Regulation of Sulphate Transport in a Tropical Legume, Macroptilium atropurpureum, cv. Siratro

When young plants of Macroptilium atropurpureum, cv. Siratrowere deprived of external sulphate (-S plants) growth of shootsand roots continued at rates comparable to those in plants wellsupplied with sulphate (control) for 3 d and 5 d respectively.Dilution of internal sulphur therefore took place and redistributionof sulphur occurred between inorganic and organic forms andbetween roots and younger leaves. Even when S-deficiency limitedgrowth, plants contained 16% of their total sulphur as sulphate,but most of this was retained in old leaves and redistributedslowly to growing zones. The capacity for sulphate uptake increased in roots of –Splants very soon after they were deprived of external sulphate;within 24 h the absorption from 0.25 mol m^–3 SO₄^2–was more than five times that of control roots. Maximum increasedcapacity was reached after 2–3 d stress when the V_maxof system 1 was 1948 nmol h^–1g^–1root fr. wt. in–S plants and 337 nmol h^–1g^–1root fr. wt.in controls. The K^mfor system 1 did not change significantlywith S-stress being between 5–8 µM in both setsof plants. Absorption of L-cysteine was not stimulated by S-stress. There was a close, positive relationship between plant growthrate and the rate at which sulphate uptake capacity was enhancedby withholding sulphate from culture solutions. When –S plants were replaced in sulphate-containing solutiontheir capacity for SO₄^2– declined to the control levelwithin 24 h. Very marked repression of capacity was also foundwhen –S plants were treated with L-cysteine, but therewas no immediate effect with methionine. Roots of this species appear to have a very active system fordegrading L-cysteine to sulphate, 30% of the label in ³⁵S-cysteineabsorbed by roots was recovered in ³⁵SO₄^2– after 20 minor 2 h incubation. By contrast, roots had a very weak abilityto reduce sulphate. When part of the root system was in solution lacking sulphatethere was enhanced uptake of sulphate by other parts which themselveswere amply supplied with sulphate. This is seen as an exampleof compensatory absorption. The response to S-stress is specific and there were no positiveinteractions between S-stress and the absorption of phosphate,or P-stress and the uptake of sulphate. The results are discussed in relation to the close control ofsulphate uptake by internal sulphate concentration, redistributionof forms of sulphur during stress and mobility of sulphate inthe phloem. Key words: Kinetics, Amino-S, Sulpholipid, Repression;, Deficiency     

Primary productivity studies during early years of West Point Reservoir, Alabama-Georgia

SUMMARY. 1. Phytoplankton density (organisms ml^?1), standing crop (chlorophyll a mg m^?2) and primary productivity (mg C m^?2 d^?1) were measured during years 2 (1976) to 5 (1979) after impoundment on West Point Lake. 2. West Point waters had low alkalinity (<0.4 meq 1^–1) and low conductivity (<75 μs cm^?1 at 20°C) but N and P concentrations typically exceeded those considered apt to cause nuisance blooms of algae. Abiogenic turbidity was normally higher in the upstream areas of the reservoir than in the downstream areas and was several times higher in winter-spring than in summer-autumn due to increased rains and runoff. 3. Primary productivity varied greatly both temporally and spatially. A mean value of 684 mg C m^?2 d^?1 was well within the mesotrophic range and did not approach the highly eutrophic state predicted. Productivity increased from a low of 550 mg C m^?2 d^?1 in 1976 to high of 763 mg Cm^?2d^?1 in 1979. 4. Observed variation in both chlorophyll a and primary productivity was more predictable in the cool (December-March) than in the warm (June-September) season and with plant nutrient data than without it. With plant nutrient data in the cool season 84% and 86% of the variation (R²) in chlorophyll a and productivity, respectively, were accounted for by the regression equations. During the warm season, with plant nutrient data, regression equations accounted for 44% and 68% of the variation in chlorophyll a and productivity, respectively. Higher R² values in cool seasons resulted from the overriding influence of abiogenic turbidity on phytoplankton communities.     

Aggression and Mating Success in Three Species of Drosophila1

Three closely related species of Drosophila: D. virilis, D. americana, and D. novamexicana, are known to differ in levels of male-male aggression. Through direct observation in the laboratory, we attempted to determine and characterize the relationships between intrasexual aggression and mating success in males of each of these species. Our results indicated that the most important determinant of male mating success was not the amount of aggression performed by a male, but rather the amount of aggression directed towards him.     

Father's Water equals Mother's Milk: The Conception of Parentage in Kaliai,West New Britain

This paper describes the traditional and modern ideology of conception and parenting among the Kaliai of West New Britain Province, Papua New Guinea. A pervasive set of beliefs hinges on male primacy and includes the assignment of the principal role in conception to the male. Females become kin to the children they bear only secondarily, through nurturance of their infants. Mother's milk and semen, then, are equivalent in their capacity to establish links of kinship. Despite the ideology of male dominance, food given is so loaded with significance for the establishment of kin ties that adoptive parents, male and female, must feed a nursing mother or risk the lapse of their claim on her infant. A mother's milk is therefore truly equal to a father's semen — his ‘water’ — and different aspects of Kaliai ideology are used more to justify past behaviour rather than to constrain it in the present.     

Effects of Growth and Assay Temperatures on Unidirectional K+ Fluxes in Roots of Rye (Secale cereale)

The effects of growth and assay temperature on unidirectionalK⁺ fluxes in excised roots of rye (Secale cereale cv. Rheidol)were studied using ⁸⁶Rb⁺ as a tracer. Both K⁺ influx to thevacuole, estimated as K⁺ uptake between 3 and 12 h after transferof unlabelled roots to radioactive solution, and movement ofK⁺ to the xylem were determined directly. Other fluxes weredetermined on excised roots of plants, which had been labelledwith ⁸⁶Rb⁺ since germination, by conventional triple exponentialefflux analysis. When assayed at 20°C, roots of plants previously grown at20°C(WG roots) had lower rates of net K⁺ uptake than rootsof low temperature-acclimated plants, grown with a temperaturediferential between roots (87°C) and shoots (20°C) eithersince germination (DG roots) or for 3 d prior to experiments(DT roots). This resulted from a greater unidirectional K⁺ effluxacross the plasma membrane and a reduced K⁺ flux to the xylemin WG roots, compared to DG or DT roots, rather than a decreasein unidirectional K⁺ influx or a decrease in the net K⁺ fluxto the vacuole. Indeed, although WG roots had lower rates ofK⁺ influx and K⁺ efflux across the tonoplast at 20°C thanDG or DT roots, roots of plants from all growth temperaturetreatments showed an equivalent net K⁺ flux to the vacuole. Although all unidirectional K⁺ fluxes in roots from plants grownunder all temperature regimes were reduced by lowering the temperatureof the root, these fluxes were differentially affected in rootsof plants from contrasting growth temperature treatments. Rapidcooling to 8°C of WG roots resulted in a lower rate of K+influx and a transient increase in K⁺ efflux across both theplasma membrane and tonoplast, compared to DG and DT roots.Furthermore, since the K⁺ flux to the xylem was lower in WGroots, the net K⁺ uptake at 8°C into WG roots was considerablyreduced compared to DG and DT roots. These results suggest thatlow temperature-acclimation of K⁺ fluxes in rye roots may involvea reduction in the temperature sensitivity of K⁺ influx anda curtailment of K⁺ efflux across both the plasma membrane andtonoplast at low temperatures. Key words: K⁺influx, K⁺ efflux, low temperature, potassium, rye (Secale cereale cv. Rheidol)     

Temperature-induced Changes in the Synthesis of Unsaturated Fatty Acids by Acanthamoeba castellanii

ABSTRACT. Major fatty acid components of Acanthamoeba castellanii lipids extracted after growth at 30°C include myristate, palmitate, stearate and the polyunsaturates linoleate, eicosadienoate, eicosatrienoate and arachidonate, with oleate as the sole major monounsaturated fatty acid. By comparison, growth at 15°C gave increased linoleate, eicosatrienoate and arachidonate, but decreased oleate and palmitate. When the growth temperature was shifted downwards from 30°C to 15°C, increased lipid unsaturation occurred over a period of 24 h; thus decreases of oleate and eicosadienoate were accompanied by increases in linoleate, eicosatrienoate, arachidonate and eicosapentaenoate. An upwards shift from 15°C to 30°C gave negligible alterations in fatty acid composition over a similar period. At 15°C organisms rapidly use [1-¹⁴C] acetate for de novo fatty acid synthesis; stearate is converted via oleate to further desaturation and chain elongation products. Similar short term experiments at 30°C indicate only de novo synthesis and Δ9-desaturation; synthesis of polyunsaturates was a much slower process. Rapid incorporation of [1-¹⁴C] oleate at 30°C was not accompanied by metabolic conversion over two hours, whereas at 15°C n-6 desaturation to linoleate was observed. Temperature shift of organisms from 15°C to 30°C in the presence of [1-¹⁴C] acetate revealed that over half of the fatty acids in newly-synthesised lipids were saturated, but the proportions of unsaturated fatty acids increased with time until the total polyenoate components reached 17% after 22 h. A shift of temperature in the reverse direction gave a corresponding figure of 60% for polyunsaturated fatty acids. These results emphasize the importance of n-6 desaturation in the low temperature adaptation of Acanthamoeba castellanii .     

Colonization of pasture by Kunzea ericoides in the Tidbinbilla Valley,ACT, Australia

Stand morphometry and age structure were analysed for populations of burgan, Kunzea ericoides, which were colonizing pastoral land in the Tidbinbilla Valley, Australian Capital Territory. Three types of stands, (i) closed burgan-dominated; (ii) open burgan-dominated; and (iii) mixed burgan and eucalypts, were compared at each of two locations. Burgan ages were determined from growth ring counts cross-correlated with seasonal rainfall and annual increments in Pinus radiata. Burgan stands have developed from windblown seed coming from nearby forest margins and drainage-lines. The species colonized rural lands in the Tidbinbilla Valley rapidly from the early 1960s, when changes in land use practices occurred which enabled sparse colonists to contribute to rapid population expansion. Colonization was initially slow, but recruitment increased dramatically in the early 1960s in closed and open stands when densities were between 0.01 and 0.03 plants m^-2. These stands did not follow classic secondary succession, as the differences between stands sampled were largely the result of differences in burgan density and floristic composition of the sites at the time of change in land use practices. These differences in turn influenced the phenotypic response of individual plants and the ensuing stand structures. A closed shrub canopy of burgan, together with the species self-replacement strategies, is likely to prevent other species from entering the closed burgan sites and becoming dominant. Where the objective is to limit the spread of burgan, isolated plants, which act as foci for spread, would be the primary target for control.     

All-female broods and mimetic polymorphism in Acraea encedon (L.) (Lepidoptera: Acraeidae) in Tanzania

In some populations of the African butterfly, Acraea encedon, there are two kinds of females, one producing offspring in a normal 1:1 sex ratio, the other producing females only; in other populations the sex ratio is apparently normal. All-female broods had hitherto been mainly associated with populations in which field sampling revealed an excess of females. The all-female brood trait is described from a population at Dar es Salaam which field sampling suggested was normal, and this indicates that the trait may be much more widespread and common than had previously been supposed. This discovery also extends the known distribution of the trait across Africa from Sierra Leone to eastern Tanzania. The butterfly is also a polymorphic Müllerian mimic of Danaus chrysippus, which is a highly unusual phenomenon as Müllerian mimicry is almost invariably monomorphic. The relative frequencies of two corresponding colour forms of the two species of butterflies at Dar es Salaam adds support to the hypothesis that they are indeed Mullerian mimics. The results of breeding experiments suggest that the polymorphic forms in Acraea encedon are allelic with dominance.     

Proliferation of Maize (Zea mays L.) Roots in Response to Localized Supply of Nitrate

Maize (Zea mays L.) plants with two primary nodal root axeswere grown for 8 d in flowing nutrient culture with each axisindependently supplied with . Dry matter accumulation by roots was similar whether 1.0 mol m^–3 was supplied to on( or both axes. When was supplied to only one axis, however, accumulationof dry matter within the root system was significantly greaterin the axis supplied with . The increased dry matter accumulation by the +N-treated axis was attributableentirely to increased density and growth of lateral branchesand not to a difference in growth of the primary axis. Proliferation of lateral branches for the + N axis was associatedwith the capacity for in situ reduction and utilization of aportion of the absorbed , especially in the apical region where lateral primordia are initiated. Althoughreduced nitrogen was translocated to the –N axis, concentrationsin the –N axis remained significantly lower than in the+N axis. The concentratio of reduced nitrogen, as well as invitro reductase activity, was greater in apical than in more basal regions of the +N axis. The enhancedproliferation of lateral branches in the + N axis was accompaniedby an increase in total respiration rate of the axis. Part ofthe increased respiration was attributable to increased massof roots. The specific respiration rate (umol CO₂ exolved perhour per gram root dry weight) was also greater for the +N thanfor the –N axis. If respiration rate is taken as representativeof sink demand, stimulation of initiation and growth of lateralsby in situ utilization of a localized exogenous supply of establishes an increased sink demand through enhancedmetabolic activity and the increased partitioning of assimilatesto the + N axis responds to the difference in sink demand between+N and –N axes. Key words: NO₃^- reduction, NO₃^- uptake nitrogen partitioning, root respiration, sink demand