No description available.

No description available.

No description available.

The developmental potential of mammalian oocytes cryopreserved with procedures similar to those used for embryos has been limited, inasmuch as oocytes differ from embryos in advanced stages of development, both physiologically and morphologically. The objective of this work was to elucidate the precise nature of freeze-thaw damage with the expectation that identification of specific targets will enable devising optimal procedures for cryopreservation of bovine oocytes to prevent specific damage and minimize the loss of developmental capacity. / In the first series of experiments, bovine oocytes were vitrified (V-oocytes) or frozen slowly (S-oocytes) at the germinal vesicle (GV) stage or after maturation in vitro (IVM). Survival was assessed morphologically and also by in vitro fertilization (IVF) and culture (IVC). Morphological integrity and developmental capacity were greater in S-oocytes than in V-oocytes (P $<$ 0.05). Transfer of four embryos (2 morulae and 2 blastocysts) derived from post-IVM S-oocytes into a recipient heifer resulted in the birth of twin calves. / In the second series of experiments, oocytes (GV and IVM) were exposed to a cryoprotectant solution (DAP213: 2M DMSO, 1M acetamide, 3M propanediol) for 1.5 or 5 min and viability assessed by IVM-IVF-IVC. Oocytes were also examined by transmission electron microscopy (TEM) before (control) or after exposure to the cryoprotectant. DAP213 induced profound premature cortical granule (CG) release and vesiculation. These changes were less pronounced in oocytes exposed to DAP213 only after IVM. The results suggest that: (1) the extrusion of CG is one of the important cytological events affected by the treatment of oocytes with DAP213; (2) GV oocytes are more sensitive to the cryoprotectant than IVM oocytes. / In the third series of experiments, GV and IVM oocytes were vitrified with DAP213. On rewarming, DAP213 was removed by a one- or three-step dilution procedure and survival assessed by development after IVM-IVF-IVC. Morphology was assessed by TEM study immediately following DAP213 removal. Both assessments indicated that: (1) IVM oocytes are more tolerant to vitrification than are GV oocytes; (2) the three-step dilution is less damaging than the one-step procedure; (3) changes in the zona pellucida (loss of plasticity) of IVM oocytes following vitrification may result from the premature release of cortical granules.

Dietary fatty acid (FA) composition and energy restriction (ER) independently affect serum leptin levels; however it is not known whether this correlates with changes in obese (ob) gene expression. Herein, we assessed whether dietary FA composition and ER influence white adipose tissue (WAT) ob mRNA by Northern analysis. Animals consumed diets containing tallow (BT), safflower oil (SO) or fish oil (FO) ad libitum or at 60% ad libitum intakes. Serum leptin values were not different between levels of energy intake. ER decreased weight gain and WAT weights, which positively correlated with serum leptin values. WAT ob mRNA levels were in the rank order: FO > SO > BT in depots of all groups with ER showing a lower level of ob mRNA. Data show similarity in ob mRNA levels between depots with discordance in circulating leptin levels. These data suggest that energy restriction exerts greater control over leptin production than dietary fat source.

No description available.

No description available.

No description available.

vii, 252 leaves : ill., photos., tables ; 30 cm. / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / Thesis (Ph.D.1979)--University of Adelaide, Dept. of Agronomy, 1978

Although it has long been recognized that physiological acclimation of photosynthesis and respiration can occur in plants exposed to changing environmental conditions (e.g. light, temperature or stress), the extent of acclimation in different tissues (i.e. pre-existing and new foliage) however, has not received much attention until recently. Furthermore, few studies have investigated the extent of photosynthetic and respiratory acclimation under natural conditions, where air temperatures vary diurnally and seasonally. In this study, the effects of variations in temperature on respiratory CO2 loss and photosynthetic carbon assimilation were examined under both controlled and natural environments. The purpose of the investigations described in this thesis was to identify the effects acclimation would have on two key metabolic processes in plants exposed to temperature change, with emphasis also placed on the role of nutrition (nitrogen) and respiratory enzymatic characteristics on the potential for acclimation in two contrasting tree species, Pinus radiata and Populus deltoides. Controlled-environment studies (Chapter 2 and 3) established that rates of foliar respiration are sensitive to short-term changes in temperature (increasing exponentially with temperature) but in the longer-term (days to weeks), foliar respiration acclimates to temperature change. As a result, rates of dark respiration measured at any given temperature are higher in cold-acclimated and lower in warm-acclimated plants than would be predicted from an instantaneous response. Acclimation in new foliage (formed under the new temperature environment) was found to result in respiratory homeostasis (i.e. constant rates of foliar respiration following long-term changes in temperature, when respiration is measured at the prevailing growth temperature). Available evidence suggests that substantial adjustments in foliar respiration tend to be developmentally dependent. This may in part explain why respiratory homeostasis was only observed in new but not in pre-existing tissues. Step changes in temperature (cold and warm transfers) resulted in significant changes in photosynthetic capacity. However, in stark contrast to the findings of respiration, there was little evidence for photosynthetic acclimation to temperature change. The results obtained from field studies (Chapter 4) show that in the long-term over a full year, dark respiration rates in both tree species were insensitive to temperature but photosynthesis retained its sensitivity, increasing with increasing temperature. Respiration in both species showed a significant downregulation during spring and summer and increases in respiratory capacity were observed in autumn and winter. Thermal acclimation of respiration was associated with a change in the concentration of soluble sugars. Hence, acclimation of dark respiration under a naturally changing environment is characterized by changes in the temperature sensitivity and apparent capacity of the respiratory apparatus. The results from controlled and natural-environment studies were used to drive a leaflevel model (which accounted for dark respiratory acclimation) with the aim of forecasting the overall impact of responses of photosynthesis and respiration in the long term (Chapter 5). Modellers utilise the temperature responses of photosynthesis and respiration to parameterize carbon exchange models but often ignore acclimation and use only instantaneous responses to drive such models. The studies here have shown that this can result in erroneous estimates of carbon exchange as strong respiratory acclimation occurs over longer periods of temperature change. For example, it was found here that the failure to factor for dark respiratory acclimation resulted in the underestimation of carbon losses by foliar respiration during cooler months and an overestimation during warmer months - such discrepancies are likely to have an important impact on determinations of the carbon economy of forests and ecosystems. The overall results substantiate the conclusion that understanding the effect of variations in temperature on rates of carbon loss by plant respiration is a prerequisite for predicting estimates of atmospheric CO2 release in a changing global environment. It has been shown here that within a moderate range of temperatures, rate of carbon uptake by photosynthesis exceeds the rate of carbon loss by plant respiration in response to warming as a result of strong respiratory acclimation to temperature change. This has strong implications for models which fail to account for acclimation of respiration. At present, respiration is assumed to increase with increasing temperatures. This erroneous assumption supports conclusions linking warming to the reinforcement of the greenhouse effect.