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POSTEMBRYONIC development in plants is achieved by apical meristems. Surgical studies and clonal analysis have revealed indirectly that cells in shoot meristems have no predictable destiny and that position is likely to play a role in the acquisition of cell identity. In contrast to animal systems, there has been no direct evidence for inductive signalling in plants until now. Here we present evidence for such signalling using laser ablation of cells in the root meristem of Arabidopsis thaliana. Although these cells show rigid clonal relationships, we now demonstrate that it is positional control that is most important in the determination of cell fate. Positional signals can be perpetuated from more mature to initial cells to guide the pattern of meristem cell differentiation. This offers an alternative to the general opinion that meristems are the source of patterning information.

As part of a larger study designed to characterize the early developmental stages of the Hormel-Hanford strain miniature pig, the brain, kidney, liver, pancreas, and spleen from male animals were examined for changes in RNA, DNA, and protein contents from 1 to 196 d after birth. Distinct patterns were found for changes with age in macromolecular levels. Protein levels increased from d 1 to 56 in all organs except spleen, in which little change was noted. Gel electrophoresis showed little qualitative change in the liver protein profile during this period. A fat-free, non-nucleic acid, protein-containing fraction, insoluble in hot alkali, appeared in the brain after approximately 1 wk following birth. DNA concentrations decreased markedly from d 1 to d 196 for brain, kidney, and spleen but decreased more gradually for liver and pancreas. RNA levels declined slightly or remained the same in all organs except pancreas, where a large increase occurred from d 1 to weaning (56 d). Growth proceeded in all organs by increases in cell number (hyperplasia), as evidenced by increases in total (level or concentration X organ weight) DNA, or by hypertrophy, as evidenced by increases in the ratio of protein to DNA or by a combination of both processes. Hypertrophic growth was attained by d 56 and continued to sexual maturity in all organs except spleen. Hyperplastic growth continued to sexual maturity in all organs except brain.

It has previously been shown that the organ-specific expression of two members of the ribulose-1,5-bisphosphate carboxylase/oxygenase small subunit (rbcS) gene family is post-transcriptionally regulated in Lemna gibba. While both small subunit genes encoding SSU1 and SSU5B were transcribed at comparable levels in root and frond nuclei, SSU1 mRNA accumulated to high levels in both roots and fronds in contrast to SSU5B mRNA, which was of very low abundance in the roots compared with the fronds In this study, we have used two approaches to pinpoint the step(s) at which SSU1 and SSU5B mRNAs are differentially accumulated in these organs In the first approach, total nuclear steady state mRNA was isolated from roots and fronds, and the amount of each transcript was measured by RNase protection assays and compared with the transcription rates in isolated nuclei In the second approach, cordycepin was used to inhibit mRNA synthesis in Lemna fronds or roots, and the rate of decay of each mRNA was measured by RNA gel blot analysis or RNase protection assays Our findings indicate that the differential accumulation of SSU1 and SSU5B mRNAs in the fronds versus the roots is determined primarily in the nuclear compartment In addition, SSU1 was found to have a longer half-life in total steady state mRNA than SSU5B had in both organs This feature probably accounts for SSU1 being the predominantly expressed family member

The determination of the minimum alveolar concentration (MAC) of any inhalation anaesthetic requires repeated application of the stimulus. The investigation of the influence of body temperature on MAC in the same animal, requires even more applications of the stimulus. The use of what is commonly known as a "supramaximal stimulus", beyond which there is no increase in MAC with any further increase in stimulus intensity, is generally held to provide for the reproducibility of MAC. However, there are many conflicting reports with regard to the MAC values obtained using "supramaximal stimuli" and with the interpretation of results. | In this study the unreliability of the "supramaximal stimulus", in the form of tail clamping using a haemostat for the determination of MAC of halothane in the rabbit, was established. The use of this technique was demonstrated, both grossly and histologically, to cause severe trauma and lacerations that may have altered the sensitivity of the sensory mechanisms as indicated by the great variability in the values of MAC obtained on subsequent determinations in the same animal. Also, the technique appeared to disregard modern physiological concepts on receptor thresholds, inflammation and hyperalgesia. | Therefore, it was decided to explore more reliable techniques of stimulation. Controlled mechanical and heat stimulators were devised and used for the determination of MAC of halothane in the rabbit as the body temperature was manipulated to test the effect of environmental heating or cooling on MAC. | The mechanical stimulator is a form of pincer driven by compressed air, and is operated from a control panel with a manual trigger. It is capable of delivering a precise stimulus at a preselected pressure to the target site (ear pinna). The stimulus was calculated in terms of Newtons per unit surface area after calibration of the device using gram weights. The heat stimulator was designed to deliver a controlled, preset focal heat stimulus from a heat lamp for a preselected duration The device is V operated through a system of electronic circuits controlling the temperature and time. With both stimulators, a just noxious level of stimulation was applied. | The mechanical and heat stimulators shared some common advantages over the established clamping techniques used for the determination of MAC. Firstly, both of them were shown to be capable of delivering precise stimuli in terms of amount, duration and rate of application. The control of such components of the stimulus is essential for the reproducibility and interpretation of results, particularly in the ever growing field of comparative studies. Secondly, the stimulus applied by both stimulators was recordable. This allows for the calculation and the calibration of the applied stimulus and, together with the electronically measured and recorded movement response, it was also possible to calculate the response time. | At normothermia, the MAC values of halothane determined in the rabbit usingnondestructive stimuli from either stimulator were found to be consistent and reproducible. Hyperthermia (rectal temperature of 40.6 °C +/- 0.3 (SD) was demonstrated to cause a significant increase in MAC of halothane (12.3% per 1°C rise in body temperature) when determined using a mechanical stimulus of 1.37 +/- 0.04 (SD) N/mm^. On the other hand, no significant difference was detected in MAC determined using a focal heat stimulus of 54.35 °C +/- 0.09 (SD) in hyperthermic rabbits (41.6 °C +/- 0.4 (SD). Hypothermia of 4 °C was shown to reduce the MAC of halothane in the rabbit by 50% (12.8% per 1 °C drop in body temperature) to a focal heat stimulus of 54.3 °C, and by 35.1% (9 % per 1 °C decrease in body temperature) to a mechanical stimulus of 1.39 - 1.41 N/mm^. By extrapolation of results, it was predicted that the "anaesthetising body temperature", at which no halothane would be required to abolish movement response to such stimuli, would be 31.0 °C and 27.7 °C for the heat and mechanical stimuli respectively. It is concluded that, normal doses of potent anaesthetics similar to halothane should probably be considerably reduced in hypothermic rabbits, which must be closely monitored for signs of overdose. | In the initial stages of this study some problems were encountered regarding the determination of MAC in hyperthermic rabbits due to the difficulty in the control of animal heating. As a result a section of this thesis was devoted to the establishment of a controlled and reliable heating and cooling protocol, with some emphasis on selected cardiopulmonary parameters and some stimulus-related responses. A body temperature of 42.0 °C appeared to represent a critical temperature in the rabbit above which the normal physiological responses are interfered with and also above that temperature, induced cooling was ineffective in reducing the body temperature. | Stimulus-related responses, other than movement, included changes in arterial blood pressure, apnoea and hyperpnoea. Such responses, particularly those of the arterial blood pressure, showed both quantitative and qualitative inconsistency. Therefore it was concluded that these responses are not reliable end points for the determination of MAC in the rabbit. On the other hand, the provoked movement of the head and or limbs, remains unchallenged as the most reliable end point for the determination of MAC.

Using the doubly labeled water method (DLW), we determined total energy expenditure (TEE) under free-living conditions in 23 rural Bolivian Aymara (males and females aged 4-65), natives of a small, high-altitude (4000-4100 m), rural agropastoral community in the Andes mountains. In the adults (18-65 y of age), mean TEEs for males and females were 11.1 +/- 1.8 MJ/24 h (range: 9.3-14.1) and 9.8 +/- 0.9 MJ/24 h (8.8-11.3). Non basal energy expenditure expressed as TEE relative to basal energy expenditure (TEE:RMR) and as the difference between TEE and RMR per unit of weight [(TEE-RMR)/wt] showed no significant sex differences. TEE:RMR in the adults (2.00 +/- 0.21) was significantly greater (P <0.05) than that of adolescents and children (1.67 +/- 0.25), but the mean (TEE-RMR)/wt values were similar in children, adolescents, and adults. Significantly high RMR:FFM values in children and adolescents, reflecting a curvilinear relation of RMR and FFM, have enlarged the differences in TEE:RMR by age groups. When compared with other DLW studies for free-living nonobese adults, the RMR of adult Aymara subjects normalized by the ratio method (RMR:FFM) and by the regression-based method (RMR adjusted with FFM as the covariate) was not significantly different from that observed in subjects living in low altitudes. As compared to FAO/WHO/UNU (1985) recommendations, activity levels were classified as heavy for the adult females and moderate-heavy for the adult males. Energy requirements for maintaining everyday tasks in the Andean people are much higher than expected from the previous studies on food consumption.