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PubMed1999

Protein kinase C activators inhibit the visual cascade in Limulus ventral photoreceptors at an early stage.

The phosphoinositide cascade mediates visual transduction in invertebrate photoreceptors. Phospholipase C (PLC) catalyzes the hydrolysis of phosphatidylinositol bisphosphate, producing inositol trisphosphate (InsP(3)) and diacylglycerol (DAG). Protein kinase C (PKC) is a major target of DAG in many cell types. We have used PKC activators to investigate the function of the kinase in the phototransduction cascade in Limulus polyphemus ventral photoreceptors. Extracellular application of (-)-indolactam V (0. 03-30 microM) or phorbol-12,13-dibutyrate (10 microM) reversibly reduced the sensitivity of the electrical response of the photoreceptors to light by up to 1000-fold. The inert stereoisomer (+)-indolactam V and 4alpha-phorbol had no effect. The effect of (-)-indolactam V was antagonized by the PKC inhibitors bisindolylmaleimide I and Gö 6976. Coapplication of bisindolylmaleimide V, used as a negative control compound for PKC inhibition, did not reduce the effectiveness of (-)-indolactam V. These findings are consistent with (-)-indolactam V activating PKC and desensitizing the light response. Furthermore, our pharmacological results indicate that PKC activation does not appear to play a role in light adaptation. We localized the position of the target of PKC in the visual cascade. We chemically excited the cascade at various stages to determine the kinase's target. PKC activation by (-)-indolactam V decreased the light-induced elevation of intracellular calcium but had no effect on the photoreceptor's excitatory response to intracellular injection of InsP(3). However, the PKC activator greatly reduced the excitation caused by GTP-gamma-S injection. We propose that PKC inhibits the visual transduction cascade at the G-protein and/or PLC stage.

Adaptation, Ocular↗
PubMed1985

Localization of S-antigen under various conditions of light or dark adaptation in the rabbit.

The localization of the S-antigen was studied by electron microscopy in the rabbit eye, under three conditions of adaptation: A) 24-hour dark adaptation, B) 24-hour dark adaptation and 1.5-hour light adaptation and C) light adaptation for 30 hours. The Fab' fraction of the IgG of rabbit against the swine S-antigen was labeled with horseradish peroxidase (HRP) and was used as the marking antibody. In Group A, the HRP reaction products indicating the S-antigen were found mainly in the disk and plasma membranes of the outer segments of the photoreceptor cells. The reaction products were also found diffusely in the cytoplasm of the inner segment with the exception of the mitochondria and nucleus. In Group B, the phagosomes were found surrounded by the multilayered microvilli of the retinal pigment epithelial (RPE) cells; the reaction products were scarcely found in the phagosomes but were seen in the microvilli. Some weak reaction products were also encountered in the cytoplasm of the RPE cells. In Group C, after 30-hour light adaptation, many phagosomes were found but they contained almost no reaction products. However, the microvilli of the RPE cells surrounding the phagosomes showed a fair amount of the reaction products. The cytoplasm of the RPE cells contained abundant reaction products, particularly in the area of the basal infoldings. The reaction products were also seen in the Bruch's membrane and the endothelial cells of the choriocapillaris. It was thought that the S-antigen is taken up by the RPE during phagocytosis of the shed outer segments and is transported to the choriocapillaris.

Adaptation, Physiological↗
PubMed1993

The evolution of chemoreception in squamate reptiles: a phylogenetic approach.

Recent advances in the field of squamate reptile chemoreception have been paralleled by the growth and preeminence of cladistics in the field of systematics, but for the most part, workers in the former have failed to incorporate the conceptual and informational advances of the latter. In this paper, I attempt a preliminary rapprochement by combining the methods of phylogenetic systematics and current hypotheses of squamate relationships with an overview of squamate chemosensory biology. This purely phylogenetic approach leads to a number of falsifiable generalizations about the evolution of chemoreception in squamates: 1) Evolution of this system is conservative rather than plastic, reflecting to a large extent suprafamilial attributes rather than adaptation to local conditions; 2) Anguimorphs are highly chemosensory and teiids show convergence with this group; 3) Tongue-flicking, a bifurcated tongue tip, a vomeronasal (VNO) mushroom body, and a complete circular muscle system in the tongue are a correlated character complex associated with the attainment, in squamates, of a direct VNO-oral connection and the loss of a VNO-nasal connection; 4) There is little support for a visual-chemosensory dichotomy within Squamata; 5) Gekkotans are allied with Autarchoglossa, both phylogenetically and in terms of chemosensory biology; 6) Iguania are highly variable in chemosensory development; iguanids represent the primitive iguanian condition, while agamids and chamaeleonids have secondarily reduced or lost their chemosensory abilities; 7) Apparent contradictions in chemosensory behavior among iguanids probably represent intrafamilial divergence; 8) Ecological correlates within Iguanidae and other taxa might be spurious, resulting from historical factors unrelated to the adaptations in question; 9) The mechanical demands of lingual food prehension have constrained chemosensory evolution in Iguania; chemosensory evolution within Scleroglossa was permitted by the liberation of the tongue from this ancestral role.

Amphibians↗
PubMed1989

Multiple types of neuropeptide Y-containing neurons in primate neocortex.

The avidin-biotin-peroxidase method was used at the light and electron microscopic levels to analyze neuropeptide Y (NPY)-containing neurons in the neocortex of six adult macaque monkeys. Regions studied included various sensory, motor, limbic, and association areas, designated as 17, 18, 7, 22, 3, 4, 6, 24, and 9 by Brodmann (Beiträge zur Histologischen Lokalisation der Grosshirnrinde. Leipzig: Barth, '06). Several types of NPY-containing neurons can be distinguished by their laminar location, by the size of their perikarya, and by the size, shape, and pattern of ramification of their processes: 1) layer I small local circuit neurons; 2) layer II granule cells; 3) aspiny stellate cells located in layers II-III and V-VI, with long, slender dendrites; 4) sparsely spiny stellate cells; 5) aspiny stellate cells with long, horizontally oriented dendrites, whose cell body is situated in layer VI; 6) Martinotti cells in areas 9, 7, and 24; and 7) multipolar neurons situated in the white matter subjacent to the cortical gray. The possibility of additional neuronal types containing NPY is suggested by labeled densely spinous dendrites in area 6 and recurving axons and axonal loops in the supragranular layers in areas 7 and 9. No NPY-containing neurons were found in layer IV of any area, except layers IVA and B of the visual cortex. Likewise, nonneuronal elements were not labeled. The regional differences in the distribution of some NPY-containing neuron types may reflect adaptations of local neuronal circuits for specialized functions.

Animals↗
PubMed2004

Development and validation of an Arabic rheumatoid hand disability scale.

PURPOSE: To develop a rheumatoid hand disability scale in the Arabic language adapted for local sociocultural specificities and to test its psychometric properties. METHODS: The choice of hand activities was based on several published indices. The selected items were translated by the forward and backward translation procedures, several modifications were made, and after some questions were added, a provisional scale was obtained. In- and outpatients with rheumatoid arthritis (RA) according to the ACR criteria were chosen to answer the provisional scale and to assess the final scale. Impairment outcome measures (pain as measured on a visual analogue scale, morning stiffness, hand swelling, tenderness), and assessment of disability (on Lee's and Revel's functional indices) were also recorded. The intraclass correlation coefficient and the Bland and Altman methods were used to assess reliability. Construct (convergent and divergent) validity was investigated with use of Spearman's rank correlation, and a factor analysis was performed. RESULTS: The provisional scale had 21 questions. The adaptation process left 10 questions about hand activity, with four levels of answers. Eighty patients with RA were recruited for the validation of the final scale. The intra- and interrater reliabilities of the scale were 0.96 and 0.94, respectively. Analysis by the Bland and Altman method showed no systematic trend. The scale had good construct validity, with expected convergence with Lee's functional index (r(s)=0.79) and Revel's functional index (r(s)=0.81) and divergence with age (r(s)=0.05), morning stiffness (r(s)=0.40), pain (r(s)=0.32), and tenderness (r(s)= -0.48). The factorial structure of the scale was satisfying, with two factors explaining 73% of the variance. CONCLUSION: We developed an Arabic index that assesses hand disability due to RA and suits Tunisian people. Further studies are needed to confirm the validity of the scale in other Arabic countries.

Adolescent↗
PubMed2002

Temperature resistant Nocardia biovarieties in Tucumán, Argentina?

Eighty-six regional strains of the pathogenic Nocardia species isolated from soil and human mycetoma were tested for their response to different incubation temperatures and for their tolerance to different temperatures. The aim was to assess whether growth temperature and tolerance to elevated temperatures are valuable criteria for the differentiation of pathogenic species of local strains based on the results obtained from a large number of strains. The results showed that 75.34% of all N. brasiliensis isolates from both sources grew at a temperature higher than 37 degrees C. 20% of the mycetoma strains and 11.32% of those from soil grew at 45 degrees C. 98.1% of N. brasiliensis from soil and 55.0% of the mycetoma strains tolerated 50 degrees C for 8 h and many isolates from both sources endured this temperature for an even longer time and tolerated yet higher temperatures. Both properties (growth temperature and temperature tolerance) are used to identify N. asteroides complex (N. farcinica) and N. otitidiscaviarum, and according to our results they are not suitable to differentiate regional strains of this species. The N. asteroides strains assayed showed an ability to grow at and tolerate elevated temperatures superior to those belonging to the other species. Although adaptation of local N. asteroides and N. otitidiscaviarum strains to temperature is important, it is more significant for N. brasiliensis, because this species is predominant in the Tucumán soil and responsible for the major number of diseases in the area.

Argentina↗
PubMed2001

[French neurosurgery in the Bosnia-Herzegovina conflict].

Seven French neurosurgical missions, from June 1994 to December 1996, were sent successively to Bosnia-Herzegovina with the help of a non-governmental organisation Médecins du Monde. The aim of this article is to present the working conditions, make an overall evaluation of the missions and then to draw lessons and discuss the limits. The initial aim of these neurosurgical missions was: i) to provide human and logistic support to the Bosniac teams in the field; ii) to exchange knowledge and help in the training of local young neurosurgeons; iii) to be present as witnesses. The towns of Tuzla and Zenica in Eastern and Central Bosnia respectively were chosen as the missions bases. One hundred five neurosurgical operations were carried out in precarious conditions, particularly concerning anesthesia. The largest number of the operations (52%) concerned standard neurosurgical pathologies, without any direct link to the war but which had been put off or made difficult due to the war. Cranioplasties and peripheric nerve injuries were the main lesions directly related to the war situation which the French missions had to deal with. Actually, war neurosurgical pathologies were very often dealt with in emergency by Bosniac teams in the field hospitals near the front. Previously existing neurosurgical environment, in particular with access to a scanner is an absolute necessity to carry out a good quality neurosurgical mission. Precarious anesthesia and operating conditions require the surgical team to adapt to local conditions, but are not a contra-indication to such missions. Although help in the field can prove useful on occasions, training the resident teams is important. This can be done locally, but additional training in a neurosurgically developed country is fundamental. Missions such as these require relatively major funding (about 150 000 French francs for each of our missions) and suitable infrastructures. Prior to undertaking this type of mission, a neurosurgeon must evaluate local human and equipment needs.

Bosnia and Herzegovina↗
PubMed1994

The types of drugs used by HIV-infected injection drug users in a multistate surveillance project: implications for intervention.

OBJECTIVES: This study sought to describe the drugs used by drug injectors infected with human immunodeficiency virus (HIV) and to determine factors associated with the primary injection drug used. METHODS: A cross-section of persons 18 years of age or older reported with HIV or acquired immunodeficiency syndrome (AIDS) to local health departments in 11 US states and cities was surveyed. RESULTS: Of 4162 persons interviewed, 1147 (28%) reported ever having injected drugs. Of these 1147 injectors, 72% primarily injected a drug other than heroin. However, the types of drugs injected varied notably by place of residence. Heroin was the most commonly injected drug in Detroit (94%) and Connecticut (48%); cocaine was the most common in South Carolina (64%), Atlanta (56%), Delaware (55%), Denver (46%), and Arizona (44%); speedball was most common in Florida (46%); and amphetamines were most common in Washington (56%). Other determinants of the type of drug primarily injected were often similar by region of residence, except for heroin use. Polysubstance abuse was common; 75% injected more than one type of drug, and 85% reported noninjected drug use. CONCLUSIONS: Preventing the further spread of HIV will require more drug abuse treatment programs that go beyond methadone, address polysubstance abuse, and adapt to local correlates of the primary drug used.

Adolescent↗
PubMed2005

Regionally isolated populations of an imperiled Caribbean coral, Acropora palmata.

The movements of larvae between marine populations are difficult to follow directly and have been the subject of much controversy, especially in the Caribbean. The debate centres on the degree to which populations are demographically open, such that depleted populations can be replenished by recruitment from distant healthy populations, or demographically closed and thus in need of local management. Given the depressed state of many tropical reef populations, the understanding of these movements now bears critically on the number, placement, and size of marine reserves. Most genetic analyses assume that dispersal patterns have been stable for thousands of generations, thus they commonly reflect past colonization histories more than ongoing dispersal. Recently developed multilocus genotyping approaches, however, have the demonstrated ability to detect both migration and population isolation over far shorter timescales. Previously, we developed five microsatellite markers and demonstrated them to be both Mendelian and coral-specific. Using these markers and Bayesian analyses, we show here that populations of the imperiled reef-building coral, Acropora palmata, have experienced little or no recent genetic exchange between the western and the eastern Caribbean. Puerto Rico is identified as an area of mixing between the two subregions. As a consequence of this regional isolation, populations in the western and eastern Caribbean should have the potential to adapt to local conditions and will require population-specific management strategies.

Animals↗
PubMed2003

A toolkit for trainer appraisal and development.

All GPs are required to undergo formal revalidation and appraisal. Revalidation and re-accreditation assess past performance with a view to licensing future activity. GP trainers have additional responsibilities for delivering high quality education to tomorrow's doctors beyond those of a GP. In order to fulfill this role trainers are required to attend re-accreditation courses by their local educational establishments and will have different needs to those of their doctor role. Course organizers have responsibilities that include the organisation and assurance of quality of the training provided by their scheme. Although there are no absolute definitions of good quality teaching, it is widely accepted that proxy measures for both consulting and teaching are important and definable. In the case of teaching registrars, these include provision for welcoming, inducting and informing new registrars, assessing their needs, and providing a climate in which they can flourish, as well as actually teaching them. This toolkit explores a system of appraisal designed to help trainers achieve these tasks efficiently, using structured feedback from registrars as well as the trainers' own reports as a basis for discussion during an appraisal interview. It contains some hints for interviewers and comments on the likely issues to emerge, as well as the basic tools needed to conduct the process. The toolkit can be adapted for local use. It has been well received by the trainers, and refined in the light of their feedback.

Clinical Competence↗
PubMed2025

Repeated evolution of photoperiodic plasticity by different genetic architectures during recurrent colonizations in a butterfly.

In cases of recurrent colonizations of similar habitats from the same base population, it is commonly expected that repeated phenotypic adaptation is caused by parallel changes in genetic variation. However, it is becoming increasingly clear that similar phenotypic variation may also evolve by alternative genetic pathways. Here, we explore the repeated evolution of photoperiodic plasticity for diapause induction across Swedish populations of the speckled wood butterfly, Pararge aegeria. This species has colonized Scandinavia at least twice, and population genomic results show that one of the candidate regions associated with spatial variation in photoperiodism is situated on the Z-chromosome. Here, we assay hybrid crosses between several populations that differ in photoperiodic plasticity for sex-linked inheritance of the photoperiodic reaction norm. We find that while a cross between more distantly related populations from the two different colonization events shows strong sex-dependent inheritance of photoperiodic plasticity, a cross between two more closely related populations within the oldest colonization range shows no such effect. We conclude that the genotype-phenotype map for photoperiodic plasticity varies across these populations and that similar local phenotypic adaptation has evolved during recurrent colonization events by partly non-parallel genetic changes.

Butterflies↗
PubMed1999

Dissociation of peak vascular conductance and V(O2) max among highly trained athletes.

Previously, a strong relationship has been found between whole body maximal aerobic power (VO(2 max)) and peak vascular conductance in the calf muscle (J. L. Reading, J. M. Goodman, M. J. Plyley, J. S. Floras, P. P. Liu, P. R. McLaughlin, and R. J. Shephard. J. Appl. Physiol. 74: 567-573, 1993; P. G. Snell, W. H. Martin, J. C. Buckley, and C. G. Blomqvist. J. Appl. Physiol. 62: 606-610, 1987), suggesting a matching between maximal exercise capacity and peripheral vasodilatory reserve across a broad range of aerobic power. In contrast, long-term training could alter this relationship because of the unique demands for muscle blood flow and cardiac output imposed by different types of training. In particular, the high local blood flows but relatively low cardiac output demand imposed by the type of resistance training used by bodybuilders may cause a relatively greater development in peripheral vascular reserve than in aerobic power. To examine this possibility, we studied the relationship between treadmill VO(2 max) and vascular conductance in the calf by using strain-gauge plethysmography after maximal ischemic plantar flexion exercise in 8 healthy sedentary subjects (HS) and 28 athletes. The athletes were further divided into three groups: 10 elite middle-distance runners (ER), 11 power athletes (PA), and 7 bodybuilders (BB). We found that both BB and ER deviate from the previously demonstrated relationship between VO(2 max) and vascular conductance. Specifically, for a given vascular conductance, BB had a lower VO(2 max), whereas ER had a higher VO(2 max) than did HS and PA. We conclude that the relationship between peak vascular conductance and aerobic power is altered in BB and ER because of training-specific effects on central vs. peripheral cardiovascular adaptation to local skeletal muscle metabolic demand.

Blood Vessels↗
PubMed2005

Marine radiations at small geographic scales: speciation in neotropical reef gobies (Elacatinus).

Studies of speciation in the marine environment have historically compared broad-scale distributions and estimated larval dispersal potential to infer the geographic barriers responsible for allopatric speciation. However, many marine clades show high species diversity in geographically restricted areas where barriers are not obvious and estimated dispersal potential should bring many sister taxa into contact. Genetic differentiation at small (separation < 1000 km) spatial scales could facilitate speciation by mechanisms other than the gradual accumulation of reproductive isolation during extended allopatry, such as ecological adaptation to local environmental conditions or the rapid evolution of genes tied to mate recognition, but the role of each of these possibilities has not been simultaneously explored for any species-rich marine taxon. Here, we develop a robust phylogenetic framework for 31 taxa from a species-rich group of Neotropical reef fishes (Gobiidae: Elacatinus) using 3230 bp from one mitochondrial and two nuclear gene regions. We use this framework to explore the contribution of large- and small-scale geographic isolation, ecological differentiation, and coloration toward the formation and maintenance of species. Although species of Elacatinus occur on both sides of the Isthmus of Panama, no sister species are separated by this barrier. Instead, our results indicate that sister taxa occur within oceans. Sister taxa usually differ by coloration, and more distantly related sympatric species frequently differ by resource use. This suggests that some combination of coloration and ecological differences may facilitate assortative mating at range boundaries or in sympatry. Overall, speciation in Elacatinus is consistent with a model of recurring adaptive radiations in stages taking place at small geographic scales.

Animals↗
PubMed2005

Sphingosine-1-phosphate acts via rho-associated kinase and nitric oxide to regulate human placental vascular tone.

Sphingosine-1-phosphate (S1P), a bioactive lipid released from activated platelets, has been demonstrated in animal models to regulate vascular tone through receptor-mediated activation of Rho-associated kinase 1 and nitric oxide synthase 3. The role of S1P in regulation of human vascular tone (particularly during pregnancy, with its unique vascular adaptations and localized platelet activation) is unknown. We hypothesized that S1P would constrict small placental arteries through activation of Rho-associated kinases with modulation by nitric oxide. Reverse transcription-polymerase chain reaction of chorionic plate artery preparations detected mRNAs encoding all five receptors for S1P, and S1P induced dose-dependent vasoconstriction of both chorionic plate and stem villous isobarically mounted arteries, which at 10 micromol/L was 32.9% +/- 3.86% (mean +/- SEM) and 34.6% +/- 7.01%, respectively. In stem villous arteries, S1P-induced vasoconstriction was enhanced significantly following inhibition of nitric oxide synthases with N(G)-nitro-L-arginine methyl ester (100 micromol/L, 52.6% +/- 6.28%, P < 0.05). The S1P-induced vasoconstriction was reversed by Y27632, an inhibitor of Rho-associated kinases (10 micromol/L) in both chorionic plate (to 14.9% +/- 4.95%) and stem villous arteries (to 2.71% +/- 6.13%). The S1P added to alpha-toxin-permeabilized, isometrically mounted chorionic plate arteries bathed in submaximal Ca(2+)-activating solution induced Ca(2+)-sensitization of constriction, which was 47.7% +/- 10.0% of that occurring to maximal Ca(2+)-activating solution. This was reduced by Y27632 to 18.4% +/- 18.4%. Interestingly, S1P-induced vasoconstriction occurred in all isobarically mounted arteries but was inconsistent in isometrically mounted chorionic plate arteries. In summary, S1P-induced vasoconstriction in human placental arteries is mediated by increased Ca(2+)-sensitization through activation of Rho-associated kinases, and this vasoconstriction also is modulated by nitric oxide. Identification of these actions of S1P in the placental vasculature is important for understanding both normal and potentially abnormal vascular adaptations with pregnancy.

Arteries↗
PubMed2025

Intraspecific divergence within Microcystis aeruginosa mediates the dynamics of freshwater harmful algal blooms under climate warming scenarios.

Intraspecific biodiversity can have ecosystem-level consequences and may affect the accuracy of ecological forecasting. For example, rare genetic variants may have traits that prove beneficial under future environmental conditions. The cyanobacterium responsible for most freshwater harmful algal blooms worldwide, Microcystis aeruginosa, occurs in at least three types. While the dominant type occurs in eutrophic environments and is adapted to thrive in nutrient-rich conditions, two additional types have recently been discovered that inhabit oligotrophic and eutrophic environments and have genomic adaptations for survival under nutrient limitation. Here, we show that these oligotrophic types are widespread throughout the Eastern USA. By pairing an experimental warming study with gene expression analyses, we found that the eutrophic type may be most susceptible to climate warming. In comparison, oligotrophic types maintained their growth better and persisted longer under warming. As a mechanistic explanation for these patterns, we found that oligotrophic types responded to warming by widespread elevated expression of heat shock protein genes. Reduction of nutrient loading has been a historically effective mitigation strategy for controlling harmful algal blooms. Our results suggest that climate warming may benefit oligotrophic types of M. aeruginosa, potentially reducing the effectiveness of such mitigation efforts. In-depth study of intraspecific variation may therefore improve forecasting for understanding future whole ecosystem dynamics.

Microcystis↗
PubMed2003

Genetics of drought adaptation in Arabidopsis thaliana: I. Pleiotropy contributes to genetic correlations among ecological traits.

We examined patterns of genetic variance and covariance in two traits (i) carbon stable isotope ratio delta13C (dehydration avoidance) and (ii) time to flowering (drought escape), both of which are putative adaptations to local water availability. Greenhouse screening of 39 genotypes of Arabidopsis thaliana native to habitats spanning a wide range of climatic conditions, revealed a highly significant positive genetic correlation between delta13C and flowering time. Studies in a range of C3 annuals have also reported large positive correlations, suggesting the presence of a genetically based trade-off between mechanisms of dehydration avoidance (delta13C) and drought escape (early flowering). We examined the contribution of pleiotropy by using a combination of mutant and near-isogenic lines to test for positive mutational covariance between delta13C and flowering time. Ecophysiological mutants generally showed variation in delta13C but not flowering time. However, flowering time mutants generally demonstrated pleiotropic effects consistent with natural variation. Mutations that caused later flowering also typically resulted in less negative delta13C and thus probably higher water use efficiency. We found strong evidence for pleiotropy using near-isogenic lines of Frigida and Flowering locus C, cloned loci known to be responsible for natural variation in flowering time. These data suggest the correlated evolution of delta13C and flowering time is explained in part by the fixation of pleiotropic alleles that alter both delta13C and time to flowering.

Adaptation, Biological↗
PubMed2005

AmyA, an alpha-amylase with beta-cyclodextrin-forming activity, and AmyB from the thermoalkaliphilic organism Anaerobranca gottschalkii: two alpha-amylases adapted to their different cellular localizations.

Two alpha-amylase genes from the thermophilic alkaliphile Anaerobranca gottschalkii were cloned, and the corresponding enzymes, AmyA and AmyB, were investigated after purification of the recombinant proteins. Based on their amino acid sequences, AmyA is proposed to be a lipoprotein with extracellular localization and thus is exposed to the alkaline milieu, while AmyB apparently represents a cytoplasmic enzyme. The amino acid sequences of both enzymes bear high similarity to those of GHF13 proteins. The different cellular localizations of AmyA and AmyB are reflected in their physicochemical properties. The alkaline pH optimum (pH 8), as well as the broad pH range, of AmyA activity (more than 50% activity between pH 6 and pH 9.5) mirrors the conditions that are encountered by an extracellular enzyme exposed to the medium of A. gottschalkii, which grows between pH 6 and pH 10.5. AmyB, on the other hand, has a narrow pH range with a slightly acidic pH optimum at 6 to 6.5, which is presumably close to the pH in the cytoplasm. Also, the intracellular AmyB is less tolerant of high temperatures than the extracellular AmyA. While AmyA has a half-life of 48 h at 70 degrees C, AmyB has a half-life of only about 10 min at that temperature, perhaps due to the lack of stabilizing constituents of the cytoplasm. AmyA and AmyB were very similar with respect to their substrate specificity profiles, clearly preferring amylose over amylopectin, pullulan, and glycogen. Both enzymes also hydrolyzed alpha-, beta-, and gamma-cyclodextrin. Very interestingly, AmyA, but not AmyB, displayed high transglycosylation activity on maltooligosaccharides and also had significant beta-cyclodextrin glycosyltransferase (CGTase) activity. CGTase activity has not been reported for typical alpha-amylases before. The mechanism of cyclodextrin formation by AmyA is unknown.

Adaptation, Physiological↗
PubMed2003

Estimating photosynthetic radiation use efficiency using incident light and photosynthesis of individual leaves.

It has been theorized that photosynthetic radiation use efficiency (PhRUE) over the course of a day is constant for leaves throughout a canopy if leaf nitrogen content and photosynthetic properties are adapted to local light so that canopy photosynthesis over a day is optimized. To test this hypothesis, 'daily' photosynthesis of individual leaves of Solanum melongena plants was calculated from instantaneous rates of photosynthesis integrated over the daylight hours. Instantaneous photosynthesis was estimated from the photosynthetic responses to photosynthetically active radiation (PAR) and from the incident PAR measured on individual leaves during clear and overcast days. Plants were grown with either abundant or scarce N fertilization. Both net and gross daily photosynthesis of leaves were linearly related to daily incident PAR exposure of individual leaves, which implies constant PhRUE over a day throughout the canopy. The slope of these relationships (i.e. PhRUE) increased with N fertilization. When the relationship was calculated for hourly instead of daily periods, the regressions were curvilinear, implying that PhRUE changed with time of the day and incident radiation. Thus, linearity (i.e. constant PhRUE) was achieved only when data were integrated over the entire day. Using average PAR in place of instantaneous incident PAR increased the slope of the relationship between daily photosynthesis and incident PAR of individual leaves, and the regression became curvilinear. The slope of the relationship between daily gross photosynthesis and incident PAR of individual leaves increased for an overcast compared with a clear day, but the slope remained constant for net photosynthesis. This suggests that net PhRUE of all leaves (and thus of the whole canopy) may be constant when integrated over a day, not only when the incident PAR changes with depth in the canopy, but also when it varies on the same leaf owing to changes in daily incident PAR above the canopy. The slope of the relationship between daily net photosynthesis and incident PAR was also estimated from the photosynthetic light response curve of a leaf at the top of the canopy and from the incident PAR above the canopy, in place of that measured on individual leaves. The slope (i.e. net PhRUE) calculated in this simple way did not differ statistically from that calculated using data from individual leaves.

Adaptation, Physiological↗