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PubMed2000

An open architecture for medical imaging systems.

Integration of medical imaging is the goal of many standards. Interfile and Digital Imaging and Communications in Medicine (DICOM) standards have made great strides in this area. The impact of DICOM is greater owing to its wider acceptance. However, the lack of conformance testing makes interoperability difficult, often requiring expensive consulting teams in a mixed-vendor environment. DICOM is difficult to learn and deploy because it does not use modern software paradigms. Many hardware and software advances in computer architectures and communications could greatly enhance diagnostic imaging if they could be quickly incorporated into medical imaging standards. These problems led to consideration of a solution able to take advantage of state-of-the-art technology and to allow diverse implementations while ensuring the accurate interchange of information between health care providers. It is an object-oriented system information model, with the common object request broker architecture (CORBA) as the vehicle to ensure interoperability between different implementations of the model. This report presents the model.

Computer Communication Networks↗
PubMed1993

The operational impact of architectural alternatives for radiological imaging workstations.

Characteristics of workstations for use in digital radiological imaging have been investigated for many years. However, much of this investigation has focused on the workstation in isolation, and has often been directed almost entirely at user interface issues. Certainly these issues are critical, but with the increasing use of commercial workstations it is important to look at the workstation in the context of the medical information environment and examine some important underlying characteristics required to meet the demands of digital radiology. This article examines the role of storage components in these workstations both architecturally and operationally. Both aspects are viewed with consideration of their impact on the internals of the workstation and its interaction with the external information system. By considering these aspects of the workstation it is apparent that local storage and image preloading are required to support diagnostic viewing. Additional operational and architectural strategies are required to efficiently manage information within the workstation.

Computer Communication Networks↗
PubMed1999

Virtual management of radiology examinations in the virtual radiology environment using common object request broker architecture services.

In the Department of Defense (DoD), US Army Medical Command is now embarking on an extremely exciting new project--creating a virtual radiology environment (VRE) for the management of radiology examinations. The business of radiology in the military is therefore being reengineered on several fronts by the VRE Project. In the VRE Project, a set of intelligent agent algorithms determine where examinations are to routed for reading bases on a knowledge base of the entire VRE. The set of algorithms, called the Meta-Manager, is hierarchical and uses object-based communications between medical treatment facilities (MTFs) and medical centers that have digital imaging network picture archiving and communications systems (DIN-PACS) networks. The communications is based on use of common object request broker architecture (CORBA) objects and services to send patient demographics and examination images from DIN-PACS networks in the MTFs to the DIN-PACS networks at the medical centers for diagnosis. The Meta-Manager is also responsible for updating the diagnosis at the originating MTF. CORBA services are used to perform secure message communications between DIN-PACS nodes in the VRE network. The Meta-Manager has a fail-safe architecture that allows the master Meta-Manager function to float to regional Meta-Manager sites in case of server failure. A prototype of the CORBA-based Meta-Manager is being developed by the University of Arizona's Computer Engineering Research Laboratory using the unified modeling language (UML) as a design tool. The prototype will implement the main functions described in the Meta-Manager design specification. The results of this project are expected to reengineer the process of radiology in the military and have extensions to commercial radiology environments.

Algorithms↗
PubMed2007

Epigenetic control of nuclear architecture.

The cell nucleus is a highly structured compartment where nuclear components are thought to localize in non-random positions. Correct positioning of large chromatin domains may have a direct impact on the localization of other nuclear components, and can therefore influence the global functionality of the nuclear compartment. DNA methylation of cytosine residues in CpG dinucleotides is a prominent epigenetic modification of the chromatin fiber. DNA methylation, in conjunction with the biochemical modification pattern of histone tails, is known to lock chromatin in a close and transcriptionally inactive conformation. The relationship between DNA methylation and large-scale organization of nuclear architecture, however, is poorly understood. Here we briefly summarize present concepts of nuclear architecture and current data supporting a link between DNA methylation and the maintenance of large-scale nuclear organization.

Animals↗
PubMed1997

Non-native architectures in protein design and mimicry.

Protein design aims to mimic some of the structural and functional properties of native proteins. The complexity of the folding mechanism, i.e. the pathway by which a linear polypeptide chain finds its unique 3D-structure, represents one of the most intriguing hurdles in this rapidly growing field. In order to bypass this well-known protein-folding problem, some years ago we proposed the construction of non-native chain architectures with a high propensity for folding. According to this concept, termed TASP (template-assembled synthetic proteins), topological templates are used as a built-in device for directing covalently attached peptide blocks to a predetermined packing arrangement, resulting in branched chain architectures. Recent progress in the synthetic methodology for assembling peptides now allows us to access the full potential of the TASP concept. In this article, we discuss the state of the art of template-based protein de novo design, with special emphasis on progress in peptide synthesis and template design and show that some fundamental questions in protein assembly, structure and function can be approached by designing protein mimetics of reduced structural and functional complexity.

Drug Design↗
PubMed2005

Decrease of knee flexion torque in patients with ACL reconstruction: combined analysis of the architecture and function of the knee flexor muscles.

A decrease of deep knee flexion torque after anterior cruciate ligament (ACL) reconstruction, using a semitendinosus (and gracilis) tendon, has been reported. However, the cause of this weakness remains controversial. Architectural and functional differences in the knee flexor muscles influence this weakness. the fiber length of the semitendinosus, gracilis, semimembranosus, and biceps femoris were directly measured in six human cadavers. The flexion torque and EMG of the hamstrings were measured in both limbs of 16 patients (23+/-5 years) after ACL reconstruction (12-43 months post-operation), using ipsilateral semitendinosus tendon. Magnetic resonance imagings were taken, over both the thighs of those patients, to measure muscle volume and to confirm a state of semitendinosus tendon regeneration. The position of the musculotendinous junction of the semitendinosus was also analyzed. The fiber length of the semitendinosus and gracilis were three to four times longer than that of the semimembranosus and biceps femoris. The difference of flexion torque between the normal and ACL reconstructed limbs significantly increased as the knee flexion angle increased. The EMG value for the semimembranosus and biceps femoris of both limbs as well as the semitendinosus of the ACL reconstructed limbs, significantly reduced as the knee flexion angle was increased. The volume of the semitendinosus in the reconstructed limb was significantly smaller than in normal limbs. The regeneration of the semitendinosus tendon was confirmed in all subjects, and the musculotendinous junction position of the reconstructed limb in almost all subjects was found in further image from the knee joint space than that for the normal limb. The decrease of deep knee flexion torque, after ACL reconstruction, could be due to the atrophy and shortening of the semitendinosus after its tendon has been harvested, as well as the lack of compensation from the semimembranosus and biceps femoris, due to the architectural differences between the semitendinosus and the semimembranosus and biceps femoris.

Achilles Tendon↗
PubMed2004

Long-term prediction of three-dimensional bone architecture in simulations of pre-, peri- and post-menopausal microstructural bone remodeling.

The mechanical behavior of trabecular bone depends on the internal bone structure. It is generally accepted now that the trabecular bone structure is a result of a load adaptive bone remodeling. The mathematical laws that relate bone remodeling to the local state of stress and strain, however, are still under investigation. The aim of this project was to investigate if changes in the trabecular architecture as observed with age-related bone loss and osteoporosis can be predicted from a computer model that simulates bone resorption after hormone depletion based on realistic models of trabecular microstructure using micro-computed tomography (muCT). A compact desktop muCT providing a nominal isotropic resolution of 14 mum was used to measure two groups of seven trabecular bone specimens from pre-menopausal and post-menopausal women respectively. A novel algorithm was developed to simulate age-related bone loss for the specimens in the first group. The algorithm, also referred to as simulated bone atrophy (SIBA), describes a truly three-dimensional approach and is based directly on cellular bone remodeling with an underlying realistic time frame. Bone resorption is controlled by osteoclastic penetration depth and bone formation is governed by the efficiency level of the osteoblasts. The simulation itself describes an iterative process with a cellular remodeling cycle of 197 days. Activation frequency is controllable and can be adjusted for the different phases of pre-, peri- and post-menopause. For our simulations, osteoblastic and osteoclastic activities were in balance until the onset of menopause, set to be at the age of 50 years. In that period, the structure remained almost constant. After the onset of menopause an imbalance in the cell activities was modeled resulting in a net bone loss. The doubling of the activation frequency in the peri-menopausal phase caused a pronounced loss. Using advanced animation tools and quantitative bone morphometry, the changes in bone architecture associated with the bone loss were monitored over an average observation time of 43 years until the age of 80 years. In that time, bone volume density decreased monotonously with the progression of the simulation for all specimens. Right after the onset of menopause, bone was lost fast, where with the progression of age losses slowed down. The structures at the end-point of the simulations were then compared qualitatively and quantitatively to the structures of the post-menopausal group with all morphometric indices being within a narrow margin of error. These results suggest the feasibility of transforming "normal" to "osteopenic" bone on a microstructural level yielding in realistic bone models similar in appearance as well as in structural behavior if compared to a post-menopausal group of women.

Aged↗
PubMed1999

Trabecular bone architecture in the distal radius using magnetic resonance imaging in subjects with fractures of the proximal femur. Magnetic Resonance Science Center and Osteoporosis and Arthritis Research Group.

To determine whether magnetic resonance (MR)-derived measures of trabecular bone architecture in the distal radius are predictive for prevalent hip fractures, 20 subjects with hip fractures and 19 age-matched postmenopausal controls were studied. Bone mineral density (BMD) measures at the hip (dual-energy X-ray absorptiometry, DXA) and the distal radius (peripheral quantitative computed tomography, pQCT) were also obtained. We compared the MR-based structural measures derived in the radius with those in the calcaneus of the same patients. In the radius, images were acquired at an in-plane resolution of 156 microm and a slice thickness of 0.5 mm. Stereologic measures such as the apparent trabecular thickness (app. Tb.Th), fractional trabecular bone volume (app. BV/TV), trabecular spacing (app. Tb.Sp) and trabecular number (app. Tb.N) were derived from the images. Measures of app. Tb.Sp and app. Tb.N in the distal radius showed significant (p<0.05) differences between the two groups, as did hip BMD measures. However, radial trabecular BMD measures showed only a marginal difference (p = 0.05). Receiver operating curve analysis was used to determine the diagnostic efficacy of BMD, structural measures and a combination of the two. The area under the curve (AUC) for total hip BMD was 0.73, and for radial trabecular BMD was 0.69. AUC for most of the measures of trabecular bone structure at the distal radius was lower than for hip BMD measures; however, AUC for app. Tb.N at the radius was 0.69, comparable to trabecular BMD using pQCT. The AUC for combined BMD (hip) and structure measures was higher (0.87) when radius and calcaneus structure was included. Measures of trabecular architecture derived from MR images combined with BMD measures improve the discrimination between subjects with hip fractures and normal age-matched controls.

Aged↗
PubMed1998

Feline caudofemoralis muscle. Muscle fibre properties, architecture, and motor innervation.

Feline caudofemoralis (CF) is a promising preparation in which to study the properties of mammalian fast-twitch skeletal muscle, but little is known about its muscle fiber properties, architecture, and motor innervation. We used histochemical techniques to confirm that it contained predominantly type IIB fibers (95+/-2%, n=8, with six of eight muscles composed exclusively of type IIA and IIB fibers), but physiological experiments showed less fatiguability than for the type IIB component of medial gastrocnemius. This may be related to the surprisingly strong and regular recruitment of CF during repetitive tasks such as walking and trotting, which we demonstrated electromyographically. We measured muscle length over the anatomical range of motion for CF (approximately 0.6-1.2 L0) and estimated working length during walking and trotting (approximately 0.95-1.15 L0). The specific tension was similar to that of the exclusively slow-twitch soleus muscle (31.2+/-4.7 N/cm2 compared with 31.8+/-4.1 N/cm2; P>0.8). Single fiber dissections of CF revealed a series-fibered architecture with a mean of 2.3 fibers, each 2.5 cm long, required to span the fascicle length. We identified two neuromuscular compartments in CF by cutting one of the two nerve branches innervating CF and depleting the glycogen stores in the intact motor units. These compartments were in parallel and extended the length of the muscle; their electromyographic activity was similar during various natural behaviors. CF and gluteus maximus motoneurons were labeled concurrently with a combination of fluorescent, retrograde tracers including Fluororuby, Fluorogold and Fast Blue. The CF motor nucleus was located in L7-S1, overlapping and intermingling extensively with the nucleus of the adjacent gluteus maximus muscle. Distributions of CF motoneuron diameter revealed one large peak around 50-55 microm, with relatively few small-diameter (less than 35 microm) cells. Using estimates of the total number of fibers in three muscles and the estimated number of alpha-motoneurons for those same muscles, we calculated a mean innervation ratio of approximately 270, which is at the low end of the innervation ratios for type IIB motor units from other feline muscles and more similar to type IIA motor units. In general, CF appears to be a useful preparation in which to study the properties of fast-twitch muscle, but these properties may vary somewhat from type IIB fibers from different muscles.

Acetylcholinesterase↗
PubMed2006

Direct electrochemical immunoassay based on a silica nanoparticles/sol-gel composite architecture for encapsulation of immunoconjugate.

A highly hydrophobic and non-toxic colloidal silica nanoparticle/polyvinyl butyral sol-gel composite membrane was prepared on a platinum wire electrode. With diphtheria-toxoid (D-Ag) as a model antigen and encapsulation of diphtheria antibody (D-Ab) in the composite architecture, this membrane could be used for reagentless electrochemical immunoassay. It displayed a porous and homogeneous composite architecture without the aggregation of the immobilized protein molecules. The formation of immunoconjugate by a simple one-step immunoreaction between D-Ag in sample solution and the immobilized D-Ab introduced the change in the potential. Under optimal conditions, the D-Ag analyte could be determined in the linear ranges from 10 to 800 ng ml(-1) with a relatively low detection limit of 2.3 ng ml(-1) at 3delta. The D-Ag immunosensor exhibited good precision, high sensitivity, acceptable stability, accuracy, and reproducibility. This composite membrane could be used efficiently for the entrapment of different biomarkers and clinical applications.

Antigens, Bacterial↗
PubMed1997

Renal cell carcinoma of clear type: correlation of CT features with tumor size, architectural patterns, and pathologic staging.

The purpose of this study was to report the CT findings of renal cell carcinoma of clear type (RCCCT) and to determine if there are characteristic morphologic features in RCCCT with respect to tumor size, architectural patterns, and pathologic stage. The CT scans of 35 patients with RCCCT were reviewed retrospectively. The CT findings (tumor size, attenuation patterns, presence of calcifications, encapsulation, margins of neoplasms, venous involvement by neoplasms) were correlated with tumor size, architectural patterns, and pathologic staging. Of the 35 neoplasms, 28 (80 %) were solid, 4 (11 %) were papillary, and 3 (9 %) were cystic. Complete encapsulation was more frequent in lower pathologic stages (40 % in stages 1 and 2 vs 0 % in stages 3 and 4; p < 0.05). Venous involvement was less frequent with completely encapsulated neoplasms (0 of 10, 0 %) than with incompletely or nonencapsulated neoplasms (8 of 25, 32 %; p < 0.05). Encapsulated RCCCT are more likely to have lower pathologic stage. Nonencapsulated neoplasms are more likely to have a higher pathologic stage.

Adenocarcinoma, Clear Cell↗
PubMed2002

The role of FFM accumulation and skeletal muscle architecture in powerlifting performance.

The purpose of this study was to determine the distribution and architectural characteristics of skeletal muscle in elite powerlifters, and to investigate their relationship to fat-free mat (FFM) accumulation and powerlifting performance. Twenty elite male powerlifters (including four world and three US national champions) volunteered for this study. FFM, skeletal muscle distribution (muscle thickness at 13 anatomical sites), and isolated muscle thickness and fascicle pennation angle (PAN) of the triceps long-head (TL), vastus lateralis, and gastrocnemius medialis (MG) muscles were measured with B-mode ultrasound. Fascicle length (FAL) was calculated. Best lifting performance in the bench press (BP), squat lift (SQT), and dead lift (DL) was recorded from competition performance. Significant correlations (P < or = 0.01) were observed between muscle distribution (individual muscle thickness from 13 sites) and performance of the SQT (r = 0.79 to r = 0.91), BP (r = 0.63 to r = 0.85) and DL (r = 0.70 to r = 0.90). Subscapular muscle thickness was the single best predictor of powerlifting performance in each lift. Performance of the SQT, BP, and DL was strongly correlated with FFM and FFM relative to standing height (r = 0.86 to 0.95, P < or = 0.001). FAL of the triceps long head and vastus lateralis were significantly correlated with FFM (r = 0.59, P < or = 0.01; 0.63, P < or = 0.01, respectively) and performance of the SQT (r = 0.45; r = 0.50, respectively; P < or = 0.05), BP (r = 0.52; r = 0.56, respectively; P < or = 0.05), and DL (r = 0.56; r = 0.54, respectively; P < or = 0.01). A significant positive correlation was observed between isolated muscle thickness and PAN for triceps long-head (r = 0.64, P < or = 0.01) and gastrocnemius medialis (r = 0.48, P < or = 0.05) muscles, but not for vastus lateralis (r = 0.35). PAN was negatively correlated with powerlifting performance. Our results indicate that powerlifting performance is a function of FFM and, therefore, may be limited by the ability to accumulate FFM. Additionally, muscle architecture appears to play an important role in powerlifting performance in that greater fascicle lengths are associated with greater FFM accumulation and powerlifting performance.

Body Height↗
PubMed2004

Diffusive sensitivity to muscle architecture: a magnetic resonance diffusion tensor imaging study of the human calf.

The aim of this study was to examine the diffusive properties of adjacent muscles at rest, and to determine the relationship between diffusive and architectural properties, which are task-specific to muscles. The principle, second, and third eigenvalues, trace of the diffusion tensor, and two anisotropic parameters, ellipsoid eccentricity (e) and fractional anisotropy (FA), of various muscles in the human calf were calculated by diffusion tensor imaging (DTI). Linear correlations of the calculated parameters to the muscle physiological cross-sectional area (PCSA), which is proportional to maximum muscle force, were performed to ascertain any linear relation between muscle architecture and diffusivity. Images of the left calf were acquired from six healthy male volunteers. Seven muscles were investigated in this study. These comprised the soleus, lateral gastrocnemius, medial gastrocnemius, posterior tibialis, anterior tibialis, extensor digitorum longus, and peroneus longus. All data were presented as the mean and standard error of the mean (SEM). In general, differences in diffusive parameter values occurred primarily between functionally different muscles. A strong correlation was also found between PCSA and the third eigenvalue, e, and FA. A mathematical derivation revealed a linear relationship between PCSA and the third eigenvalue as a result of their dependence on the average radius of all fibers within a single muscle. These findings demonstrated the ability of DTI to differentiate between functionally different muscles in the same region of the body on the basis of their diffusive properties.

Diffusion Magnetic Resonance Imaging↗
PubMed1999

An architectural hypothesis for direction selectivity in the visual cortex: the role of spatially asymmetric intracortical inhibition.

Within a linear field approach, an architectural model for simple cell direction selectivity in the visual cortex is proposed. The origin of direction selectivity is related to recurrent intracortical interactions with a spatially asymmetric character along the axis of stimulus motion. No explicit asymmetric temporal mechanisms are introduced or adopted. The analytical investigation of network behavior, carried out under the assumption of a linear superposition of geniculate and intracortical contributions, shows that motion sensitivity of the resulting receptive fields emerges as a dynamic property of the cortical network without any feed-forward direction selectivity bias. A detailed analysis of the effects of the architectural characteristics of the cortical network on directionality and velocity-response curves was conducted by systematically varying the model's parameters.

Animals↗
PubMed2005

Modification of plant architecture through the expression of GA 2-oxidase under the control of an estrogen inducible promoter in Arabidopsis thaliana L.

The gibberellin (GA) 2-oxidase (PcGA2ox1) from bean catalyses the 2beta-hydroxylation of some precursor and bioactive GAs resulting in their inactivation. We have expressed PcGA2ox1 under the control of the estrogen receptor-based chemical-inducible system, XVE, to modify plant architecture and assess whether transgene expression is localised. Applications of estradiol to the shoot apical region of inducible PcGA2ox1 overexpressors exhibited delays in both bolting (maximum of 46 days) and times to anthesis (maximum of 62 days) compared to wildtype (36 and 41 days, respectively), without altering leaf area. Individual treated leaves showed signs of epinasty and became dark green; such estradiol-treated regions maintained these 'green-islands' well beyond the onset of leaf senescence. Northern blots revealed that the PcGA2ox1 transcript could be detected within 1 h of treatment. The level of PcGA2ox1 transcript appeared to peak 3-5 h after estradiol application in both high and semi expressors. Quantitative Reverse Transcription (QRT)-PCR data showed that GA down-regulated genes AtGA3ox1, AtGA20ox1 and SCARECROW-LIKE3 (SCL3) were up-regulated and the GA up-regulated genes AtGA2ox1 and AtExp1 were down-regulated in estradiol-treated leaves of inducible PcGA2ox1 overexpressors; neighbouring non-treated leaves showing no significant changes. Further molecular analyses revealed that expression of the transgene was confined to estradiol-treated leaves only. Expression profiles of GA down- and up-regulated genes in inducer-treated overexpressors appeared to be synchronised with changes in leaf phenotype. These observations suggest that PcGA2ox1 under the control of the XVE system can be used effectively to alter plant architecture in Arabidopsis by localised 2beta-hydroxylation of GAs at estradiol-treated sites.

Arabidopsis↗
PubMed2006

High-resolution episcopic microscopy: a rapid technique for high detailed 3D analysis of gene activity in the context of tissue architecture and morphology.

We describe a new methodology for rapid 2D and 3D computer analysis and visualisation of gene expression and gene product pattern in the context of anatomy and tissue architecture. It is based on episcopic imaging of embryos and tissue samples, as they are physically sectioned, thereby producing inherently aligned digital image series and volume data sets, which immediately permit the generation of 3D computer representations. The technique uses resin as embedding medium, eosin for unspecific tissue staining, and colour reactions (beta-galactosidase/Xgal or BCIP/NBT) for specific labelling of gene activity and mRNA pattern. We tested the potential of the method for producing high-resolution volume data sets of adult human and porcine tissue samples and of specifically and unspecifically stained mouse, chick, quail, frog, and zebrafish embryos. The quality of the episcopic images resembles the quality of digital images of true histological sections with respect to resolution and contrast. Specifically labelled structures can be extracted using simple thresholding algorithms. Thus, the method is capable of quickly and precisely detecting molecular signals simultaneously with anatomical details and tissue architecture. It has no tissue restrictions and can be applied for analysis of human tissue samples as well as for analysis of all developmental stages of embryos of a wide variety of biomedically relevant species.

Animals↗
PubMed2006

Distinctive architecture of the chloroplast genome in the chlorophycean green alga Stigeoclonium helveticum.

The chloroplast genome has experienced many architectural changes during the evolution of chlorophyte green algae, with the class Chlorophyceae displaying the lowest degree of ancestral traits. We have previously shown that the completely sequenced chloroplast DNAs (cpDNAs) of Chamydomonas reinhardtii (Chlamydomonadales) and Scenedesmus obliquus (Sphaeropleales) are highly scrambled in gene order relative to one another. Here, we report the complete cpDNA sequence of Stigeoclonium helveticum (Chaetophorales), a member of a third chlorophycean lineage. This genome, which encodes 97 genes and contains 21 introns (including four putatively trans-spliced group II introns inserted at novel sites), is remarkably rich in derived features and extremely rearranged relative to its chlorophycean counterparts. At 223,902 bp, Stigeoclonium cpDNA is the largest chloroplast genome sequenced thus far, and in contrast to those of Chlamydomonas and Scenedesmus, features no large inverted repeat. Interestingly, the pattern of gene distribution between the DNA strands and the bias in base composition along each strand suggest that the Stigeoclonium genome replicates bidirectionally from a single origin. Unlike most known trans-spliced group II introns, those of Stigeoclonium exhibit breaks in domains I and II. By placing our comparative genome analyses in a phylogenetic framework, we inferred an evolutionary scenario of the mutational events that led to changes in genome architecture in the Chlorophyceae.

Base Sequence↗
PubMed2004

A functional analysis of the crown architecture of tropical forest Psychotria species: do species vary in light capture efficiency and consequently in carbon gain and growth?

The crown architectures of 11 Psychotria species native to Barro Colorado Island, Panama were reconstructed from field measurements of leaf and branch geometry with the three-dimensional simulation model Y-plant. The objective was to assess the role of species differences in architecture in light capture and carbon gain in their natural understory environment. When species were grouped according to their putative light environment preference, the shade tolerant species were found to have a small but significantly higher efficiency of light capture for both diffuse and direct light as compared to the light demanding species. Within each grouping, however, there were few significant differences in light capture efficiency among species. The lower efficiencies of light demanding species was due to slightly higher self-shading and slightly lower angular efficiencies. Simulations of whole plant assimilation showed that light demanding species had greater daily assimilation in both direct and diffuse light due to the significantly greater light availability in the sites where light demanding species were found, as compared to those where shade tolerant species occurred. Among light demanding species, the above ground relative growth rate measured over a 1-year period by applying allometric equations for mass versus linear dimensions, was positively correlated with diffuse PFD and with mean daily assimilation estimated from Y-plant. For the shade tolerant plants, there was no significant correlation between RGR and mean daily assimilation or with any measure of light availability, probably because they occurred over a much narrower range of light environments. Overall, the results reveal a strong convergence in light capture efficiencies among the Psychotria species at lower values than previously observed in understory plants using similar approaches. Constraints imposed by other crown functions such as hydraulics and biomechanical support may place upper limits on light capture efficiency.

Biometry↗