Leaf Movement Research Articles

Modulation of ethylene- and heat-controlled hyponastic leaf movement in Arabidopsis thaliana by the plant defence hormones jasmonate and salicylate

Upward leaf movement (hyponastic growth) is adopted by several plant species including Arabidopsis thaliana, as a mechanism to escape adverse growth conditions. Among the signals that trigger hyponastic growth are, the gaseous hormone ethylene, low light intensities, and supra-optimal temperatures (heat). Recent studies indicated that the defence-related phytohormones jasmonic acid (JA) and salicylic acid (SA) synthesized by the plant upon biotic infestation repress low light-induced hyponastic growth. The hyponastic growth response induced by high temperature (heat) treatment and upon application of the gaseous hormone ethylene is highly similar to the response induced by low light. To test if these environmental signals induce hyponastic growth via parallel pathways or converge downstream, we studied here the roles of Methyl-JA (MeJA) and SA on ethylene- and heat-induced hyponastic growth. For this, we used a time-lapse camera setup. Our study includes pharmacological application of MeJA and SA and biological infestation using the JA-inducing caterpillar Pieris rapae as well as mutants lacking JA or SA signalling components. The data demonstrate that MeJA is a positive, and SA, a negative regulator of ethylene-induced hyponastic growth and that both hormones repress the response to heat. Taking previous studies into account, we conclude that SA is the first among many tested components which is repressing hyponastic growth under all tested inductive environmental stimuli. However, since MeJA is a positive regulator of ethylene-induced hyponastic growth and is inhibiting low light- and heat-induced leaf movement, we conclude that defence hormones control hyponastic growth by affecting stimulus-specific signalling pathways.

Gone with the wind: trembling leaves may deter herbivory

Plants employ various defensive tactics against herbivores but are rarely considered to use rapid movements to resist predation. However, the aboveground parts of plants are often forcefully moved by wind and rain. This passive movement has been overlooked as an anti-herbivore trait. The leaves of many plant species, such as aspens, Indian sacred fig, bamboos, and palms, tremble even in a slight breeze. Leaves that are easily moved by gentle winds can sometimes resist strong winds and may have other benefits as well. In the present study, it is proposed that the movement of such plant leaves physically deters arthropod herbivory and pathogen infection by repelling colonization and oviposition by herbivorous insects. This leads to herbivores and pathogens being dislodged from the plants, and the ensuing death of the herbivores on the ground or at least their recolonization to other plants, as well as the interruption of feeding, intraspecific communication and the mating behaviour of herbivores, thus lowering their performance on the plant or increasing enemy attack of the herbivores. In addition, passive leaf movements may undermine herbivore camouflage and expose them to predation, and may also allow plant volatiles to diffuse efficiently to repel herbivores and attract natural enemies. Thus, the mechanistic properties of these leaves may have anti-herbivore effects in the wind and rain. This hypothesis can also be applied to aquatic plants that tremble in gentle water currents. In addition, genetic manipulation of the tendency for leaf movement may be beneficial for the management of pest insects and pathogens with reduced pesticides in forestry and agriculture. © 2011 The Linnean Society of London, Biological Journal of the Linnean Society, 2011, 104, 738–747.

Ground-level ozone influenced by circadian control of isoprene emissions

The volatile organic compound isoprene is produced by many plant species, and provides protection against biotic and abiotic stresses 1 . Globally, isoprene emissions from plants are estimated to far exceed anthropogenic emissions of volatile organic compounds 2 . Once in the atmosphere, isoprene reacts rapidly with hydroxyl radicals 3 to form peroxy radicals, which can react with nitrogen oxides to form ground-level ozone 4 . Here, we use canopy-scale measurements of isoprene fluxes from two tropical ecosystems in Malaysia—a rainforest and an oil palm plantation—and three models of atmospheric chemistry to explore the effects of isoprene fluxes on ground-level ozone. We show that isoprene emissions in these ecosystems are under circadian control on the canopy scale, particularly in the oil palm plantation. As a result, these ecosystems emit less isoprene than present emissions models predict. Using local-, regional- and global-scale models of atmospheric chemistry and transport, we show that accounting for circadian control of isoprene emissions brings model predictions of ground-level ozone into better agreement with measurements, especially in isoprene-sensitive regions of the world. Circadian rhythms are common in nature, controlling such processes as body temperature and sleep patterns in animals and leaf movement and stomatal aperture in plants. Circadian clocks have been shown to confer a competitive advantage in plants: those with a circadian clock period matched to the external lightdark cycle contain more chlorophyll, fix more carbon, grow faster, have stronger defences and survive better than plants with circadian periodsdifferingfromtheirenvironment 5,6 .Despitetheimportance of circadian rhythms to plant physiology, circadian control has not previously been observed at the forest-canopy or landscape scales and so has not yet been built into our understanding of landatmosphere

Circadian rhythm leaf movement of Phaseolus vulgaris and the role of calcium ions

Legume plants, due to their distinctive botanical characteristics, such as leaf movements, physiological characteristics, such as nitrogen fixation, and their abilities to endure environmental stresses, have important roles in sustainable pastures development. Leaf movement of legume plants is turgor regulated, and osmotically active fluxes of ions between extensor and flexor of pulvinus cause this movement. To determine the role of calcium ions in circadian leaf movements of Phaseolus vulgaris L., a radiotracer technique experiment using 45Ca ions were employed. Measurements were taken during circadian leaf movements, and samples were taken from different parts of the leaflet. The 45Ca beta-particle activity reduced from leaflet base pulvinus to leaf tip. The pulvinus had the highest activity, while the leaf tip had the lowest. By increase of the ratio of 45Ca beta-particle activity within flexor to extensor (Fl/Ex) the midrib-petiole angle, as an indicator of leaf movement, increased linearly during circadian leaf movement (r = 0.86). The 45Ca beta-particle activity of Flex/Ext ratio reduced linearly (r = - 0.88) toward midnight. In conclusion, it was found that calcium ions accumulation is opposite to the fluxes of somatically active ions and water movement. Calcium ions accumulate at less negative water potential side of the pulivnus.

SU‐E‐T‐24: Remote, Automated Daily Delivery Verification of Volumetric Modulated Arc Therapy Treatments Using a Commercial Record and Verify System

Purpose: Volumetric modulated arc therapy (VMAT) is an effective but complex technique for delivering radiation therapy. VMAT relies on precise combinations of dose rate, gantry speed, and multi‐leaf collimator (MLC) shapes to deliver intensity modulated patterns. Such complexity warrants the development of correspondingly robust performance verification systems. In this work, we report on the feasibility of using data collected from a commercial record and verify system to perform remote, automated daily delivery verification of volumetric modulated arc therapy (VMAT) treatments. Methods: The performance verification software system consists of 3 main components: (1) a query module to retrieve daily MLC, gantry, and jaw positions reported by the linear accelerator control system (Elekta, Crawley, UK) to the record and verify system (Mosaiq, Elekta, Mountain View, CA, USA), (2) an analysis module to read the daily delivery report generated from the database query module, compare the reported treatment positions against the planned positions, and compile delivery position error reports, and (3) a reporting module to display graphical reports initiated by a user or to automatically alert authorized users when pre‐defined tolerance values are exceeded. The utility of the system was investigated through analysis of patient data collected at our clinic. Results: Nearly 2,500 VMAT fractions have been analyzed with the delivery verification system at our institution. The average percentage of reported MLC leaf positions within 3 mm, gantry positions within 2 degrees and jaw positions within 3 mm of their planned positions was 92.9 +/− 5.5%, 95.9 +/− 2.9%, and 99.7 +/− 0.6%, respectively. The level of agreement between planned and reported MLC positions decreased for treatment plans requiring larger MLC leaf movements between control points. Conclusions: The delivery verification system holds the potential to provide an effective and low‐cost quality assurance tool that improves patient safety.

Independent quality assurance of a helical tomotherapy machine using the dose magnifying glass

Helical tomotherapy is a complex delivery technique, integrating CT image guidance and intensity modulated radiotherapy in a single system. The integration of the CT detector ring on the gantry not only allows patient position verification but is also often used to perform various QA procedures. This convenience lacks the rigor of a machine-independent QA process. In this article, a Si strip detector, known as the Dose Magnifying Glass (DMG), was used to perform machine-independent QA measurements of the multileaf collimator alignment, leaf open time threshold, and leaf fluence output factor (LFOF). The DMG measurements showed good agreements with EDR2 film for the MLC alignment test while the CT detector agrees well with DMG measurements for leaf open time threshold and LFOF measurements. The leaf open time threshold was found to be approximately 20 ms. The LFOF measured with the DMG agreed within error with the CT detector measured LFOF. The DMG with its 0.2 mm spatial resolution coupled to TERA ASIC allowed real-time high temporal resolution measurements of the tomotherapy leaf movement. In conclusion, DMG was shown to be a suitable tool for machine-independent QA of a tomotherapy unit.

A genetic screen for leaf movement mutants identifies a potential role for AGAMOUS-LIKE 6 (AGL6) in circadian-clock control.

The circadian clock in plants regulates many important physiological and biological processes, including leaf movement. We have used an imaging system to genetically screen Arabidopsis seedlings for altered leaf movement with the aim of identifying a circadian clock gene. A total of 285 genes were selected from publicly available microarrays that showed an expression pattern similar to those of the Arabidopsis core oscillator genes. We subsequently isolated 42 homozygous recessive mutants and analyzed their leaf movements. We also analyzed leaf movements of activation tagging mutants that showed altered flowering time. We found that agl6-1D plants, in which AGAMOUS-LIKE 6 (AGL6) was activated by the 35S enhancer, showed a shortened period of leaf movement as well as a high level of ZEITLUPE (ZTL) expression, reduced amplitude of LATE ELONGATED HYPOCOTYL (LHY) expression, and arrhythmic TIMING OF CAB EXPRESSION1 (TOC1)/CIRCADIAN CLOCK ASSOCIATED1 (CCA1) expression. A shortened period of leaf movement was also seen in 35S-AGL6-myc plants, although 35S-amiRAGL6 plants, transgenic plants overexpressing an artificial miRNA (amiR) targeting AGL6, showed unaltered leaf movement. The amplitude of CHLOROPHYLL A/B BINDING PROTEIN 2 (CAB2) expression, a circadian output gene, was also reduced in agl6-1D plants. Taken together, these results suggest that AGL6 plays a potential role in the regulation of the circadian clock by regulating ZTL mRNA level in Arabidopsis.

On the mechanism underlying photosynthetic limitation upon trigger hair irritation in the carnivorous plant Venus flytrap (Dionaea muscipula Ellis).

Mechanical stimulation of trigger hairs on the adaxial surface of the trap of Dionaea muscipula leads to the generation of action potentials and to rapid leaf movement. After rapid closure secures the prey, the struggle against the trigger hairs results in generation of further action potentials which inhibit photosynthesis. A detailed analysis of chlorophyll a fluorescence kinetics and gas exchange measurements in response to generation of action potentials in irritated D. muscipula traps was used to determine the ‘site effect’ of the electrical signal-induced inhibition of photosynthesis. Irritation of trigger hairs and subsequent generation of action potentials resulted in a decrease in the effective photochemical quantum yield of photosystem II (ΦPSII) and the rate of net photosynthesis (AN). During the first seconds of irritation, increased excitation pressure in photosystem II (PSII) was the major contributor to the decreased ΦPSII. Within ∼1 min, non-photochemical quenching (NPQ) released the excitation pressure at PSII. Measurements of the fast chlorophyll a fluorescence transient (O-J-I-P) revealed a direct impact of action potentials on the charge separation–recombination reactions in PSII, although the effect seems to be small rather than substantial. All the data presented here indicate that the main primary target of the electrical signal-induced inhibition of photosynthesis is the dark reaction, whereas the inhibition of electron transport is only a consequence of reduced carboxylation efficiency. In addition, the study also provides valuable data confirming the hypothesis that chlorophyll a fluorescence is under electrochemical control.

12-Hydroxyjasmonic Acid Glucoside Is a COI1-JAZ-Independent Activator of Leaf-Closing Movement in Samanea saman

Jasmonates are ubiquitously occurring plant growth regulators with high structural diversity that mediate numerous developmental processes and stress responses. We have recently identified 12-O-β-D-glucopyranosyljasmonic acid as the bioactive metabolite, leaf-closing factor (LCF), which induced nyctinastic leaf closure of Samanea saman. We demonstrate that leaf closure of isolated Samanea pinnae is induced upon stereospecific recognition of (-)-LCF, but not by its enantiomer, (+)-ent-LCF, and that the nonglucosylated derivative, (-)-12-hydroxyjasmonic acid also displays weak activity. Similarly, rapid and cell type-specific shrinkage of extensor motor cell protoplasts was selectively initiated upon treatment with (-)-LCF, whereas flexor motor cell protoplasts did not respond. In these bioassays related to leaf movement, all other jasmonates tested were inactive, including jasmonic acid (JA) and the potent derivates JA-isoleucine and coronatine. By contrast, (-)-LCF and (-)-12-hydroxyjasmonic acid were completely inactive with respect to activation of typical JA responses, such as induction of JA-responsive genes LOX2 and OPCL1 in Arabidopsis (Arabidopsis thaliana) or accumulation of plant volatile organic compounds in S. saman and lima bean (Phaseolus lunatus), generally considered to be mediated by JA-isoleucine in a COI1-dependent fashion. Furthermore, application of selective inhibitors indicated that leaf movement in S. saman is mediated by rapid potassium fluxes initiated by opening of potassium-permeable channels. Collectively, our data point to the existence of at least two separate JA signaling pathways in S. saman and that 12-O-β-D-glucopyranosyljasmonic acid exerts its leaf-closing activity through a mechanism independent of the COI1-JAZ module.

Two distinct strategies of cotton and soybean differing in leaf movement to perform photosynthesis under drought in the field.

This paper reports an experimental test of the hypothesis that cotton and soybean differing in leaf movement have distinct strategies to perform photosynthesis under drought. Cotton and soybean were exposed to two water regimes: drought stressed and well watered. Drought-stressed cotton and soybean had lower maximum CO2 assimilation rates than well-watered (control) plants. Drought reduced the light saturation point and photorespiration of both species - especially in soybean. Area-based leaf nitrogen decreased in drought-stressed soybean but increased in drought-stressed cotton. Drought decreased PSII quantum yield (ΦPSII) in soybean leaves, but increased ΦPSII in cotton leaves. Drought induced an increase in light absorbed by the PSII antennae that is dissipated thermally via ΔpH- and xanthophylls-regulated processes in soybean leaves, but a decrease in cotton leaves. Soybean leaves appeared to have greater cyclic electron flow (CEF) around PSI than cotton leaves and drought further increased CEF in soybean leaves. In contrast, CEF slightly decreased in cotton under drought. These results suggest that the difference in leaf movement between cotton and soybean leaves gives rise to different strategies to perform photosynthesis and to contrasting photoprotective mechanisms for utilisation or dissipation of excess light energy. We suggest that soybean preferentially uses light-regulated non-photochemical energy dissipation, which may have been enhanced by the higher CEF in drought-stressed leaves. In contrast, cotton appears to rely on enhanced electron transport flux for light energy utilisation under drought, for example, in enhanced nitrogen assimilation.

マイクロマルチリーフコリメータを用いた定位放射線照射システムの機械的精度評価

Mechanical accuracy of a stereotactic irradiation system using a micro multi-leaf collimator (mMLC), Elekta DMLC, has been evaluated. Measurements were made to obtain transmission, leakage, penumbra, and positioning accuracy of the DMLC leaf for a 6 MV photon beam. Mechanical accuracy and long term stability of a linac isocenter was also evaluated. The resulting transmission, along a line perpendicular to the leaf movement, was 0.31±0.01%, and the leakage from the closed opposing leaf pairs was 0.39±0.01%. The measured penumbra, at a depth incurring maximum dose, was 2.37±0.16 mm toward the leaf end and 2.14±0.18 mm toward the leaf side for various field sizes. The leaf gap width error, of 0.10±0.08 mm, was obtained by analyzing picket fence test results. The maximum leaf positioning error, of 0.14±0.06 mm, was obtained by analyzing the log file for a various gantry angles during an arc delivery. The isocenter accuracy was within a radius of 1 mm, without any recalibration for two years. In conclusion, our stereotactic irradiation system using DMLC was capable of providing accurate stereotactic treatment.

Kinome Profiling Reveals an Interaction Between Jasmonate, Salicylate and Light Control of Hyponastic Petiole Growth in Arabidopsis thaliana

Plants defend themselves against infection by biotic attackers by producing distinct phytohormones. Especially jasmonic acid (JA) and salicylic acid (SA) are well known defense-inducing hormones. Here, the effects of MeJA and SA on the Arabidopsis thaliana kinome were monitored using PepChip arrays containing kinase substrate peptides to analyze posttranslational interactions in MeJA and SA signaling pathways and to test if kinome profiling can provide leads to predict posttranslational events in plant signaling. MeJA and SA mediate differential phosphorylation of substrates for many kinase families. Also some plant specific substrates were differentially phosphorylated, including peptides derived from Phytochrome A, and Photosystem II D protein. This indicates that MeJA and SA mediate cross-talk between defense signaling and light responses. We tested the predicted effects of MeJA and SA using light-mediated upward leaf movement (differential petiole growth also called hyponastic growth). We found that MeJA, infestation by the JA-inducing insect herbivore Pieris rapae, and SA suppressed low light-induced hyponastic growth. MeJA and SA acted in a synergistic fashion via two (partially) divergent signaling routes. This work demonstrates that kinome profiling using PepChip arrays can be a valuable complementary ∼omics tool to give directions towards predicting behavior of organisms after a given stimulus and can be used to obtain leads for physiological relevant phenomena in planta.

On the Relevance and Control of Leaf Angle

Plants can have constitutive leaf angles that are fixed and do not vary much among different growth environments. Several species, however, have the ability to actively adjust their leaf angles. Active leaf repositioning can be functional in avoiding detrimental environmental conditions, such as avoidance of heat stress and complete submergence, or can be, for example, utilized to maximize carbon gain by positioning the leaves relative to the incoming radiation. In recent years, major advances have been made in the understanding of the molecular mechanisms, and the underlying hormonal regulation of a particular type of leaf movement: hyponastic growth. This differential petiole growth-driven upward leaf movement is now relatively well understood in model systems such as Rumex palustris and Arabidopsis thaliana. In the first part of this review we will discuss the functional consequences of leaf orientation for plant performance. Next, we will consider hyponastic growth and describe how exploitation of natural (genetic) variation can be instrumental in studying the relevance and control of leaf positioning.

Genetic mapping of natural variation in a shade avoidance response: ELF3 is the candidate gene for a QTL in hypocotyl growth regulation

When plants become shaded by neighbouring plants, they perceive a decrease in the red/far-red (R/FR) ratio of the light environment, which provides an early and unambiguous warning of the presence of competing vegetation. The mechanistic bases of the natural genetic variation in response to shade signals remain largely unknown. This study demonstrates that a wide range of genetic variation for hypocotyl elongation in response to an FR pulse at the end of day (EOD), a light signal that simulates natural shade, exists between Arabidopsis accessions. A quantitative trait locus (QTL) mapping analysis was done in the Bayreuth×Shahdara recombinant inbred line population. EODINDEX1 is the most significant QTL identified in response to EOD. The Shahdara alleles at EODINDEX1 caused a reduced response to shade as a consequence of an impaired hypocotyl inhibition under white light, and an accelerated leaf movement rhythm, which correlated positively with the pattern of circadian expression of clock genes such as PRR7 and PRR9. Genetic and quantitative complementation analyses demonstrated that ELF3 is the most likely candidate gene underlying natural variation at EODINDEX1. In conclusion, ELF3 is proposed as a component of the shade avoidance signalling pathway responsible for the phenotypic differences between Arabidopsis populations in relation to adaptation in a changing light environment.

ChemInform Abstract: Chemistry and Biology of Plant Leaf Movements

The leaves of Mimosa pudica L. are well known for their rapid movement when touched. Recently, we were able to isolate an excitatory substance in small quantities from this plant, which consists of three different components (potassium L-malate, magnesium trans-aconitate, and dimethylammonium salt). Many plants close their leaves in the evening, as if to sleep, and open them early in the morning (nyctinastic leaf movement). This circadian rhythm is known to be controlled by the biological clock of such plants. Extensive studies on other nyctinastic plants led to the isolation of a variety of leaf-opening substances (LOSs) and leaf-closing substances (LCSs). Based on our experiments on these bioactive substances, we found that the circadian rhythmic leaf movement of these plants is initiated by the regulated balance of LOSs and LCSs. The balance of concentration between the two leaf-movement factors (LMFs) is inversed during the day. The glycoside-type LMF is hydrolyzed with β-glucosidase, the activity of which is regulated by the biological clock. The circadian rhythm observed in the leaf movement is introduced by activation of β-glucosidase regulated by the biological clock.

SU‐GG‐J‐85: A Method Incorporating 4DCT Data for Evaluating the Dosimetric Effects of Respiratory Motion in Single Arc IMAT

Purpose: The purpose of this work was to introduce a method to investigate the effect of the breathing motion in a single arc IMAT. We also investigated the role of plan complexity on the dosimetric impact of the respiratory motion in the delivery of VMAT. Method and Materials: The patient's motion model was built from deformable registration over 4DCT images. IMAT plans (one moderately modulated, another highly modulated) were partitioned into 10 (skip & shoot arc) sub‐plans, which were delivered to each of 10 corresponding CT phase image. The dose distribution was re‐warped with a deformation map into a reference phase CT image. The organ dose was derived from the weighted sum over all of the phases. Results: The moderately modulated plan had an average leaf movement of 386 mm and mean leaf gap of 37.9 mm. The highly modulated plan had a maximum leaf movement of 625 mm and leaf gap of 17.2 mm For a patient with a maximum motion displacement of ∼15 mm, the dosimetric impact is rather small and can be ignored for both of moderately and highly modulated IMAT, irrespective of number of fractions. Specifically, highly modulated plans only increased the degradation of D95 of the DVH curves for a single fraction by 2% in the CTV and 9% in the PTV compared to the mean value from a 25 fraction plan. Conclusion: Although single Arc IMAT has less flexible intensity modulation per beam direction, in the treatment of the lesion within the throax‐ abdominal site, less interplay between the organ motion and the dynamic movement gave it an advantage over the conventional IMRT techniques.

Altered physiological function, not structure, drives increased radiation-use efficiency of soybean grown at elevated CO2

Previous studies of elevated carbon dioxide concentration ([CO(2)]) on crop canopies have found that radiation-use efficiency is increased more than radiation-interception efficiency. It is assumed that increased radiation-use efficiency is due to changes in leaf-level physiology; however, canopy structure can affect radiation-use efficiency if leaves are displayed in a manner that optimizes their physiological capacity, even though the canopy intercepts the same amount of light. In order to determine the contributions of physiology and canopy structure to radiation-use and radiation-interception efficiency, this study relates leaf-level physiology and leaf display to photosynthetic rate of the outer canopy. We used a new imaging approach that delivers three-dimensional maps of the outer canopy during the growing season. The 3D data were used to model leaf orientation and mean photosynthetic electron transport of the outer canopy to show that leaf orientation changes did not contribute to increased radiation-use; i.e. leaves of the outer canopy showed similar diurnal leaf movements and leaf orientation in both treatments. Elevated [CO(2)] resulted in an increased maximum electron transport rate (ETR(max)) of light reactions of photosynthesis. Modeling of canopy light interception showed that stimulated leaf-level electron transport at elevated [CO(2)], and not alterations in leaf orientation, was associated with stimulated radiation-use efficiency and biomass production in elevated [CO(2)]. This study provides proof of concept of methodology to quantify structure-function relationships in combination, allowing a quantitative estimate of the contribution of both effects to canopy energy conversion under elevated [CO(2)].

Physical characterization and comparison of two commercially available micro-MLCs

In this study, the physical characteristics (penumbra width variation with the source size and shape, interleaf leakage, transmission through the leaves, and the tongue-and-groove effect) of two linear accelerators (BrainLAB's Novalis and Elekta's Synergy-S Beam Modulator) have been investigated. For similar square fields (about 4.5 cm × 4.5 cm) with source-to-surface/skin-distance (SSD) ranging from 90 cm to 115 cm and measurements taken at the depth of D max = 1.5 cm for 6 MV photon beam. The Novalis MLC has penumbra width of 2.4 ± 0.11 mm–2.8 ± 0.11 mm at the leaf-end and 2.2 ± 0.1 mm–2.7 ± 0.1 mm on the leaf-side; and those for the Synergy-S MLC are 4.4 ± 0.17 mm–5.2 ± 0.2 mm and 3.0 ± 0.12 mm–3.5 ± 0.12 mm. Upon rotating the Synergy-S collimator by 90° (i.e., shifting the leaf movement to the gun–target direction), significant reduction of the leaf-end penumbra width (17%) and increase of leaf-side penumbra width (28%) suggest an elliptical shape of the radiation source spot. Similar rotation of the collimator yielded reduction of the penumbras on both leaf-end (34%) and leaf-side (28%) for Novalis, indicating that the Novalis has a more symmetric source size. For all the field sizes and settings, BrainLAB's Novalis μMLC produce a smaller penumbra for simple square fields compared to the Elekta's Synergy-S. However, this difference became less pronounced for leaf-side penumbra and also for circular fields. The tongue-and-groove effect of the Novalis (23 ± 0.9%) is slightly smaller than that of the Synergy-S (25 ± 1%); while the interleaf leakage and leakage directly through leaves for Synergy-S (1.6 ± 0.07% & 0.9 ± 0.04%) are lower than that of Novalis (2 ± 0.08% & 1.3 ± 0.05%).

ERECTA controls low light intensity-induced differential petiole growth independent of Phytochrome B and Cryptochrome 2 action in Arabidopsis thaliana

Plants can respond quickly and profoundly to changes in their environment. Several species, including Arabidopsis thaliana, are capable of differential petiole growth driven upward leaf movement (hyponastic growth) to escape from detrimental environmental conditions. Recently, we demonstrated that the leucine-rich repeat receptor-like Ser/Thr kinase gene ERECTA, explains a major effect Quantitative Trait Locus (QTL) for ethylene-induced hyponastic growth in Arabidopsis. Here, we demonstrate that ERECTA controls the hyponastic growth response to low light intensity treatment in a genetic background dependent manner. Moreover, we show that ERECTA affects low light-induced hyponastic growth independent of Phytochrome B and Cryptochrome 2 signaling, despite that these photoreceptors are positive regulators of low light-induced hyponastic growth.

First report of group 16SrI, ‘Candidatus Phytoplasma asteris’ associated with Mimosa pudica yellows in Indonesia

Mimosa pudica is a perennial plant, widespread in tropical and sub-tropical regions. Known in English as the sensitive plant because of its rapid leaf movements when touched, it is a serious weed in managed grasslands and plantation crops such as coffee, tea and oil palm (Waterhouse, 1993). It is also a popular ornamental plant with medicinal properties. On Samosir Island in North Sumatera, M. pudica is a common invasive species of crops and waste areas. In October 2007, leaf yellowing, little leaf and proliferation of axillary shoots were observed in plants from roadsides and in crop fields around Pangururan village. Leaf and stem samples were collected from three plants with symptoms and one symptomless plant. Total DNA was extracted and used as a template in a nested PCR assay with phytoplasma universal 16S rRNA gene primers R16F2m/R1 and fU5/rU3. All samples with symptoms yielded PCR products of expected size (∼880 bp), and identical HaeIII, RsaI and AluI RFLP profiles. No PCR products were produced with DNA from the symptomless plant. Nested PCR amplicons were purified and directly sequenced (http://www.dnaseq.co.uk). The 16S rDNA sequences were 100% identical, and deposited in GenBank (Accession No. EU273883). BLAST comparisons of the M. pudica phytoplasma 16S rDNA sequence yielded the highest identity (99%) with those of members of group 16SrI, ‘Candidatus Phytoplasma asteris’. Phytoplasmas have been found previously in Indonesia associated with diseases such as legume witches’ broom (Roechan et al., 1978), chilli and tamarillo diseases (Harling et al., 2009) and Kalimantan coconut wilt (Warokka et al., 2006), however, none of these have been from ‘Candidatus Phytoplasma asteris’. This is the first record of a yellows disease on M. pudica worldwide, its association with a phytoplasma and identification of ‘Ca. Phytoplasma asteris’ in Indonesia. Work in the UK was done under Defra plant health licence no. PHL 174B/4612(09/20003).