Developmental Endocrinology of the Dipnoan, Neoceratodus forsteri

The development of the pineal, pituitary and thyroid glandsof the extant lungfish, Neoceratodus forsteri, are being studiedboth morphologically and functionally. This paper presents datafrom hatching to 40–52 weeks for a standardised seriesof lungfish, bred at Macquarie University. At hatching, thepineal comprises a single organ attached to the roof of thediencephalon, with well-developed photoreceptor, supportingand ganglion cells. The photoreceptors gradually degenerate,giving way to secretory cells which contain electron dense granules.These latter are immunoreactive to melatonin antibodies anddigestable with protease. The pituitary at hatching comprisesa hollow ball of cells lying beneath the infundibular regionof the hypothalamus. Ultrastructurally, four cell types canbe distinguished by cytoplasmic granule size after the firstfour weeks of development posthatching. By 20 weeks, a furtherthree cell types are recognisable. Inununogold labelling hasidentified corticotropes and melanotropes at four weeks and,at 20 weeks, prolactin cells, thyrotropes and somatotropes alsocan be identified. The thyroid is only just apparent at hatching,containing 2–3 follicles. Thenumbers of follicles increasesgradually, and variably between animals, with age. Iodine uptakein methimazole-treated animals did not exceed that of controlsat any of the three stages tested, indicating a lack of feedbackcontrol between thyroid hormones and pituitary thyrotropes at,or before, 40 weeks of age. Thyroid hormone receptors in theliver at 40 weeks are predominantly immunoreactive to humanTRac antibodies. These findings taken together suggest that,up to 40 weeks post hatching, lungfish development is equivalentto amphibian premetamorphic development. This would be consistentwith lungfish neoteny, but cannot be taken as evidence for neotenyuntil confirmed at later stages of development     

Factors involved in resistance to blight (Phytophthora infestans (Mont.) de Bary) in potatoes and assessment of resistance using detached leaves

In leaves of potatoes inoculated with Phytophthora infestans early in the growing season, more but smaller lesions with later onset of sporulation and fewer sporangia developed than on those inoculated later. None of these factors was uniform on detached leaves of all clones, so could not be used separately to forecast field resistance satisfactorily; when considered together, a reasonable prediction was feasible. With some clones, tests of detached leaflets gave a better indication of behaviour in the field than laboratory tests of whole plants.     

Seasonal variation in freezing tolerance of the New Zealand alpine cockroach Celatoblatta quinquemaculata

1. The cold hardiness of the alpine cockroach Celatoblatta quinquemaculata was investigated. This species is found at 1360 m a.s.l. beneath schist slabs on the Rock and Pillar Range (Central Otago, New Zealand). Cockroaches were collected monthly from January to December 1996, and their LT₅₀ and supercooling points determined.
2. Celatoblatta quinquemaculata was freezing tolerant throughout the year, with a lower lethal temperature in winter of – 8.9 °C. Celatoblatta quinquemaculata was also found frozen under rocks in the field when the under-rock temperature was below – 3 °C, and could survive being frozen at – 5 °C for 4 days in the laboratory.
3. There was a marked decrease in LT₅₀ temperature from – 5.5 °C in April to – 7.5 °C in May. This coincides with decreasing temperatures from summer through autumn to winter, during which temperatures beneath snow-covered rocks may reach – 7.3 °C.
4. Supercooling points fluctuated during the year, with an increase from – 4.2 °C in autumn to – 3.4 °C in winter. Supercooling point was highest in spring, and changes in supercooling point do not appear to be related to changes in LT₅₀.
5. Recordings of environmental temperatures from the Rock and Pillar Range suggest that cockroaches may undergo up to twenty-three freeze–thaw cycles in the coldest month of the year, and that they may remain frozen for periods of up to 21 h. Maximum cooling rates recorded in the field (0.01 °C min^–1) were 100-fold slower than laboratory cooling rates, so survival estimates from laboratory experiments may be underestimates.     

Yield Constant for Acanthamoeba polyphaga in Batch and Continuous Culture1

ABSTRACT. A two-stage chemostat modified to accommodate the growth of adhesive organisms was used to determine the yield constant, Y, of a representative soil amoeba, Acanthamoeba polyphaga, utilizing as its prey Pseudomonas paucimobilis. The first stage consisted of a glucose-limited bacterial culture in steady state. The second stage consisted of a simplified predator-prey system, nongrowing bacteria serving as the limiting substrate for amoebae. A refined methodology to more accurately determine Y was developed, and Y for Acanthamoeba polyphaga in batch and continuous culture was determined to be 19.1%.     

Water Relations of Tropical Epiphytes: I. RELATIONSHIPS BETWEEN STOMATAL RESISTANCE, RELATIVE WATER CONTENT AND THE COMPONENTS OF WATER POTENTIAL

The water relations of five species of tropical vascular epiphytesnative to Malaysia were studied. The species were ferns: Pyrrosiaadnascens (Forst.) Ching. and Pyrrosia angustata (Sw.) Ching.;orchids: Eria velutina Lindl., Dendrobium tortile Lindl. andDendrobium crumenatum Sw. Leaf resistance as a function of leafwater potential was measured for the two ferns. The criticalwater potential at which stomata closed was found to be highin each case; –0.75 MPa and –0.5 MPa respectively.The components of water potential were estimated with the pressurechamber as functions of relative water content. For each speciescell sap was found to be dilute, pressure potential low at fullturgor, and the change in relative water content between fullturgor and wilting point small. Small values of solute potentialat full turgor were also found for the ferns and E. velutinausing a vapour pressure osmometer. Values of the bulk modulusof elasticity of the leaf tissue for each species lay withinthe range of published data. The significance of these resultsfor the epiphytic way of life is discussed. Key words: Water potential, Epiphytes, Diffusive resistance, Orchid, Fern     

Synthesis and Characterization of Nicotiana-Solanum Graft Chimeras

Intergeneric Nicotiana tabacum L./Solanum laciniatum Ait. graftchimeras were produced from decapitated grafts made betweenthese two graft compatible species. Graft unions were treatedwith or without either the auxin, p-chlorophenoxyacetic acid(p-CPA) or the cytokinin, benzylaminopurine (BAP). While BAPwas inhibitory to shoot formation, p-CPA increased the numberof adventitious shoots and raised the frequencies of shoot-forminggrafts obtained. Approximately 9% (14/151) of the shoots producedat p-CPA-treated graft unions were intergeneric chimeras. Theauxin application significantly increased levels of chimeralshoot recovery numbers thus indicating a direct auxin effecton chimeral shoot production. The types and numbers of chimerasproduced were independent of the scion/stock graft combinationemployed. All chimeras appeared to arise initially as mericlinalor sectorial chimeras, with a proportion of the former ones(5/14) stabilizing into periclinal chimeras. The morphologicalcharacteristics of these latter chimeras were compared withthose of the two parental species. The LII layer of speciesdetermined the characteristics of the vegetative and floralcomponents. However, the LI layer modified the qualitative traitsof both components. The LIII layer on the other hand alteredthe quantitative traits of the vegetative organs and the flower.This layer also determined the growth type, breeding behaviourand inflorescence type of synthesized chimeras. These organizationalfunctions of the LIII layer have not been reported previously. Chimeras, intergeneric chimera synthesis, grafting, graft chimeras, Nicotiana tabacum, Solanum aviculare, p-chlorophenoxyacetic acid, peroxidase isoenzymes     

Zearalenone production in barley

A plot of barley cv. Golden Promise was sprayed with an isolate of Fusarium culmorum known to produce zearalenone, an oestrogenic toxin. The grain was harvested and stored under conditions that were known to induce toxin production in sterilized grain inoculated with the same strain. Toxin was not found in the harvested grain but appeared 20 wk after storage. A plot of unsprayed barley was harvested at the same time as the sprayed plot. F. culmorum was isolated from the grain at the time of harvesting but there was no toxin detectable. This appeared at the same time as toxin in the sprayed plot. Higher concentrations of zearalenone were produced in the control suggesting that the F. culmorum isolated was either a different strain from that used to inoculate the sprayed plot or that the microbial flora of the grain affected toxin production.