Translocation of Nitrogenous Compounds in Symbiotic and Nitrate-Fed Amide-Exporting Legumes

Peoples, M. B., Sudin, M. N. and Herridge, D. F. 1987. Translocationof nitrogenous compounds insymbiotic and nitrate-fed amide-exportinglegumes.–J. exp. Bot. 38: 567–579. The transport of nitrogen from the roots and nodules of chickpea(Cicer anetinum L.), lentil (Lens culinaris Medic), faba bean(Vicia faba L.) and pea (Pisum sativum L.) was examined in glasshouse-grownplants supplied either with nitrate-free nutrients or with nutrientssupplemented with 1,2,4 or 8 mol m^-3153N-nitrate. A sixth treatmentcomprised uninoculated plants supplied with 8–0 mol m^-31513N-nitrate. For each species, more than 75% of the nitrogenwas exported from the nodules as the amides, asparagine andglutamine. In fully symbiotic plants, the amides also dominatednitrogen transport to the shoot When N2 fixation activity wasdecreased by the addition of nitrate to the rooting medium,the N-composition of xylem exudate and stem solutes changedconsiderably. The relative concentrations of asparagine tendedto increase in the xylem whilst those of glutamine were reduced;the levels of nitrate increased in both xylem exudate and thesoluble nitrogen pool of the stem with a rise in nitrate supply.The changes in relative nitrate contents reflected generallythe contributions of root and shoot to overall nitrate reductaseactivity at the different levels of nitrate used. The relationshipsbetween the relative contents of xylary or stem nitrate andamino nitrogen and the plants' reliance on N2 fixation (determinedby the ¹⁵N isotope dilution procedure) were examined. Data suggestthat compositional relationships based on nitrate may be reasonableindicators of symbiotic dependence for all species under studyexcept faba bean when greater than 25% of plant nitrogen wasderived from N2 fixation. Key words: Nitrogen, translocation, legumes     

A new citrus-feeding psyllid from the Comoro Islands, with a review of the Diaphorina amoena species group (Homoptera)

ABSTRACT. Analysis of host plant data for the seventy-one species of Diaphorina shows the genus to be unusually polyphagous, the species developing on eighteen families of dicotyledonous angiosperms. Apart from the common Asian citrus pest, Diaphorina citri , a second citrus-feeding species is described and discussed. This species belongs to the amoena species-group which is defined and a key to nine of the ten included species is given. Seven new species are described: flavipennis sp.n. and nigripennis sp.n. from East Africa on Strychnos usambarensis; huila sp.n. from Angola on Ptaeroxylon obliquum; turned sp.n., from South Africa (host unknown); orantimina sp.n. from Madagascar (host unknown); auberti sp.n. from Comoro Islands on citrus trees; and bispinulata sp.n. from Madagascar (host unknown).     

The dispersal unit of Dacrycarpus dacrydioides (A. Rich.) de Laubenfels (Podocarpaceae) and the significance of the fleshy receptacle

FOUNTAIN, D. W., HOLDSWORTH, J. M. & OUTRED, H. A., 1989. The dispersal unit of Dacrycarpus dacrydioides (A. Rich.) de Laubenfels (Podocarpaceae) and the significance of the fleshy receptacle. Dacrycarpus dacrydioides (formerly Podocarpus dacrydioides ) is an arborescent gymnosperm endemic to New Zealand. The high water content (43%) and sensitivity of viability towards desiccation, suggest the seeds are of the 'recalcitrant' type. The 'fruits' comprising a seed borne on a fleshy receptacle arc shed in large numbers. The development of the seed precedes the full development of succulence in the receptacle and at maturity the seed has a high relative water content (RWC) relative to the receptacle. Within the maturing reproductive unit, the receptacle buffers the seed against the effects of water stress. After shedding, seeds are rapidly desiccated in moving air, and viability is impaired below approximately 80"' RWC and abolished at 34", seed RWC. The presence of the receptacle during drying confers resistance to desiccation-associated damage. Five phases of desiccation sensitivity are distinguished in recognition of the protective role of the receptacle. It is suggested that the advantages associated with prolonging seed viability may have contributed to the evolutionary development of succulence in the reproductive unit. This might be considered as a selection pressure in a manner similar to the proposal that such fleshy structures are associated with seed dispersal by birds.     

Development of Vacuolar Volume in the Root Tips of Pea

Cell and vacuole areas were measured by light microscopy inlongitudinal and transverse sections cut at 0.4-mm intervalsalong the apical 7.2 mm of the primary root of pea. The vacuolararea (or volume) fraction — that is, vacuole area (orvolume) divided by cell area (or volume) — increased fromabout 15 % in cells 0.4 mm from the distal boundary of the apicalmeristem (the cap /root junction), to about 85% in cells situated6.8–7.2 mm from that boundary. At each distance, vacuoledevelopment tended to be greater in the cortex than in the stele.Vacuoles occupied about 22% of the tissue volume in the first1 mm length of root (measured from the cap/root junction), about31 % of the tissue volume in the first 2 mm, and about 45% whensummed over the apical 5-mm length of root. Phosphorus supplyor deprivation produced only minor and non-significant changesin vacuole development. The results have implications affectingprevious estimates of cytoplasmic and vacuolar phosphate concentrationsin pea root tips. Pisum sativum L., pea, root, vacuole, volume     

Seasonal dynamics of invertebrate drift in a Hong Kong stream

Drift samples were taken with paired nets on 19 occasions over a 12-month period in Tai Po Kau Forest Stream (TPKFS), Hong Kong. Mean drift density (±1 S.E.) was 277·9 ± 25·0 individuals 100 m^-3; peaks in density were apparent during autumn and spring. One hundred and two taxa were recovered from the drift, and the total number of taxa drifting was positively related to water temperatures. Over 99% of the aquatic animals collected in drift samples were insects, 10 taxa of which constituted 67·3% of the entire catch. Baetid mayflies dominated the composition of the drift, comprising 40·4% of individuals caught.
Seasonal changes in the drift of individual taxa were evident, reflecting significant relationships between drift densities and water temperature: Simulium T₁ (Diptera). Anisocentropus maculatus (Trichoptera) and Amphinemura chui (Plecoptera) drifted most in winter, whereas Chimarra T₁, Polymorphanisus astictus (Trichoptera), Helodes #1 and cf. Rhantus sp. (Coleoptera) were most numerous in summer. Drifting mayflies showed spring ( Indobaetis sp., Cinygmina T₁, Serratella T₂), autumn ( Baetiella sp., Pseudocloeon T₂), or spring and autumn ( Baetis nr pseudofrequentus ) peaks which were not clearly related to water temperature. In only two cases ( A. maculatus and P. astictus ) was TPKFS drift seasonality associated with life-cycle events. Overall, there was no evidence of community-level trends in the periodicity of stream drift in this seasonal tropical habitat.     

Carbon isotopes as indicators of elephant diets and African environments

Stable carbon isotope ratios have been successfully used to assess modern animal diets and to reconstruct prehistoric diets of animals and humans (Vogel & van der Merwe, 1977; van der Merwe & Vogel, 1978; Burleigh & Brothwell, 1978; Vogel, 1978a; DeNiro & Epstein, 1978; Tieszen et al., 1979; Tieszen & Imbamba, 1980; Chisholm, Nelson & Schwarcz, 1982; Tauber, 1981). We have used ¹³C/¹²C ratio measurements of bone collagen to study the diets of African elephants in twelve wildlife refuges. These represent most of the habitats in which elephants live, including such diverse plant communities as primary rain forest, savanna woodland and desert. The δ¹³C values were found to have a simple linear relationship with tree density in most cases. When translated into relative amounts of dietary browse (C₃ plants) and graze (C₄ plants), the grass content is seen to be systematically under-represented, presumably due to inefficient metabolism. This does not affect the relationship between elephant diet and tree density, which has implications for the study of elephant-woodland interactions, and for reconstructions of past African environments.     

Ecological and evolutionary implications of diet in monitor lizards

A survey of 35 species indicates that monitor lizards (Varanus) typically hunt over large areas, search in particular microhabitats, and feed frequently on a wide variety of prey, many of which are relatively small. There is ontogenetic, seasonal, and geographic variation in diet. With some exceptions, invertebrates are the predominant prey, but rare predation on vertebrates is often energetically significant. A few monitors specialize on prey types that occur as occasional items in the diet of species with more generalized diets; these include crabs, snails, orthopterans, lizards, and large mammals. For most species, prey specialization occurs via habitat selection and a variety of prey types and sizes are eaten, as expected for widely searching predators. Comparisons with other anguimorphans suggest that derived features of Varanus are associated with high body temperature and activity levels; specialized chemoreception; and rapid, skillful capture of hidden and/or potentially hard to catch prey. Occasional ingestion of moderately large prey is primitive for Varanoidca (Helodermatidae +Varanidae), accentuating a trend that is perhaps primitive for anguimorphan lizards. Reduction of very large prey prior to ingestion is a derived attribute within Varanus , seen infrequently in several larger species and commonly in V. komodoensis. This study illustrates the synthesis of comparative natural history in a phylogenetic context, a method that addresses the history of organismal change.     

拟澳洲赤眼蜂生殖系统的研究

拟澳洲赤眼蜂(Trichogramma confusum)的体长约0.6mm,腹部长度约0.3mm.雌蜂生殖系统(包括卵巢、生殖腔、受精囊及三种附腺)位于腹部后端,约占腹腔的2/3.成熟的卵巢由两条多滋式的卵巢管组成.两条成熟卵巢的端段细长,扭卷成一条疏松索,基部膨大,内脏贮存大量卵粒.成对的侧输卵管较短,分别开口于生殖腔后方的两侧,中输卵管缺如.受精囊呈梨形,开口于生殖腔后方.雌性生殖系统三种附腺中,第一种附腺是成对的,呈锤状,分别连接于生殖腔前方两侧;第二种附腺,腺体呈球状,其前端以短曲的小管通进膨大的贮腺囊,贮腺囊端部成柄状的弯曲小管,连接于产卵管的基部开口处.第三种附腺的腺体呈棒状,前端为细长的小管,开口于第二种附腺贮腺囊的前端.雄性生殖系统由成对的睪丸,输精管、贮精囊、附腺及单一的射精管组成.蛹的早期到后期至成虫期睾丸的形态结构,各有不同变化.