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PubMed2004

The roles of ethylene, auxin, abscisic acid, and gibberellin in the hyponastic growth of submerged Rumex palustris petioles.

Rumex palustris responds to complete submergence with upward movement of the younger petioles. This so-called hyponastic response, in combination with stimulated petiole elongation, brings the leaf blade above the water surface and restores contact with the atmosphere. We made a detailed study of this differential growth process, encompassing the complete range of the known signal transduction pathway: from the cellular localization of differential growth, to the hormonal regulation, and the possible involvement of a cell wall loosening protein (expansin) as a downstream target. We show that hyponastic growth is caused by differential cell elongation across the petiole base, with cells on the abaxial (lower) surface elongating faster than cells on the adaxial (upper) surface. Pharmacological studies and endogenous hormone measurements revealed that ethylene, auxin, abscisic acid (ABA), and gibberellin regulate different and sometimes overlapping stages of hyponastic growth. Initiation of hyponastic growth and (maintenance of) the maximum petiole angle are regulated by ethylene, ABA, and auxin, whereas the speed of the response is influenced by ethylene, ABA, and gibberellin. We found that a submergence-induced differential redistribution of endogenous indole-3-acetic acid in the petiole base could play a role in maintenance of the response, but not in the onset of hyponastic growth. Since submergence does not induce a differential expression of expansins across the petiole base, it is unlikely that this cell wall loosening protein is the downstream target for the hormones that regulate the differential cell elongation leading to submergence-induced hyponastic growth in R. palustris.

Abscisic Acid↗

PubMed1993

[A comparison of ankle fixation between two kinds of low-temperature plastic anterior ankle foot orthoses].

The low-temperature ankle foot orthosis (AFO) was designed in the anterior leaf type, called anterior AFO, to meet the need of indoor barefoot walking. It could be easily molded and remolded to fit the foot, as well as to adjust the position of the foot and ankle. Two kinds of low-temperature plastic anterior ankle foot orthoses, anterior encased and anterior direct molding ankle foot orthoses, were compared to analyze the effectiveness of ankle fixation in plantar flexion and inversion. Force was applied to each of the anterior AFOs at the anterior-middle and anterior-lateral sides to simulate the movement of ankle plantar flexion and inversion. At the same time, the deformation in plantar flexion and inversion of both anterior AFOs were recorded to analyze the relationship between force and the deformed angle. The results showed that plantar flexion deformed angles of the anterior direct molding AFO were 2.6 times more flexible than anterior encased AFO. The ankle inversion deformed angles of the anterior direct molding AFO were 3 times more flexible than the anterior encased AFO in inversion. These results support our belief that anterior encased AFO is more effective in controlling ankle plantar flexion and inversion than anterior direct molding AFO, especially for severe spastic hemiplegia in gait correction.

Ankle Joint↗

PubMed2005

Hydrophobicity, adhesion, and friction properties of nanopatterned polymers and scale dependence for micro- and nanoelectromechanical systems.

Applications in micro/nanoelectromechanical systems generally require low adhesion and friction values between two materials of interest. By alteration of the material combinations and surface roughness, including nanopatterning, adhesion and friction can be tailored to meet a specific requirement. Surfaces found in nature, such as hydrophobic lotus leaves, provide a good example of this optimization. Recent models of hydrophobic leaf surfaces show a correlation between roughness and hydrophobicity, which can be mimicked by the presence of nanopatterned asperities on a polymer surface. In addition, by introducing nanopatterns on the polymer surface, the real area of contact decreases when another surface comes into contact with the patterned surface, which reduces adhesion and friction. This study explores the effect of nanopatterning on hydrophobicity, adhesion, and friction for two different hydrophilic polymers, poly(methyl methacrylate) (PMMA) and polyurethane acrylate (MINS), with two types of patterned asperities, low aspect ratio and high aspect ratio, investigated by use of an atomic/friction force microscope (AFM/FFM). In addition to the polymers, a hydrophobic coating was deposited on the surface of the patterned PMMA to study the effect of roughness on the contact angle, along with adhesion and friction. Relative contribution due to change in contact angle and real area of contact are explored. Scale dependence on adhesion and friction was also studied using AFM tips of various radii. Since applications of these surfaces will require operation in varying environments, the effect of relative humidity is investigated.

Acrylates↗

PubMed2001

The MLC tongue-and-groove effect on IMRT dose distributions.

We have investigated the tongue-and-groove effect on the IMRT dose distributions for a Varian MLC. We have compared the dose distributions calculated using the intensity maps with and without the tongue-and-groove effect. Our results showed that, for one intensity-modulated treatment field, the maximum tongue-and-groove effect could be up to 10% of the maximum dose in the dose distributions. For an IMRT treatment with multiple gantry angles (> or = 5), the difference between the dose distributions with and without the tongue-and-groove effect was hardly visible, less than 1.6% for the two typical clinical cases studied. After considering the patient setup errors, the dose distributions were smoothed with reduced and insignificant differences between plans with and without the tongue-and-groove effect. Therefore, for a multiple-field IMRT plan (> or = 5), the tongue-and-groove effect on the IMRT dose distributions will be generally clinically insignificant due to the smearing effect of individual fields. The tongue-and-groove effect on an IMRT plan with small number of fields (< 5) will vary depending on the number of fields in a plan (coplanar or non-coplanar), the MLC leaf sequences and the patient setup uncertainty, and may be significant (> 5% of maximum dose) in some cases, especially when the patient setup uncertainty is small (< or = 2 mm).

Bone Neoplasms↗

PubMed1970

Choice of rotation rate for the horizontal clinostat.

A series of nine rates of rotation of the clinostat were tested to determine optimal and acceptable conditions for simulating weightlessness in plants. Young seedlings of wheat (Triticum aestivum L.) developed roots and coleoptiles of equal lengths and with the same orientation angles over a range of rotation rates from 0.25 to 480 minutes per revolution. Rates from 0.25 to 3 minutes per revolution provided for maximal epinastic curvatures of leaves and branches of Coleus blumei Benth. except for a reduced mean curvature of branches at 0.25 minute per revolution, due probably to physical disturbances in their growth. Smaller epinastic curvatures developed in both leaves and branches rotated at 15 minutes per revolution or more slowly. Indoleacetic acid-2-(14)C was used for measurements of extractable radioactivity in determining the reason for smaller curvatures of Coleus branches and tomato (Lycopersicon esculentum Mill.) leaves at the rotation rate of 60 minutes per revolution than at 1 minute per revolution. The cause was determined to be movement of some auxin from the upper into the lower side of a plagiotropic leaf or branch under the transient influence of gravity during rotation on the slower clinostat. A rotation period of 1 to 3 minutes was found to be acceptable for most plants.

Journal Article↗

PubMed2006

Leaf wetness duration measurement: comparison of cylindrical and flat plate sensors under different field conditions.

In general, leaf wetness duration (LWD) is a key parameter influencing plant disease epidemiology, since it provides the free water required by pathogens to infect foliar tissue. LWD is used as an input in many disease warning systems, which help growers to decide the best time to spray their crops against diseases. Since there is no observation standard either for sensor or exposure, LWD measurement is often problematic. To assess the performance of electronic sensors, LWD measurements obtained with painted cylindrical and flat plate sensors were compared under different field conditions in Elora, Ontario, Canada, and in Piracicaba, São Paulo, Brazil. The sensors were tested in four different crop environments--mowed turfgrass, maize, soybean, and tomatoes--during the summer of 2003 and 2004 in Elora and during the winter of 2005 in Piracicaba. Flat plate sensors were deployed facing north and at 45 degrees to horizontal, and cylindrical sensors were deployed horizontally. At the turfgrass site, both sensors were installed 30 cm above the ground, while at the crop fields, the sensors were installed at the top and inside the canopy (except for maize, with a sensor only at the top). Considering the flat plate sensor as a reference (Sentelhas et al. Operational exposure of leaf wetness sensors. Agric For Meteorol 126:59-72, 2004a), the results in the more humid climate at Elora showed that the cylindrical sensor overestimated LWD by 1.1-4.2 h, depending on the crop and canopy position. The main cause of the overestimation was the accumulation of big water drops along the bottom of the cylindrical sensors, which required much more energy and, consequently, time to evaporate. The overall difference between sensors when evaporating wetness formed during the night was around 1.6 h. Cylindrical sensors also detected wetness earlier than did flat plates--around 0.6 h. Agreement between plate and cylinder sensors was much better in the drier climate at Piracicaba. These results allow us to caution that cylindrical sensors may overestimate wetness for operational LWD measurements in humid climates and that the effect of other protocols for angling or positioning this sensor should be investigated for different crops.

Agriculture↗

PubMed1962

The grana of starch-free chloroplasts of Nicotiana rustica.

The grana of chloroplasts of starch-free leaves of Nicotiana rustica are described in detail. Leaf sections were fixed in 2.5 per cent KMnO(4) and embedded in mixtures of butyl and ethyl methacrylate. Chain length of the polymer was modified by use of a transfer agent. The grana are composed of compartments consisting of electron-scattering partitions and electron-transparent loculi. Compartments are not open to the stroma so that the grana are distinct subplastid organelles. Adjacent grana are connected by an anastomosing fretwork system composed of flexuous channels bordered by electron-scattering membranes. Ten different kinds of granum margins are described. These marginal variations depend upon grana-fretwork connections and internal marginal connections between adjacent loculi. A study of serial sections suggests, at least in some plastids, the occurrence of a possible orderly spiral arrangement of compartment-fretwork connections. Adjacent grana may have common compartments. Grana may branch. Variations in shape may depend upon the angle the section bears to the axis of the cylinder. This should also influence the relative thickness and sharpness of the partitions. Since all shapes and variations in partition thickness and sharpness cannot be accounted for on the basis of the orientation of the grana, such variations probably occur naturally. Grana vary in size, ranging from those few which have a single partition to those having 50 or more compartments which extend completely through the width of a plastid. Relationships between grana of different sizes and between compartments and frets indicate the possibility of growth of grana from union or extension of compartments and formation of compartments from the union of frets.

Chloroplasts↗

PubMed1988

Competency for graviresponse in the leaf-sheath pulvinus of Avena sativa: onset to loss.

The development of the leaf-sheath pulvinus of oat (Avena sativa L. cv. Victory) was studied in terms of its competency to respond to gravistimulation. Stages of onset of competency, maximum competency and loss of competency were identified, using the length of the supertending internode as a developmental marker. During the early phases in the onset of competency, the latency period between stimulus and graviresponse decreased and the steady state response rate increased significantly. When fully competent, the latency period remained constant as the plant continued to develop, suggesting that the latency period is relatively insensitive to quantitative changes (e.g., in carbohydrate or nutrient availability) at the cell level within the plant. In contrast, the response rate was found to increase with plant development, indicating that graviresponse rate is more strongly influenced by quantitative cellular changes. The total possible graviresponse of a single oat pulvinus was confirmed to be significantly less than the original presentation angle. This was shown to not result from a loss of competency, since the graviresponse could be reinitiated by increasing the presentation angle. As a result of the low overall graviresponse of individual pulvini, two or more pulvini are required to bring the plant apex to the vertical. This was determined to occur though the sequential, rather than simultaneous, action of successive pulvini, since a given pulvinus lost competency to gravirespond shortly after the next pulvinus became fully competent.

Avena↗

PubMed2001

[Physical-dosimetric characterization of a multi-leaf collimator system for clinical implementation in conformational radiotherapy].

INTRODUCTION: In the present paper we discuss the main dosimetric characteristics of the multileaf collimator (MLC) installed on the Elekta SLi Precise accelerators. To evaluate the effectiveness of the MLC in conformal radiotherapy, beam transmission through leaves and/or diaphragms, leakage between the leaves, central axis depth dose, surface dose, effective penumbra, scalopping effect and field size factors were measured. MATERIALS AND METHODS: The MLC installed on the dual energy (4 and 6 MV) linear accelerator Elekta SLi Precise consists of 40 opposed pairs of 75 mm thick tungsten leaves, set in two raws mounted in place of the upper collimator. Each leaf has a nominal projected width of 10 mm. The maximum field size attainable is 40 x 40 cm2 at 100 cm SAD. Beam transmission through leaves and/or diaphragms and field size factors were measured in RW3 phantom with a ionization chamber, leakage between the leaves and effective penumbra were instead evaluated with radiographic films (X-Omat-V) and a laser scanning photodensitometer. Percentage depth doses were measured in an automatic water phantom. RESULTS: For both energies, approximately 1% of the incident radiation on the multileaf collimator is transmitted through the backup collimator, while the transmission through the different combinations of leaves and collimators is between 0.03 and 0.14%. These values show a good agreement with literature data and are in general lower than the peak values specified by the manufacturer. The peak value of the leakage between the leaves was about 2% for both energies, without significative variation with gantry or collimator angle or distance from the axis. MLC shaped fields show a skin dose less (about 3%) than the one of cerrobend block shaped fields, because of the electronic contamination due to the plexiglass tray of the cerrobend blocks; in both cases, the depth doses are similar, as are flatness and symmetry of irradiation fields. The effective penumbra increases with field dimension, depth and leaves positioning, with a mean value of about 9 mm for both energies. The different beam configurations do not significantly affect the values of the field size factors. CONCLUSIONS: The dosimetric characteristics and the case of use of the Elekta multileaf collimator make its application to conformal radiotherapy convenient and reliable, able to improve the accuracy and the effectiveness of radiation therapy and to develop new kinds of treatments. However, because of the complexity of the MLC, its implementation in radiotherapic practice requires careful dosimetric characterization to evaluate those parameters (transmission, penumbra and output factors) that play a fundamental role in the accuracy of the treatment.

Equipment Design↗

PubMed1997

Structural studies of the glycine decarboxylase complex from pea leaf mitochondria.

The glycine decarboxylase complex consists of four different component enzymes (P-, H-, T- and L-proteins). The 14-kDa lipoamide-containing H-protein plays a pivotal role in the complete sequence of reactions since its prosthetic group (lipoic acid) interacts successively with the three other components of the complex and undergoes a cycle of reductive methylamination, methylamine transfer and electron transfer. The X-ray crystal structure of different forms of the H-protein has shown a unique conformation of the protein. This leads to the hypothesis of a three-dimensional recognition of the H-protein by the other components of the system and also by the ligase which lipoylates the H-protein. Striking structural similarities are observed between the H-protein and other lipoate domains of 2-oxo acid dehydrogenases and with the biotin carrier protein of acetyl-CoA carboxylase. In the H-protein, the lipoamide arm is free to move in the solvent when oxidized but is pivoted and tightly bound into a cleft at the protein surface when methylamine-loaded. This implies that the H-protein and the T-component form a stable complex during the catalytic transfer of the methylene unit to the tetrahydrofolate cofactor of the T-protein. This complex has been detected by small angle scattering experiments. In conclusion, in the glycine decarboxylase system, the lipoamide arm does not swing freely from one catalytic site to another as was proposed in other systems.

Amino Acid Oxidoreductases↗

PubMed2002

Spatial arrangement of branches in relation to slope and neighbourhood competition.

To gain a better understanding of the effects of spatial structure on patterns of neighbourhood competition among hardwood trees, the three-dimensional extension of primary branches was surveyed for ten community-grown Castanea crenata (Fagaceae) trees with respect to the positioning of neighbouring branches and the slope of the forest floor. There were significantly more branches extending towards the lower side of the slope than towards the upper side, but structural properties such as branch length and vertical angle were not affected by slope. When horizontal extension of a branch towards its neighbour was compared for a C. crenata branch and a neighbouring heterospecific, the former was significantly narrower than the latter when the inter-branch distance (horizontal distance between the base positions of two neighbouring branches) was short (< approx. 5 m). Castanea crenata branches tended to extend in a direction avoiding neighbouring branches of heterospecifics when the inter-branch distance was short. Furthermore, for an inter-branch distance <3 m, the horizontal extension of a C. crenata branch was less when it was neighbouring a heterospecific branch than when neighbouring a conspecific branch. These results suggest that horizontal extension of C. crenata branches is more prone to spatial invasion by nearby neighbouring branches of heterospecifics, and that the invasion can be lessened when C. crenata trees are spatially aggregated. The reason why such an arrangement occurs is discussed in relation to the later leaf-flush of C. crenata compared with that of other species in the forest.

Computer Simulation↗

PubMed2004

Quality assurance devices for dynamic conformal radiotherapy.

Two quality control devices, light-field device and radiation-field device, have been specially designed to facilitate the clinical implementation of conformal dynamic arc treatment (CDAT) and intensity modulated radiation therapy (IMRT). With the devices, the light field as well as the radiation field, projected from the individual beam at any treatment position (i.e. arbitrary gantry angle) can be evaluated. For application, the device was attached at the front end of the couch and was placed at the isocentre of the linear accelerator treatment system (LINAC). The devices are designed to be rotated parallel to the gantry head so that the light field and the radiation field projected from a direct beam can be assessed. The aim of the study is, with the aid of the devices, to evaluate the geometric precision of the beam placement and the dosimetric accuracy performed in CDAT and IMRT. The devices are placed separately from the LINAC during application and provide an independent check on the quality performance of the LINAC in three dimensions. The condition of gantry sag and any mechanical displacement resulting in field shift can be observed and traced during gantry rotation. Mistakes that occurred during the isocentre calibration can lead to significant displacement in the field projection, which would not be revealed with the conventional quality control setting (i.e. gantry 0(o)), was demonstrated with the aid of the devices here. The influence of gravitational acceleration in MLC leaf positioning error, which would consequently lead to inaccurate dose delivery, was investigated. The results of our study show that the existence of gravitational influence is statistically significant, although the magnitude of the dose inaccuracy has been found to be small.

Equipment Design↗

PubMed1997

Comparison of miniature multileaf collimation (MMLC) with circular collimation for stereotactic treatment.

PURPOSE: A prototype Miniature Multi-Leaf Collimator (MMLC) designed specifically for radiosurgery and small field radiotherapy has been fabricated and evaluated at the University of Texas M. D. Anderson Cancer Center (UTMDACC). This work demonstrates the advantages of a computer-controlled MMLC vs. conventional circular collimation for the treatment of an irregularly shaped target volume in the brain. METHODS AND MATERIALS: Two patient treatments were selected for this comparison from 38 intracranial tumors treated with radiosurgery at UTMDACC from 8/6/91 to 5/10/94. Target contours and critical structures defined for one of the patients was used to create a simulated target volume and critical structures in a spherical head phantom. Computer simulations were performed using traditional single isocenter treatment with a circular collimator for a set of six arcs. The same arc paths were used to compute the dose distribution for the MMLC and conformed beam geometries were defined using a three-dimensional (3D) treatment planning system with beam's eye view capabilities. Then, the calculated dose distribution for a single isocenter, conformal treatment was delivered to the spherical head phantom under static conditions by shaping the MMLC to conform the target volume shape projected as a function of couch rotation and gantry angle. Planar dose distributions through the target volume were measured using therapy verification film located in the phantom. The measurements were used to verify that the 3D treatment planning system was capable of simulating the MMLC technique. For the second patient with a peanut-shaped tumor, the 3D treatment planning calculations were used to compare dose distributions for the MMLC and for traditional single and multiple isocenter treatments using circular collimators. The resulting integral dose-volume histograms (DVHs) for the target volume, normal brain, and critical structures for the three treatment techniques were compared. RESULTS: (a) Analysis of the film dosimetry data exemplified the degree of conformation of the high-dose region to the target shape that is possible with a computer-controlled MMLC. (b) Comparison of measured and calculated dose distributions indicates that the 3D treatment planning system can simulate the MMLC treatment. (c) Comparison of DVHs from the single isocenter MMLC and circular collimator treatments shows similar coverage of the target volume with increased dose to the brain for circular collimation (4). Comparison of DVHs from the single isocenter MMLC with the multiple isocenter circular collimator treatment approach shows a more inhomogeneous dose distribution through the target volume and increased dose to the brain for the latter. CONCLUSION: Dosimetry data for single isocenter treatments using computer-controlled field shaping with a MMLC demonstrate the ability to conform the dose distribution to an irregularly shaped target volume. DVHs validated that the single isocenter MMLC treatment is preferable to both single and multiple isocenter, circular collimator treatment because it provides a more uniform dose distribution to an irregularly shaped target volume and reduces the dose to surrounding brain tissue for the example cases.

Adenocarcinoma↗

PubMed2004

[Difference in light acclimation mechanisms between light-loving and shade-tolerant ficus species].

The effects of light intensity on photosynthetic characteristics and possible mechanisms of preventing photodamage for two Ficus species seedlings grown under different irradiance were studied in rainy season. Ficus tinctoria Corner. is a sun species. Ficus subulata Bl. is a shade-tolerant species. With the increase of growth light intensity, maximum photosynthetic rate (P(max)), midrib angle (MA), chlorophyll a to b ratio (Chl a/b), carotenoid to chlorophyll ratio (Car/Chl), and thermal dissipation (NPQ) increased, while chlorophyll content and the amount of light harvesting complex of photosystem II decreased in both Ficus species. Those changes could reduce the existence of excessive light energy and ameliorated the extent of photoinhibition of photosynthesis. Under strong irradiance, photosynthetic rate was higher in F. tinctoria grown under 100% and 36% relative irradiance (RI) than in F. subulata, but their thermal dissipation capacity did not differ significantly. The results suggested that under strong irradiance seedlings could reduce excessive light energy through increasing both light energy utilization by photosynthesis and thermal dissipation in F. tinctoria, but through increasing thermal dissipation only in F. subulata. Reducing excessive light energy could protect photosynthetic apparatus from photoinhibition or photodamage. Under low irradiance, excessive light energy was reduced mainly through increasing light energy utilization by photosynthesis in F. tinctoria when grown under 100% and 36% RI and through increasing both photosynthetic utilization and thermal dissipation when grown under 12% and 4% RI, and through increasing thermal dissipation only in F. subulata. The extent of photoinhibition was greater in F. subulata than in F. tinctoria under the same irradiance of leaf surface, while the diurnal changes in photoinhibition was similar between the two species when grown under 100% RI. Under 100% RI, MA is larger in F. subulata than in F. tinctoria, which resulted in a lower leaf surface irradiance in F. subulata than in F. tinctoria. This was the main reason that the two Ficus species showed similar diurnal photoinhibition pattern under 100% RI. Acclimation of MA to irradiance was important to Ficus plants, especially to F. subulata.

Chlorophyll↗