Duck visual fields show features found in other tactile feeding ducks: a narrow frontal binocular field with the bill falling at the periphery, and comprehensive visual coverage of the celestial hemisphere. We conclude that although Blue Ducks may take prey from rock surfaces they are primarily visual feeders of the water column and we suggest therefore that their foraging may be significantly disrupted by changes in water clarity. This introduces a previously unconsidered factor into the selection of sites for population enhancement or re-introductions, a current conservation focus.     

Periphyton biomass dynamics in gravel bed rivers: the relative effects of flows and nutrients

SUMMARY. 1. Periphyton chlorophyll a and ash free dry weight (AFDW) were monitored in nine rivers to examine the relative importance of flows and nutrients for regulating periphyton biomass in gravel bed rivers. 2. Mean annual flows in the rivers ranged from 0.94 to 169 m³ s^?1, mean dissolved reactive phophorus (DRP) from 1.3 to 68 μ g 1^?1, periphytic chlorophyll a from 4.6 to 73 mg m ^?2. and AFDW from 2.8 to 16 g m^?2. 3. For eight of the nine rivers NH₄-N. DRP, total Kjeldahl nitrogen, total phosphorus and total suspended solids were correlated (P<0.01) with flow, and for seven rivers conductivity was inversely correlated (P<0.05) with flow. 4. There was a hyperbolic relationship between flows and biomass, with chlorophyll a >100 mg m ^?2 and AFDW >20 g m^?2 occurring most frequently in flows of <20 m³ s^?1. 5. Floods prevented the development of medium term (i.e. up to 2 months) maxima in biomass in five of the rivers, but maxima occurred over summer-autumn and winter-spring in the three rivers where floods were absent. 6. Chlorophyll a biomass was more resistant to flooding than AFDW. Only 5993 of the forty-six recorded floods caused chlorophyll a scouring, whereas 74% of the floods caused AFDW scouring. The efficiency of scour was more influenced by the pre-flood biomass than the magnitude of the event. 7. Biomass maxima were significantly correlated (P<0.01) with mean DRP concentration during the accrual period. Overall, up to 53% of the mean annual biomass difference between rivers was explained by the mean annual DRP concentrations. However, the high correlations between nutrient concentrations and flow indicated that the nutrient data were also carrying hydrological information and that simple causal relationships between nutrients and biomass are difficult to establish in rivers. 8. It is concluded that hydrological factors contribute at least equally with nutrients to the differences in periphyton biomass between the gravel-bed study rivers. They combined to explain up to 63.3% of the variance in biomass, compared with 57.6% for nutrients. It is recommended that periphyton data from gravel-bed rivers should always be viewed within the context of the flow history of the site, and not just as a function of nutrient concentrations.     

The use of experimental palaeontology in reproducing the effects of diagenetic flattening on graptolites

The detailed effects of diagenetic flattening on the graptolitc rhabdosomc have been investigated experimentally. The initial procedure, to test the effects of flattening on cylinders constructed from a variety of semi-brittle to plastic materials when compressed in a plaster 'matrix', demonstrates that a degree of rigidity is necessary to prevent lateral spread on diagenetic compression, even when lateral confining pressures are present. A second experiment demonstrates conclusively that the effects of flattening on the thecal style of Dicellograptus complanatus proposed by Briggs & Williams (1981; Lethaia 14) can be simulated. A model of an aseptate diplograptid produced a median depression when compressed but no preservational 'median septum', which is considered to be produced in several diplograptid taxa. It is shown that some diplograptids spread laterally along a median line when flattened in scalariform orientation although this has not yet been achieved experimentally owing to the high degree of compression required. □ Graptolithina, diagenesis, flattening,     

Separation of Individual Stages of Trypanosoma cruzi Grown in Cell Culture by Continuous Free-Flow Electrophoresis

The separation of extracellular protozoan parasites from host cells based on a difference in surface charge has been described. However, with Trypanosoma cruzi no method exists for the isolation of pure parasite stages from heterogeneous mixtures. Studies on the electrophoresis of mixed stage populations confirm significant surface charge density differences exist among epimastigotes, trypomastigotes, and amastigotes. In ascending order of electronegativity, amastigotes have the lowest charge density, try-pomastigotes next, followed by epimastigotes. A technique has been developed for the separation of purified populations of parasites based on these charge differences using a continuous free-flow electrophoresis apparatus. The separated populations are morphologically intact and maintain their infectivity to mice. This separation method is applicable for preparative and analytical isolation of pure stages of T. cruzi for biochemical and immunological studies.     

Nonequilibrium kinetics of a cyclic GMP-binding protein in dictyostelium discoideum

Chemoattractants added to cells of the cellular slime mold dictyostelium discoideum induce a transient elevation of cyclic GMP levels, with a maximum at 10 s and a recovery of basal levels at approximately 25 s after stimulation. We analyzed the kinetics of an intracellular cGMP binding protein in vitro and in vivo. The cyclic GMP binding protein in vitro at 0 degrees C can be described by its kinetic constants K(1)=2.5 x 10(6) M(- 1)s(-1), k(-1)=3.5 x 10(-3)s(-1), K(d)=1.4 x 10(-9) M, and 3,000 binding sites/cell. In computer simulation experiments the occupancy of the cGMP binding protein was calculated under nonequilibrium conditions by making use of the kinetic constants of the binding protein and of the shape of the cGMP accumulations. These experiments show that under nonequilibrium conditions by making use of the kinetic constants of the binding protein and the shape of the cGMP accumulations. These experiments show that under nonequilibrium conditions the affinity of the binding protein for cGMP is determined by the rate constant of association (k(1)) and not by the dissociation constant (k(d)). Experiments in vivo were performed by stimulation of aggregative cells with the chemoattractant cAMP, which results in a transient cGMP accumulation. At different times after stimulation with various cAMP concentrations, the cells were homogenized and immediately thereafter the number of binding proteins which were not occupied with native cGMP were determined. The results of these experiments in vivo are in good agreement with the results of the computer experiments. This may indicate that: (a) The cGMP binding protein in vivo at 22 degrees C can be described by its kinetic constants: K(1)=4x10(6)M(-1)s(-1) and K(-1)=6x10(-3)s(-1). (b) Binding the cGMP to its binding protein is transient with a maximum at about 20-30 s after chemotactic stimulation, followed by a decay to basal levels, with a half-life of approximately 2 min. (c) The cGMP to its binding proteins get half maximally occupied at a cGMP accumulation of δ[cGMP](10)=2x10(-8) M, which corresponds to an extracellular stimulation of aggregative cells by 10(-10) M cAMP. (d) Since the mean basal cGMP concentration is approximately 2x10(-7) M, the small increase of cGMP cannot be detected accurately. Therefore the absence of a measurable cGMP accumulation does not argue against a cGMP function. (e) There may exist two compartments of cGMP: one contains almost all the cGMP of unstimulated cells, and the other contains cGMP binding proteins and the cGMP which accumulates after chemotactic stimulation. (f) From the kinetics of binding, the cellular responses to the chemoattractant can be divided into two classes: responses which can be mediated by this binding protein (such as light scattering, proton extrusion, PDE induction, and chemotaxis) and responses which cannot be (solely) mediated by this binding protein such as rlay, refractoriness, phospholipids methylation, and protein methylation.     

Effects of Moderate Water Deficit (Stress) on Wheat Seedling Growth and Plastid Pigment Development

Etiolated 6-day-old wheat (Triticum aestivum L. cv. Chris) seedlings were subjected to osmotic stress by an application of polyethylene glycol 12 h prior to the exposure to a continuous 72-h light period. The water potential of the primary leaf of stressed seedlings was between –9 and –14 bars throughout the light period. Stress impaired seedling growth, leaf unfolding, and the increase in leaf area. The imposed osmotic stress reduced total chlorophyll accumulation, particularly after 9 h light, suggesting that this is the approximate time period for the depletion of the protochlorophyll(ide) pool and the pool of an essential protochlorophyll(ide) precursor. The chlorophyll a/b ratio of extracts from stressed and non-stressed plants was the same during the 72-h greening period. Water deficit stress impaired carotenoid accumulation sooner than the impairment of chlorophyll production suggesting either a smaller carotenoid pool size of precursors or that the metabolic pathway of carotenoid synthesis was more sensitive to stress. Shifts from the usual plastid pigment absorbance maxima were not observed in these studies.     

Immunoreactive Parathyroid Hormone in Circulation of Man

WE have reported that parathyroid hormone (PTH) is secreted from the parathyroid in vivo as a polypeptide of eighty-four amino-acids, identical to the hormone stored in the glands (molecular weight of 9,500), but that the hormonal polypeptide is cleaved after it enters the general circulation¹. A large hormonal fragment from this cleavage, with a molecular weight of approximately 7,500, has been identified in the circulation. The fragment differs immunologically from the hormone secreted and extracted from the glands¹. To analyse the biological significance of the metabolism of the hormone and the chemical nature and hormonal activity of the large circulating fragment, we have developed radioimmunoassays that specifically measure the amino-terminal (N-assay) and carboxyl-terminal (C-assay) regions of the hormonal molecule. We now report that much higher concentrations of immunoreactive hormone are found in the general circulation by the C-assay than by the N-assay. The studies with the N-assay indicate that the large fragment has lost a portion of the amino-terminal sequence required for biological activity⁹. Since the fragment is present in much higher concentration than native uncleaved hormone, we must conclude that much of the immunoreactive PTH detected in the circulation is biologically inactive.