Regeneration of a Natal coastal dune forest after fire

The composition of alcoastal dune forest in the MIalazi Nature Reserve, Natal was studied three years after a fire and compared with adjacent unburnt forest. The two communities had similar plant densities but there was a marked decrease in biomass and diversity in the burnt community. Measured as density, basal area or canopy volume, Trema orientalis contributed over 70% of the regenerating burnt forest. Saplings of some forest trees were-present but those of Mimusops caffra, the dominant tree of the unburnt community, were absent from the burnt area. S. A fr. J. Bot. 1985, 51 : 453 — 459Die samestelling van ‘n kusduinwoud te Mlalazi-natuurreservaat, Natal is drie jaar na ‘n brand bestudeer en met aangrensende ongebrande woud vergelyk. Die twee gemeenskappe se plantdigtheid was dieselfde, maar daar was ‘n merkbare afname in biomassa en verskeidenheid in die gebrande gemeenskap. Gemeet as digtheid, basale oppervlakte of blaredak-volume het Trema oriental is meer as 70% van die regenererende gebrande woud bygedra. Lote van sommige woudbome was aanwesig maar die van Mimusops caffra, die dominante boom van die ongebrande gemeenskap, was afwesig in die gebrande gebied. S.-Afr. Tyciskr. Plantk. 1985, 51: 453 – 45

The effect of drying rate on viability retention of recalcitrant propagules of Avicennia marina

Recalcitrant propagules of Avicennia marina were stored under different relative humidities to achieve both rapid and slow drying. Irrespective of conditions, short-term (4–8 days) storage was accompanied by increased rates of protein synthesis and respiratory activity, the initiation of vacuolation and cell division and also by enhanced rates of germination. These data indicate that the germination process is initiated upon shedding. Storage for longer periods resulted in reduced rates of germination and ultimately, in loss of viability. However, propagules dried rapidly retained viability to a lower moisture content than those dried slowly. It is suggested that as germination changes occur during storage, the propagules become increasingly sensitive to desiccation, which might coincide with the degree of vacuolation. Rapidly dried propagules have not proceeded as far along the germination pathway and, at a given moisture content, are not as desiccation sensitive as those dried slowly. Thus viability loss is dependent upon rates of drying rather than on absolute moisture content or storage time, considered independently. S. Air. J. Bot. 1985, 51: 432–438Weerspannige propagule van Avicennia marina is teen verskillende relatiewe vogtigheidswaardes geberg om vinnige sowel as stadige uitdroging teweeg te bring. Ongeag omstandighede, is korttermyn-berging (4–8 dae) gekenmerk deur ‘n verhoogde tempo van proteïensintese en respiratoriese aktiwiteit, aanvang van selholtevorming en seldeling, asook ‘n verhoogde ont-kiemingstempo. Hierdie gegewens dui daarop dat die proses van ontkieming ingelei word deur propaguulverlies. Berging vir langer tydperke het gelei tot verlaagde ontkiemingstempo, en uiteindelik tot verminderde kiemkrag. Propagule wat vinnig uitgedroog is, het egter hul kiemkrag tot op ‘n laer voggehalte behou as die wat stadig uitgedroog is. Daar word voorgestel dat die propagule toenemend sensitief word vir uitdroging, soos ontkiemingsveranderinge gedurende berging plaasvind, en dat dit moontlik saamval met die graad van selholtevorming. Vinnig-gedroogde propagule het nog nie so ver gevorder tot ontkieming nie, en by ‘n spesifieke voggehalte is hulle nie so droogte-sensitief soos die wat stadig uitgedroog het nie. Verlies aan kiemkragtigheid is gevolglik eerder afhanklik van uitdro-gingstempo as van absolute voggehalte of bergingstyd. S.-Afr. Tydskr. Plantk. 1985, 51: 432–43

ROOT-SHOOT HYDRAULIC CONDUCTANCES OF THREE Eucalyptus SPP. CLONES TO DIFFERENT WATERING REGIMES

The fast growth of Eucalyptus spp. commercially used for wood and woodproducts in the forestry industry in South Africa. On the other hand,Eucalyptus plantings, which are believed to reduce the underground watersupplies while, consume large quantities of water, perhaps the main factorlimiting forestry expansion too. South African forestry industries are concernfor improving silvicultural practices by selecting water use efficientEucalyptus clones that would not only restrict water utilization, but to beoptimum productive. Recently, three Eucalyptus spp. clones namelyEucalyptus grandis x camaldulensis (GC550), Eucalyptus grandis xurophylla (GU21O) and a pure Eucalyptus grandis (TAGI4) were introducedto study the responses to water availability. Three Eucalyptus clones ofGC550, GU210 and TAGI4, each with six replicates were randomized andgrown for 21 months in 85 I pots. Water availability of high and low as per arainfall simulation was assessed in terms of hydraulic architecture of root,shoot and whole plant hydraulic characteristics. Hydraulic conductance wasmeasured on roots and shoots using the high-pressure flow meter (HPFM).HPFM measures maximum root-shoot conductances by transient and steadystate methods. Root data were expressed per unit root dry mass (Kr/trdw) andper unit leaf areas (Kr/LA), shoot data expressed per unit shoot dry mass(KS/tsdw) and per unit leaf area (KSILA), and whole plant conductance wasexpressed per unit leaf area (KpILA). KrlLA was higher in high watered plantsthan those receiving low water, and clonal differences were observed inKr/trdw. There was no treatment effect in KSILA and KS/tsdw, but a clonal effectwas apparent. KplLA was significantly different between treatments, and wasreduced by low water in two clones of GC550 and GU210, and increased bythis in TAG 14. Reduced water availability increased root resistances e/KrILA) , except in TAG 14 where treatment had no effect. GU210 had thehighest root resistances under both treatments. Reduced water availabilityreduced biomass production, with a greater effect on roots than shoots, suchthat low watering reduced root: shoot ratios

Immunization procedure-related immunoglobulin levels in the development of antibodies against Cysticercus cellulosae

Various immunization procedures were investigated in an effort to improve the number of hybridomas producing antibodies against Cysticercus cellulosae. Ten groups of 5 BALB/c mice were subjected to different immunization procedures and were bled repeatedly over a period of 68 days. The samples of sera thus obtained were tested by enzyme linked immunosorbent assay : total immunoglobulins, lgG and IgM levels were determined. In general, total anticyst antibody titres increased during the course of immunization but in 3 groups the final titre was lower than the maximal antibody titre. Overall, immune tolerance did not appear to be a problem and longer immunization programs seemed to end with slightly higher antibody levels. So far, 4 mice from the group that exhibited the highest immunoglobulin levels have been used for hybridoma production. Out of 124 hybridomas thus obtained, only 1 secreted antibodies against Cysticercus cellulosae.The articles have been scanned in colour with a HP Scanjet 5590; 600dpi. Adobe Acrobat XI Pro was used to OCR the text and also for the merging and conversion to the final presentation PDF-format.lmchunu2014mn201

Desarrollo de la comprensin de las semillas recalcitrantes y las implicaciones para la conservacin ex situ

Recalcitrant seeds are shed at high water content, are desiccation sensitive and cannot be stored under conditions conventionally employed for desiccation-tolerant orthodox seeds. Recalcitrant seeds are metabolically active when shed, with high rates of respiration and a high degree of intracellular differentiation. Development grades gradually into germination, with no punctuating quiescent period, and many recalcitrant seeds will germinate if aintained at their shedding water content. Consequently, storage in the hydrated condition is strictly a short-term option only. Although recalcitrant seeds are desiccation sensitive, if excised embryonic axes are dried very rapidly they will survive to lower water contents than those dried slowly. When axes are dried they are initially subject to aqueous-based oxidative degradative processes. Axes dried slowly are exposed to these conditions for an extended period of time, accumulate considerable damage and die at high water contents. Rapidly dried axes accumulate less damage over a shorter period and so survive to lower water contents. The response of excised axes to rapid drying opens up the possibility of cryo-storage. Partial drying reduces the chances of ice formation on subsequent exposure to cryogenic temperatures, and if the drying is rapid, will reduce oxidative damage. Rapid cooling can induce the remaining intracellular water to vitrify, permitting cryo-storage without damaging ice crystal formation. However, because of the highly variable physiology of recalcitrant seeds and axes, detailed protocols have to be established on an individual species basis, guided by these concepts.Key words: Cryopreservation, damage, desiccation, recalcitrant seeds, storageLas semillas recalcitrantes se desprenden cuando el contenido de agua es alto, son sensibles a la desecación y no se pueden almacenar en condiciones convencionalmente empleadas para las semillas ortodoxas-tolerantes a la desecación. Las semillas recalcitrantes son metabólicamente activas cuando se desprenden, tienen altas tasas de respiración y un alto grado de diferenciación intracelular. Si se mantiene elevado el contenido de agua de las semillas, hay un desarrollo gradual en la germinación y no se interrumpe la dormancia, muchas semillas recalcitrantes germinarán. En consecuencia, el almacenamiento en el estado hidratado es estrictamente una opción a corto plazo. Aunque las semillas recalcitrantes son sensibles a la desecación, si los ejes embrionarios se separan y se secan muy rápidamente van a sobrevivir a contenidos de agua bajos más que si  se secan lentamente. Cuando los ejes se secan se someten inicialmente a un proceso de degradación oxidativa de base acuosa. Los ejes que se secan lentamente están expuestos a estas condiciones durante un período prolongado de tiempo, se acumulan daños considerables y mueren en presencia de altos contenidos de agua. Los ejes que se secan rápidamente acumulan menos daño en un período de tiempo más corto y así pueden sobrevivir a bajos contenidos de agua. La respuesta de los ejes embrionarios al secado rápido abre la posibilidad de crio-almacenamiento. El secado parcial reduce las posibilidades de formación de hielo en la posterior exposición a temperaturas criogénicas, y si el secado es rápido, reducirá el daño oxidativo. El enfriamiento rápido puede inducir el agua intracelular restante para vitrificar, lo que permite el crio-almacenamiento sin dañar la formación de cristales de hielo. Sin embargo, debido a la fisiología altamente variable de las semillas recalcitrantes y los ejes, no se han establecido protocolos detalladossobre la base de especies individuales, guiados por estos conceptos.Palabras clave: almacenamiento, crioconservación, daño, desecación, semillas recalcitrante