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Biomedical subjects

J A Morgan

Publications and source records attributed to J A Morgan.

At least 91 records · Page 5Linked to original sources
PubMed1986

The Effects of N Nutrition on the Water Relations and Gas Exchange Characteristics of Wheat (Triticum aestivum L.).

The purpose of this study was to characterize leaf photosynthetic and stomatal responses of wheat (Triticum aestivum L.) plants grown under two N-nutritional regimes. High- and low-N regimes were imposed on growth-chamber-grown plants by fertilizing with nutrient solutions containing 12 or 1 millimolar nitrogen, respectively. Gas-exchange measurements indicated not only greater photosynthetic capacity of high-N plants under well-watered conditions, but also a greater sensitivity of CO(2) exchange rate and leaf conductance to CO(2) and leaf water potential compared to low-N plants. Increased sensitivity of high-N plants was associated with greater tissue elasticity, lower values of leaf osmotic pressure and greater aboveground biomass. These N-nutritional-related changes resulted in greater desiccation (lowered relative water content) of high-N plants as leaf water potential fell, and were implicated as being important in causing greater sensitivity of high-N leaf gas exchange to reductions in water potential. Water use efficiency of leaves, calculated as CO(2) exchange rate/transpiration, increased from 9.1 to 13 millimoles per mole and 7.9 to 9.1 millimoles per mole for high- and low-N plants as water became limiting. Stomatal oscillations were commonly observed in the low-N treatment at low leaf water potentials and ambient CO(2) concentrations, but disappeared as CO(2) was lowered and stomata opened.

Journal Article↗
PubMed1986

Cell and molecular analysis of long-term sensitization in Aplysia.

We have found that one cellular locus for the storage of the memory underlying short-term sensitization of the gill and siphon withdrawal reflex in Aplysia is the set of monosynaptic connections between the siphon sensory cells and the gill and siphon motor neurons. These connections also participate in the storage of memory underlying long-term sensitization. In animals that have undergone long-term sensitization, the amplitudes of the monosynaptic connections are significantly larger (2.2x) than the ones in control animals. To study the mechanisms of onset and retention of long-term synaptic facilitation that underly long-term sensitization and the role of protein synthesis in long-term memory, we have developed two types of reduced preparations: the intact reflex isolated from the remainder of the animal, and a dissociated cell culture system in which the monosynaptic component (sensory neurons and motor neurons) of the neuronal circuit mediating the withdrawal reflex is reconstituted. We found that protein synthesis inhibitors, such as anisomycin or emetine, and RNA synthesis inhibitors, such as actinomycin D or alpha-amanitin, blocked long-term facilitation without interfering with short-term facilitation. These results suggest that the acquisition of long-term memory may require the expression of genes and the synthesis of proteins not needed for short-term memory.

Amanitins↗
PubMed1984

Primary cardiac haemangiomas. A report of 2 cases.

Primary heart tumours are extremely rare. Over a period of 25 years 22 primary cardiac tumours were diagnosed clinically or at autopsy at Groote Schuur Hospital. Fourteen patients with myxomas, 1 with lymphocytic lymphoma and 2 with haemangiomas underwent surgery. A further 4 myxomas and 1 histiocytoma were found at autopsy. In both the cases of haemangioma the diagnosis of a vascular tumour was made before surgery. One tumour had infiltrated the lateral wall of the left ventricle and was unresectable; only a biopsy specimen was taken. The patient, however, remains well some 6 years later. In the second patient the haemangioma was situated in the outflow tract of the right ventricle and was successfully excised. The clinical history, pathological features and management of both cases are presented.

Child, Preschool↗
PubMed1984

Interaction of water supply and N in wheat.

The purpose of this study was to investigate effects of N nutrition and water stress on stomatal behavior and CO(2) exchange rate in wheat (Triticum aestivum L. cv Olaf). Wheat plants were grown hydroponically with high (100 milligrams per liter) and low (10 milligrams per liter) N. When plants were 38 days old, a 24-day water stress cycle was begun. A gradual increase in nutrient solution osmotic pressure from 0.03 to 1.95 mega Pascals was achieved by incremental additions of PEG-6,000. Plants in both N treatments adjusted osmotically, although leaf water potential was consistently lower and relative water content greater for low N plants in the first half of the stress cycle. Leaf conductance of high N plants appeared greater than that of low N plants at high water potentials, but showed greater sensitivity to reductions in water potential as indicated by earlier stomatal closure during the stress cycle. The apparent greater stomatal sensitivity of high N plants was associated with a curvilinear relationship between leaf conductance and leaf water potential; low N plants exhibited more of a threshold response. Trends in [CO(2)](INT) throughout the stress cycle indicated nonstomatal effects of water stress on CO(2) exchange rate were greater in high N plants. Although estimates of [CO(2)](INT) were generally lower in high N plants, they were relatively insensitive to leaf water potential-induced changes in leaf conductance. In contrast, [CO(2)](INT) of low N plants dropped concomitantly with leaf conductance at low leaf water potentials. Oxygen response of CO(2) exchange rate for both treatments was affected less by reductions in water potential than was CO(2) exchange rate at 2.5% O(2), suggesting that CO(2) assimilation capacity of the leaves was affected more by reductions in leaf water potential than were processes related to photorespiration.

Journal Article↗
PubMed1980

Photosynthesis in Grass Species Differing in Carbon Dioxide Fixation Pathways: III. OXYGEN RESPONSE AND ENZYME ACTIVITIES OF SPECIES IN THE LAXA GROUP OF PANICUM.

Measurements of CO(2) exchange at varying O(2) concentrations in seven grass species of the Laxa group of Panicum and activities of five photosynthetic enzymes were compared to values obtained for these characters in a cool season C(3) grass, tall fescue (Festuca arundinacea Schreb.) and a C(4) grass, P. maximum Jacq. Plants were divided into three groups on the basis of the inhibition of apparent photosynthesis by 21% O(2.) Rates of apparent photosynthesis in P. prionitis Griseb. and P. maximum were virtually unaffected by changes in O(2) concentration. In another group consisting of P. hylaeicum Mez., P. rivulare Trin., P. laxum Sw., and tall fescue apparent photosynthesis was inhibited by 28.2 to 36.0% at 21% O(2.) An intermediate inhibition of 20.6 to 23.3% at 21% O(2) was exhibited by P. milioides Nees ex Trin., P. schenckii Hack., and P. decipiens Nees ex Trin. The CO(2) compensation concentration for P. prionitis and P. maximum was low (</=6 microliters per liter CO(2) at 21% O(2)) and affected little by O(2), whereas values for P. hylaeicum, P. rivulare, P. laxum, and tall fescue were much greater, and increased almost linearly from 2 to 48% O(2.) Values for P. milioides, P. schenckii, and P. decipiens were intermediate to the other two groups. The effect of O(2) on total leaf conductance to CO(2) was similar to the C(3) grasses and the intermediate Panicums. However, estimates of photorespiration in the intermediate species were low and changed little with O(2) in comparison to estimates for the C(3) species which were higher and increased greatly with increased O(2.)Activities of phosphoenolpyruvate carboxylase were greatest in P. maximum and P. prionitis and one-fourth or less in the remaining species. Activity of ribulose bisphosphate carboxylase was 548 micromoles per mg chlorophyll per hour in tall fescue; activity in the remaining species was approximately one-fourth or less of that in tall fescue, with the exception of P. rivulare, in which it was 440 micromoles per milligram chlorphyll per hour. High activities of two C(4) decarboxylating enzymes, phosphoenolpyruvate carboxykinase and NADP-malic enzyme, were observed in P. maximum (1,988 micromoles per milligram chlorophyll per hour) and P. prionitis (125 micromoles per milligram chlorophyll per hour), respectively. Only minimal activities of decarboxylating enzymes were detected in the remaining species.

Journal Article↗
PubMed1980

Photosynthesis of Grass Species Differing in Carbon Dioxide Fixation Pathways : VI. DIFFERENTIAL EFFECTS OF TEMPERATURE AND LIGHT INTENSITY ON PHOTORESPIRATION IN C(3), C(4), AND INTERMEDIATE SPECIES.

The effects of temperature and photosynthetically active radiation levels on photorespiration were investigated in Panicum milioides Nees ex Trin. and Panicum schenckii Hack., species known to have low photorespiration rates and other characteristics intermediate between C(3) and C(4) species. Comparisons were made with the C(3) grass species tall fescue (Festuca arundinacea Schreb.). An increase in temperature from 20 to 35 C raised photorespiration from 7.3 to 10.2 milligrams per square decimeter per hour in tall fescue, but the increase in P. schenckii was less than 1 milligram per square decimeter per hour. Increases in temperature caused much less change in CO(2) compensation concentration in P. milioides and P. schenckii than in tall fescue, values of 160 microliters per liter being obtained in tall fescue at 40 C compared to about 40 microliters per liter for P. milioides and P. schenckii. Photorespiration in P. schenckii increased by only about 1 milligram CO(2) per square decimeter per hour as the photosynthetically active radiation level was raised from 100 to 2,000 microEinsteins per square meter per second. Loss of CO(2) into CO(2)-free air actually decreased from 2.2 to 1.0 milligrams per square decimeter per hour as the radiation level was raised from 100 to 1,100 microEinsteins per square meter per second but tended to rise again at 2,000 microEinsteins per square meter per second. In contrast, photorespiration in tall fescue tripled with radiation level over the same range, reaching a maximum value of 7.2 milligrams per square decimeter per hour as determined by extrapolation of the CO(2) response curves to zero CO(2). The CO(2) compensation concentration in tall fescue was nearly insensitive to photosynthetically active radiation above 140 microEinsteins per square meter per second but, in P. milioides and P. schenckii, it decreased from values of 69 and 62 microliters per liter, respectively, to values of 21 and 16 as the radiation level was increased from 50 to 1075 microEinsteins per square meter per second. Interpolation of CO(2)-response curves showed that an increase in photosynthetically active radiation level from 100 to 2,000 microEinsteins per square meter per second reduced the CO(2) compensation value of P. schenckii from 38 to 19 microliters per liter. Data from these experiments indicate reduced photorespiration or a CO(2)-recycling mechanism in P. milioides and P. schenckii which causes apparent photorespiration to be nearly insensitive to temperature in the 20 to 35 C range and to decrease at high radiation intensities.

Journal Article↗
PubMed1979

Photosynthesis in Grass Species Differing in Carbon Dioxide Fixation Pathways: II. A Search for Species with Intermediate Gas Exchange and Anatomical Characteristics.

Thirty-three grass species were examined in two experiments in an attempt to locate plants with photosynthetic responses to O(2), CO(2) compensation concentrations, and leaf anatomy intermediate to those of C(3) and C(4) species. Species examined included seven from the Laxa group in the Panicum genus, one of which, P. milioides Nees ex Trin., has been reported earlier to have intermediate characteristics. The species with O(2)-sensitive photosynthesis typical of C(3) plants showed more than 37% increase in apparent photosynthesis at 2% O(2) compared to 21% O(2) at 25 C and 335 microliters per liter CO(2), whereas in Panicum milioides, P. schenckii Hack., and P. decipiens Nees ex Trin., members of the Laxa group of Panicum, increases ranged from 25 to 30%. The remainder of the species did not respond to O(2). Species with O(2) responses characteristic of C(3) plants exhibited CO(2) compensation concentrations of 44 microliters per liter or higher at 21% O(2) and 25 to 27.5 C and species characterized as O(2)-insensitive had values of microliters per liter or less. The CO(2) compensation concentration (capital GHE, Cyrillic) values of P. milioides, P. schenckii, and P. decipiens ranged from 10.3 to 23.3 microliters per liter. Other species of the Laxa group of Panicum exhibited O(2) response and capital GHE, Cyrillic values of either C(3) (P. laxum Sw., P. hylaeicum Mez., and P. rivulare Trin.) or C(4) (P. prionitis Griseb.) plants. Leaves of species with O(2) response and CO(2) compensation values typical of C(3) plants had poorly developed or nearly empty bundle sheath cells, and much larger distances and mesophyll cell numbers between veins than did the O(2)-insensitive ones. Vein spacings in P. milioides, P. schenckii, and P. decipiens ranged from 0.18 to 0.28 millimeter and mesophyll cell number between veins from 5.2 to 7.8. While these vein spacings are closer than those of most C(3) grasses, two O(2)-sensitive species of Dactylis had vein spacings similar to these Panicums and veins in Glyceria striata, another O(2)-sensitive plant, were separated by only four mesophyll cells and 0.12 millimeter. Bundle sheath cells of the three intermediate Panicums contained greater quantities of organelles than are typical for C(3) grasses.

Journal Article↗
PubMed1978

Charcot-Marie-Tooth disease with Leber optic atrophy.

A family is described in which visual failure was associated with hypertrophic Charcot-Marie-Tooth disease. The diagnosis of Charcot-Marie-Tooth disease was confirmed by electrophysiologic studies and by quantitative histologic studies of sural nerve biopsies. The clinical features and mode of inheritance of the visual failure were those of Leber optic atrophy. The two conditions were inherited independently.

Adolescent↗
PubMed1977

Electrophysiological studies in familial spastic paraplegia.

Motor and sensory conduction studies have been performed in 10 patients from three families with uncomplicated familial spastic paraplegia whose ages ranged from 4 to 41 years. In all cases the values fell within the control range. The findings may be contrasted with those in Friedreich's ataxia and some other spinocerebellar degenerations in which peripheral nerve abnormalities are present.

Action Potentials↗
PubMed1976

Electrophysiological and pathological studies in spinocerebellar degenerations.

Electrophysiological and pathological studies have been performed on the peripheral nerves of patients with spinocerebellar degenerations. In Friedreich's ataxia there is impairment of sensory conduction and mild slowing of motor conduction which may be correlated with loss of large diameter fibres in the sural nerve. The abnormalities in Friedreich's ataxia are present early, in the first decade. In hereditary spastic paraparesis the nerve conduction studies and sural nerve biopsy are normal. In the other spinocerebellar degeneration and a mild loss of myelinated fibres in the sural nerve. However the abnormalities differ from those seen in Friedreich's ataxia.

Cerebellar Diseases↗
PubMed1975

A family with Charcot-Marie-Tooth disease and Leber's optic atrophy.

A family has been studied in which members of 4 generations were affected by the hypertrophic type of Charcot-Marie-Tooth disease. The diagnosis was confirmed by electrophysiological studies and by sural nerve biopsy. 10 members of the family, 8 males and 2 females, developed optic atrophy of acute onset with progression over a period of two to six months. The history of visual failure, its maternal inheritance, and the neuro-ophthalmological findings of optic atrophy with bilateral central scotomata were typical of Leber's optic atrophy. 2 members of the family suffered from both Charcot-Marie-Tooth disease and Leber's optic atrophy. There have been a few previous reports of optic atrophy associated with Charcot-Marie-Tooth disease, and in the present family both conditions appeared to have been inherited independently.

Adolescent↗