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PubMed2003

Whole abdominopelvic radiotherapy (WAPRT) using intensity-modulated arc therapy (IMAT): first clinical experience.

PURPOSE: Whole abdominopelvic radiation therapy (WAPRT) is a treatment option in the palliation of patients with relapsed ovarian cancer. With conventional techniques, kidneys and liver are the dose- and homogeneity-limiting organs. We developed a planning strategy for intensity-modulated arc therapy (IMAT) and report on the treatment plans of the first 5 treated patients. METHODS AND MATERIALS: Five consecutive patients with histologically proven relapsed ovarian cancer were sent to our department for WAPRT. The target volumes and organs at risk (OAR) were delineated on 0.5-cm-thick CT slices. The clinical target volume (CTV) was defined as the total peritoneal cavity. CTV and kidneys were expanded with 0.5 cm. In a preset range of 8 degrees interspaced gantry angles, machine states were generated with an anatomy-based segmentation tool. Machine states of the same class were stratified in arcs. The optimization of IMAT was done in several steps, using a biophysical objective function. These steps included weight optimization of machine states, leaf position optimization adapted to meet the maximal leaf speed constraint, and planner-interactive optimization of the start and stop angles. The final control points (machine states plus associated cumulative monitor unit counts) were calculated using a collapsed cone convolution/superposition algorithm. For comparison, two conventional plans (CONV) were made, one with two fields (CONV2), and one with four fields (CONV4). In these CONV plans, dose to the kidneys was limited by cerrobend blocks. The IMAT and the CONV plans were normalized to a median dose of 33 Gy to the planning target volume (PTV). Monomer/polymer gel dosimetry was used to assess the dosimetric accuracy of the IMAT planning and delivery method. RESULTS: The median volume of the PTV was 8306 cc. The mean treatment delivery time over 4 patients was 13.8 min. A mean of 444 monitor units was needed for a fraction dose of 150 cGy. The fraction of the PTV volume receiving more than 90% of the prescribed dose (V(90)) was 9% higher for the IMAT plan than for the CONV4 plan (89.9% vs. 82.5%). Outside a build-up region of 0.8 cm and 1 cm away from both kidneys, the inhomogeneity in the PTV was 15.1% for the IMAT plans and 24.9% for the CONV4 plans (for CONV2 plans, this was 34.9%). The median dose to the kidneys in the IMAT plans was lower for all patients. The 95th percentile dose for the kidneys was significantly higher for the IMAT plans than for the CONV4 and CONV2 plans (28.2 Gy vs. 22.2 Gy and 22.6 Gy for left kidney, respectively). No relevant differences were found for liver. The gel-measured dose was within clinical planning constraints. CONCLUSION: IMAT was shown to be deliverable in an acceptable time slot and to produce dose distributions that are more homogeneous than those obtained with a CONV plan, with at least equal sparing of the OARs.

Adenocarcinoma↗

PubMed1979

Ratio of tree branch lengths: The equitable distribution of leaf clusters on branches.

The theoretical optimal ratios of branch lengths, which produce the most equitable distribution (minimum deviation) of leaf clusters in a computer-stimulated branch system, are similar to the observed ratios in real trees of Terminalia. In another study, observed values for branch angles in this species were shown to be similar to theoretical optimal values that produce the maximum effective leaf area. The relationship between these two fundamental parameters of bifurcation and tree geometry and their effect on effective leaf area and distribution of leaves are discussed.

Journal Article↗

PubMed2006

Physicochemical properties of functional surfaces in pitchers of the carnivorous plant Nepenthes alata Blanco (Nepenthaceae).

Pitchers of the carnivorous plant Nepenthes alata are highly specialized organs adapted to attract, capture, and digest animals, mostly insects. They consist of several well distinguishable zones, differing in macro-morphology, surface microstructure, and functions. Since physicochemical properties of these surfaces may influence insect adhesion, we measured contact angles of non-polar (diiodomethane) and polar liquids (water and ethylene glycol) and estimated the free surface energy of 1) the lid, 2) the peristome, 3) the waxy surface of the slippery zone, and 4) the glandular surface of the digestive zone in N. alata pitchers. As a control, the external surface of the pitcher, as well as abaxial and adaxial surfaces of the leaf blade, was measured. Both leaf surfaces, both lid surfaces, and the external pitcher surface showed similar contact angles and had rather high values of surface free energy with relatively high dispersion component. These surfaces are considered to support strong adhesion forces based on the capillary interaction, and by this, to promote successful attachment of insects. The waxy surface is almost unwettable, has extremely low surface energy, and therefore, must essentially decrease insect adhesion. Both the peristome and glandular surfaces are wetted readily with both non-polar and polar liquids and have very high surface energy with a predominating polar component. These properties result in the preclusion of insect adhesion due to the hydrophilic lubricating film covering the surfaces. The obtained results support field observations and laboratory experiments of previous authors that demonstrated the possible role of different pitcher surfaces in insect trapping and retention.

Animals↗

PubMed1995

Dosimetric evaluation of the conformation of the multileaf collimator to irregularly shaped fields.

PURPOSE: The goal of this study was to evaluate the dosimetric characteristics of geometric MLC prescription strategies and compare them to those of conventional shielding block. METHODS AND MATERIALS: Circular fields, square fields, and 12 irregular fields for patients with cancer of the head and neck, lung, and pelvis were included in this study. All fields were shaped using the MLC and conventional blocks. A geometric criterion was defined as the amount of area discrepancy between the MLC and the prescription outline. The "least area discrepancy" (LAD) of the MLC conformation was searched by selecting the collimator angle, meanwhile keeping a preselected position along the width of the leaf into the prescribed field. Five LAD conventions were studied. These included the LAD-0, LAD-1/3, LAD-1/2, and LAD-2/3 that inserted the leaves at the 0, 1/3, 1/2, and 2/3 of the leaf end into the prescription field, respectively. In addition, the LAD optimization was applied to the transecting (TRN) approach for leaf conformation that prescribed an equal area of overblocking and underblocking under each leaf. Film dosimetry was performed in a 20 cm polystyrene phantom at 10 cm depth 100 cm from source to axis distance (SAD) for both 6 and 18 MV photons with each of the above MLC conformations and conventional blocks. The field penumbra width, defined as the mean of the separation between the 20% and 80% isodose lines along the normal of the prescription field edge, was calculated using both the MLC and conventional block film dosimetry and compared. In a similar way, the d20 is defined as the mean separation between the 20% isodose line and the prescription field edge, and the d80 is defined as the mean separation between the 80% isodose line and the prescription field edge. RESULTS: The field penumbra width for all MLC conventions was approximately 2 mm larger than that of the conventional block. However, there was a larger variation of the separation distribution in the penumbra region of the irregular fields for the MLC, which had a standard deviation of 1 mm (a factor of 5 larger than the conventional block). The dosimetry for the circular fields showed that the LAD-TRN, LAD-1/2, and LAD-1/3 approximated the conventional blocking well in terms of d20 and d80; however, no single convention produced the best conformation for both measures. The dosimetric result of the patient treatment fields was similar for all sites. The LAD-1/3, LAD-1/2, and LAD-TRN strategies conformed to within 1 to 1.5 mm of the d80 of the conventional block for both 6 MV and 18 MV, respectively. The LAD-1/2 and LAD-TRN conformations were virtually identical, although it is proven analytically that the LAD-1/2 convention has the least overall area discrepancy of all conventions. CONCLUSIONS: The five MLC conformation conventions resulted in similar dosimetric penumbrae for all field shapes studied. The LAD-1/3, LAD-TRN, and LAD-1/2 produced the more favorable approximation to conventional block. The field penumbra width, although useful for evaluating irregular field shapes, could not describe the large local variations in the penumbra along the field edge for the MLC. These local variations could be of clinical concern when they appear near vital organs. However, the variation in a local region can potentially be reduced by minimizing the jaggedness of the leaf steps in that local region. The dosimetric results were useful as guidelines for the clinicians in the evaluation and adjustment of MLC leaf positions.

Head and Neck Neoplasms↗

PubMed2004

[Effects of grazing on architecture and small-scale pattern of grasses on artificial grassland in subtropical zone].

This study was conducted on a 5-year artificial grassland in subtropical zone of South China. The main types of established artificial grassland there were Dactylis glomerata-Lolium prenne-Trifolium repens and D. glomerata-T. repens pastures. Four grazing intensities were designed, i.e., CK (no grazing), G1 (6 adult sheep x hm(-2)), G2 (7.5 adult sheep x hm(-2)) and G3 (10 adult sheep x hm(-2)), and all the grazing plots were rotationally grazed. The architecture and small-scale pattern of grasses on the grazed and ungrazed grassland were discussed. After a period of 5-year grazing, the plant basal width and sward height of D. glomerata and T. pratense decreased gradually. In treatments CK, G1, G2 and G3, the basal width of D. glomerata was 6-8, 2-4, 0-2 and 0-2 cm, and that of T. pratense was 1-1.2, 6-8, 4-6 and 2-4 cm, respectively. The tuft density of D. glomerata in treatments CK, G1, G2 and G3 was 60, 95.1, 210.2 and 160 tufts x m(-2), respectively. The tiller number per plant of D. glomerata decreased, while its tuft density increased significantly due to the increased grazing intensity. With the increase of grazing intensity, the internode length of T. repens decreased, while its branching angle increased. The average internode length in treatments CK, G1, G2 and G3 was 2.04, 1.69, 1.64 and 1.51 cm, while the branching angle was 46.5, 65, 73 and 77.3 degrees, respectively. The average leaf density of T. repens in treatments CK, G1, G2 and G3 was 2.9, 13.0, 4.7 and 1.0 x m(-2), while the relevant stolon density was 19.9, 101, 142 and 82.6 m x m(-2), respectively. Under moderate grazing intensity, both the leaf and stolon densities of T. repens increased. The main scale on small pattern of D. glomerata, T. repens and T. pratense was 2 cm x 2 cm, which was further decreased under higher grazing intensity in the treatments of D. glomerata and T. pratense. Considering the heterogeneity of environmental resources, the change of the architecture and small-scale pattern could be regarded as an adaptation of grasses under grazing disturbance.

Animal Feed↗

PubMed1997

[The application of the multileaf collimator in radiotherapy: the dosimetric problems and the technical implications for its clinical use].

INTRODUCTION: The multileaf collimator (MLC) now commercially available as an integral or optional retrofit component of linear accelerator heads, permitting to shield automatically irregular fields by computerized movements of multiple tungsten leaves. In the present paper we discuss the main characteristics of different MLC versions, MLC dosimetric drawbacks and the clinical fields where the MLC could he widely used. MATERIALS AND METHODS: Since February, 1995, we have studied the dosimetric characteristics and clinical implications of a multileaf collimator of a Clinac 2100 C/D linear accelerator used to replace conventional low melting alloy blocks. The scalloping effect of isodoses and the effective penumbra produced by the multileaf collimator in an irregular field were analyzed accurately. Secondly, radiation leakage through tungsten leaves was measured and compared with the values of low melting alloy blocks. Finally, the MLC was extensively used in clinical practice for the radiotherapy of different tumors. RESULTS: Different dosimetric steps were followed to obtain the monitor units/dose ratio. Our single MLC-shielded irregular fields measurements also showed several physical and dosimetric disadvantages related to wider effective penumbra than with conventional shielding when the angle between field margin and the normal to the direction of leaf travel is 45 degrees. In clinical practice, the MLC can be widely used for the conformal radiotherapy of pelvic and thoracic tumors. Conventional low melting alloy blocks should be replaced with MLC for radiotherapy of selected brain and head and neck cancers. DISCUSSION: The current use of a multileaf collimator improves both the accuracy and the effectiveness of radiation therapy and reduces the time for every treatment dose, which potentially increases the number of patients treated every day. The multileaf collimator is presently an important technical tool either to replace conventional shielding for static conformational radiotherapy or to administer 3D-planned dynamic radiotherapy.

Equipment Design↗

PubMed1999

Interactions between senescence and leaf orientation determine in situ patterns of photosynthesis and photoinhibition in field-grown rice

Photosynthesis and photoinhibition in field-grown rice (Oryza sativa L.) were examined in relation to leaf age and orientation. Two varieties (IR72 and IR65598-112-2 [BSI206]) were grown in the field in the Philippines during the dry season under highly irrigated, well-fertilized conditions. Flag leaves were examined 60 and 100 d after transplanting. Because of the upright nature of 60-d-old rice leaves, patterns of photosynthesis were determined by solar movements: light falling on the exposed surface in the morning, a low incident angle of irradiance at midday, and light striking the opposite side of the leaf blade in the afternoon. There was an early morning burst of CO2 assimilation and high levels of saturation of photosystem II electron transfer as incident irradiance reached a maximum level. However, by midday the photochemical efficiency increased again almost to maximum. Leaves that were 100 d old possessed a more horizontal orientation and were found to suffer greater levels of photoinhibition than younger leaves, and this was accompanied by increases in the de-epoxidation state of the xanthophyll cycle. Older leaves had significantly lower chlorophyll content but only slightly diminished photosynthesis capacity.

Journal Article↗

PubMed1998

Design and characterization of a dynamic multileaf collimator.

The characteristics of a prototype computer-assisted dynamic multileaf collimator (DMLC), specifically designed for small-field conformal radiotherapy, were evaluated at the Istituto Nazionale Tumori of Milan. The collimating device consists of two opposing banks of 16 pairs of 8 cm thick, 3.6 mm wide tungsten leaves and allows shaping of a radiation field up to a size of 10 x 10 cm2 at the isocentre. The screening thickness of each leaf is 6.25 mm at the accelerator gantry isocentre. The leaves have a trapezoidal cross section and move along an arched path, thus providing a 'double focused' collimation system. The DMLC was installed on the head of a Varian Clinac 2100C linear accelerator. Mechanical and dosimetric evaluations were performed to test the stability of the mechanical isocentre and to determine leaf leakage, penumbra width, accuracy of leaf positions and uniformity of leaf speed. Displacement of the mechanical isocentre was less than 1 mm at all gantry angles. Standard radiographic films exposed to 6 MV x-ray radiation were used for dosimetric evaluations. Leakage between leaves was less than 2.5%, and leakage through abutted leaves was less than 5.5%. The penumbra width between 20% and 80% isodose at different positions of leaf banks was 2.7 mm in the direction of the leaf motion and 3.1 mm along the side of the leaf with a standard deviation of 0.2 mm in both directions. Accuracy in the positioning of the leaf was 0.3 mm, whereas the maximum repositioning error was less than 0.2 mm. Finally, during movement of the leaves at the maximum speed of 0.5 mm s(-1), the standard deviation of the leaf positioning error was 0.2 mm, proving an accurate uniformity of leaf speed.

Neoplasms↗

PubMed1998

Morphological and physiological markers of juvenility and maturity in shoot cultures of oak (Quercus robur and Q. petraea).

Evaluation of potential techniques for rejuvenating oak shoots requires robust quantitative markers for juvenile and mature plants. To identify suitable in vitro markers, shoot cultures of Quercus species of juvenile, adolescent and mature origin were screened for a range of morphological and physiological markers of juvenility and maturity. Criteria examined included angle of the shoot to the horizontal, stem length, stem diameter (tip, mid, base), leaf number, scale leaf number and shoot number. Image analysis was also carried out to determine leaf area, size, perimeter and breadth and length of leaves. Mature Q. robur L. clones had a larger mid-stem and tip diameter than juvenile clones, whereas mature Q. petraea ex Liebl. clones were characterized by plagiotropic growth and larger mid-stem and tip diameters compared with juvenile clones. Based on discriminant analysis of the data, we propose the following formulae for discrimination of juvenile and mature shoots, where a negative value for the discriminant score (D) indicates juvenility. For Q. petraea: D = -1.308 - 0.0351 SA + 2.206 TD + 1.435 MSD, where SA is stem angle ( degrees ), TD is tip diameter (mm) and MSD is mid-stem diameter (mm). For Q. robur: D = -3.546 + 2.418 TD + 2.202 MSD. Quercus robur clones derived from stump sprouts and designated as juvenile had a negative D value suggesting a juvenile status for these clones. Clones sourced from a hedged, grafted Q. robur tree of mature origin had a positive D value indicating a mature status. Clones initiated from a 20-25-year-old Q. petraea tree displayed morphology in vitro consistent with a mature status and had a positive D value; however, these clones displayed other traits such as vigor suggesting that vestiges of juvenility remain. Multiplication rate and leaf size and shape were variable among clones and did not provide suitable markers for juvenility or maturity for these Quercus species.

Journal Article↗

PubMed1996

Germination of Phyllosticta ampelicidaPycnidiospores: Prerequisite of Adhesion to the Substratum and the Relationship of Substratum Wettability

Pycnidiospores of Phyllosticta ampelicida, the causal agent of black rot of grape, were found to germinate only on substrata on which they were firmly attached. Such surfaces were poorly wettable and had advancing contact angles (straight thetaa) formed by a water drop of >80°, e.g., grape leaf, polystyrene, Teflon, polycarbonate, collodion, and glass treated with the silanes n-octadecyltrichlorosilane, dimethyldichlorosilane, or diphenyldichlorosilane. When pycnidiospores were deposited on more wettable surfaces they did not attach firmly and did not germinate. Such highly wettable surfaces had straight thetaa </= 40° and were represented by heat-treated glass, cellophane, nutrient- and water-agars, polystyrene treated with UV-irradiation or sulfuric acid, and glass silanized with n-2-aminoethyl-3-aminopropyltrimethoxysilane, n-(trimethoxysilylpropyl)ethylenediamine triacetic acid trisodium, or 3-aminopropyltriethoxysilane. Adhesion of pycnidiospores was assessed with and without a hydraulic shearing force. Pycnidiospore adhesion occurred over several minutes in distilled deionized water, unless it was first acidified, which decreased attachment time to <0.03 s. Attachment of pycnidiospores treated with sodium azide, formaldehyde, or boiled in water for 10 min was similar to nontreated conidia. Possible mechanisms of adhesion of the conidia to surfaces include hydrophobic and ionic interactions.

Journal Article↗

PubMed2002

Direct aperture optimization: a turnkey solution for step-and-shoot IMRT.

IMRT treatment plans for step-and-shoot delivery have traditionally been produced through the optimization of intensity distributions (or maps) for each beam angle. The optimization step is followed by the application of a leaf-sequencing algorithm that translates each intensity map into a set of deliverable aperture shapes. In this article, we introduce an automated planning system in which we bypass the traditional intensity optimization, and instead directly optimize the shapes and the weights of the apertures. We call this approach "direct aperture optimization." This technique allows the user to specify the maximum number of apertures per beam direction, and hence provides significant control over the complexity of the treatment delivery. This is possible because the machine dependent delivery constraints imposed by the MLC are enforced within the aperture optimization algorithm rather than in a separate leaf-sequencing step. The leaf settings and the aperture intensities are optimized simultaneously using a simulated annealing algorithm. We have tested direct aperture optimization on a variety of patient cases using the EGS4/BEAM Monte Carlo package for our dose calculation engine. The results demonstrate that direct aperture optimization can produce highly conformal step-and-shoot treatment plans using only three to five apertures per beam direction. As compared with traditional optimization strategies, our studies demonstrate that direct aperture optimization can result in a significant reduction in both the number of beam segments and the number of monitor units. Direct aperture optimization therefore produces highly efficient treatment deliveries that maintain the full dosimetric benefits of IMRT.

Algorithms↗

PubMed1985

[Biomechanical analysis of the medullary bone nail and its locking].

By mechanical definition an intramedullary nail is not a nail but rather a bendable feather, subject to longitudinal tension and to a lesser degree to transverse pressure. Reaming the medullary canal is necessary for centralization of the nail as well as to increase the area of contact with the bone. However, this procedure is detrimental to the bone metabolism and reduces its elasticity against torsional forces. The dynamic locking nail-system is more biologic than conventional nailing and it reduces rotatory instability with the help of additional components, such as transverse screws. Only static locking allows true static weight bearing with crutches, but not dynamic mobilisation. Nails with conventional strength and in leaf of trefoil formation are superior to other designs. However, an improved angle in the proximal locking is suggested, as this would allow for a three to four times greater weight bearing.

Biomechanical Phenomena↗

PubMed2005

Generation of wedge-shaped dose distributions through dynamic multileaf collimator dose delivery.

A new method of generating wedge-shaped dose distributions through dynamic multileaf collimator dose delivery rather than computer-controlled jaw motion is presented. The method starts with the calculation of a wedge-shaped beam profile for the desired wedge angle. The resultant wedge beam profile is then passed to the intensity-modulated radiation therapy (IMRT) leaf sequence generation algorithm to create multileaf collimator (MLC) segments for dose delivery. Wedge-shaped dose distributions are achieved through dynamic MLC dose delivery guided with the generated MLC segments. The method has been tested by generating wedgeshaped doses for a set of conventional wedge angles (i.e., 15 degrees, 30 degrees, 45 degrees, and 60 degrees). Film dosimetry is used for dose distribution verification. For each dose delivery guided with MLC segments created for the indicated wedge angle, the desired wedge-shaped dose distributions are observed. It is concluded that the dynamic MLC can be used to implement dynamic wedges in the clinic. This technique is different from the virtual wedge or the dynamic wedge developed for a particular type of LINAC. The same method can be applied to any machine equipped with a MLC. Other advantages are that it can generate a wedge field at an arbitrary orientation as the omni wedge does, and it creates wedged and shaped fields using a MLC only.

Dose Fractionation, Radiation↗

PubMed1996

Effect of phosphorus deficiency on growth angle of basal roots in Phaseolus vulgaris.

Root architectural plasticity might be an important factor in the acquisition by plants of immobile nutrients such as phosphorus (P). In this study, we examined the effect of P availability on the orientation of basal roots with respect to gravity, and thereby on the growth angle of these roots of common bean (Phaseolus vulgaris L.). In one set of studies the growth angle of basal roots of bean seedlings was measured over time. Sixteen bean genotypes were examined; six showed a decrease in root orientation with respect to gravity in low P media, one increased orientation, and nine showed no difference within 5 d of basal root emergence. Bean taproots also showed decreased root orientation with respect to gravity in low P. Growth angle after 5 d was correlated with field performance of contrasting genotypes in low P tropical soils. Mineral deficiencies other than P did not cause changes in root angle. In a split pouch system that provided high or low P solution to different parts of the root system, the decrease in root angle in low P was found to be a response to global P availability, and not local to the portion of the root system in low P. Effects of P availability on root angle were associated with reduced shoot P concentration, but preceded effects on plant biomass accumulation and leaf area expansion. Results from growth pouches for genotype G 19833 were confirmed using a solid-phase buffered sand-culture system supplying P at three levels. Pea (Pisum sativum), soybean (Glycine max Williams), chickpea (Cicer arietinum), lima bean (Phaseolus lunatus), and lentil (Lens culinaris) were grown with and without P; soybean and pea also showed decreased basal root angles in low P.

Biomass↗

PubMed2001

Intracanopy lighting reduces electrical energy utilization by closed cowpea stands.

The high planting densities needed to grow edible biomass in sustainable space life support systems will create problems for planophile crops that form closed, self-shading canopies. The use of traditional overhead-lighting configurations will reduce the penetration of photosynthetically active radiation (PAR) into such canopies and will result in substantial shading of understory leaves. Intracanopy lighting, an irradiation approach that allows plants to grow around fixed arrays of low-intensity lamps, reduces overall energy expenditure for crop production by improving light distribution and interception throughout the canopy. Comparing different fluorescent lamp geometries within vegetative canopies of cowpea (Vigna unguiculata L. Walp) revealed great plasticity of leaf orientation to maximize absorption of PAR from lamps arrayed at various nontraditional angles. Varying the amount of photosynthetic energy available within canopies creates considerable potential to manipulate canopy productivity. Increasing lamp number 38% within cowpea canopies raised stand productivity 45%, reflecting the highly efficient interception and absorption of intracanopy PAR. However, combined above/within-canopy lighting did not increase overall PAR interception and vegetative yield, and productivity did not improve relative to the same input wattage of intracanopy lighting alone. Optimization of intracanopy lighting for crops to be used in future space life support systems will substantially reduce power and energy burdens for food-crop production.

Biomass↗

PubMed1989

Effect of Surface-Active Pseudomonas spp. on Leaf Wettability.

Different strains of Pseudomonas putida and P. fluorescens isolated from the rhizosphere and phyllosphere were tested for surface activity in droplet cultures on polystyrene. Droplets of 6 of the 12 wild types tested spread over the surface during incubation, and these strains were considered surface active; strains not showing this reaction were considered non-surface active. Similar reactions were observed on pieces of wheat leaves. Supernatants from centrifuged broth cultures behaved like droplets of suspensions in broth; exposure to 100 degrees C destroyed the activity. Average contact angles of the supernatants of surface-active and non-surface-active strains on polystyrene were 24 degrees and 72 degrees , respectively. The minimal surface tension of supernatants of the surface-active strains was about 46 mN/m, whereas that of the non-surface-active strains was 64 mN/m (estimations from Zisman plots). After 6 days of incubation, wheat flag leaves sprayed with a dilute suspension of a surface-active strain of P. putida (WCS 358RR) showed a significant increase in leaf wettability, which was determined by contact angle measurements. Increasing the initial concentration of bacteria and the amount of nutrients in the inoculum sprayed on leaves reduced the contact angles from 138 degrees on leaves treated with antibiotics (control) to 43 degrees on leaves treated with surface-active bacteria. A closely related strain with no surface activity on polystyrene did not affect leaf wettability, although it was present in densities similar to those of the surface-active strain. Nutrients alone could occasionally also increase leaf wettability, apparently by stimulating naturally occurring surface-active bacteria. When estimating densities of Pseudomonas spp. underneath droplets with low contact angles, it appeared that populations on leaves treated with a surface-active strain could vary from about 10 to 10 CFU cm, suggesting that the surface effect may be prolonged after a decline of the population. The possible ecological implications are discussed.

Journal Article↗

PubMed2003

Plant movement. Submergence-induced petiole elongation in Rumex palustris depends on hyponastic growth.

The submergence-tolerant species Rumex palustris (Sm.) responds to complete submergence by an increase in petiole angle with the horizontal. This hyponastic growth, in combination with stimulated elongation of the petiole, can bring the leaf tips above the water surface, thus restoring gas exchange and enabling survival. Using a computerized digital camera set-up the kinetics of this hyponastic petiole movement and stimulated petiole elongation were studied. The hyponastic growth is a relatively rapid process that starts after a lag phase of 1.5 to 3 h and is completed after 6 to 7 h. The kinetics of hyponastic growth depend on the initial angle of the petiole at the time of submergence, a factor showing considerable seasonal variation. For example, lower petiole angles at the time of submergence result in a shorter lag phase for hyponastic growth. This dependency of the hyponastic growth kinetics can be mimicked by experimentally manipulating the petiole angle at the time of submergence. Stimulated petiole elongation in response to complete submergence also shows kinetics that are dependent on the petiole angle at the time of submergence, with lower initial petiole angles resulting in a longer lag phase for petiole elongation. Angle manipulation experiments show that stimulated petiole elongation can only start when the petiole has reached an angle of 40 degrees to 50 degrees. The petiole can reach this "critical angle" for stimulated petiole elongation by the process of hyponastic growth. This research shows a functional dependency of one response to submergence in R. palustris (stimulated petiole elongation) on another response (hyponastic petiole growth), because petiole elongation can only contribute to the leaf reaching the water surface when the petiole has a more or less upright position.

Adaptation, Physiological↗

PubMed1976

Lunarperiodic variation of the phase-angle difference in nocturnal animals under natural Zeitgeber-conditions near the equator.

Several months' studies under natural illumination conditions in the vicinity of the equator show that night monkeys (Aotus trivirgatus), and leaf-nosed bats (Artibeus lituratus) exhibit species-specific lunarperiodic changes of the phase position of their activity rhythm to the Zeitgeber rhythm (Figures 1-3). These changes are closely to nightly illumination conditions. In Aotus the phase-angle differences (p.a.ds) of the onset and end of the activity phase, and in Artibeus the p.a.ds of the midpoint and end of the activity phase are significantly dependent upon the phases of the moon. In the African fruit bat Rousettus aegyptiacus, and in the leaf-nosed bat Phyllostomus hastatus no statistically significant lunarperiodic changes of the p.a.ds could be detected. These results cannot be explained by means of current models concerning the mechanism of synchronisation of biological oscillation. They appear to be, instead, expressions of a periodic masking of the real phase-position due to direct effects of light intensity on the level of activity which which itself is determined by the circadian rhythm. Aschoff's rule, which states that the earlier a species or an individual awakes the later it terminates its daily phase of activity, is partly confirmed for the nocturnal mammals examined in the present study.

Animals↗