1,721,223 research outputs found
UV-B radiation affects plant volatile emissions and shade avoidance responses
No full textPlants detect and integrate an assortment of signals from their environment, and use these signals to maximise their performance by adjusting their growth and development as well as their secondary metabolite production. In this thesis, we investigated how plants integrate visual and olfactory signals. First, a system to measure plant volatile organic compounds (VOCs) was set up (chapter 2). Second, the effect of UV-B radiation on tomato and Arabidopsis thaliana VOC emissions was described and its regulation via TERPENE SYNTHASE gene expression and the UV-B photoreceptor UVR8 examined (chapter 3 and 4). Third, the interaction between UV-B and low red to far-red (R:FR) responses was investigated at the physiological and signal transduction level (chapter 5). In tomato, UV-B induced VOC emissions with differential timing: a first class of VOCs increased immediately upon UV-B exposure, a second class of compounds had a delayed response and a third class increased only after UV-B exposure stopped. This third class included monoterpenes and methyl salicylate (MeSA), compounds known to function as signals in ecological interactions. We identified six different monoterpenes that were induced by UV-B, but found no correlation between their induced emission and up-regulation of their TERPENE SYNTHASE (TPS) genes, except for β-phellandrene and TPS4 expression in leaves. Using Arabidopsis thaliana, we demonstrated that UV-B induces VOC emissions independent of the UV-B photoreceptor UVR8. These are the first data showing that some secondary metabolites are regulated by UV-B exposure in a UVR8-independent manner. In addition, comparing UV-B-mediated VOC emissions of tomato and A. thaliana revealed that (i) the timing of UV-B-induced monoterpene emissions and (ii) UV-B-induced MeSA emissions are species specific. By exposing A. thaliana to UV-B and low R:FR simultaneously, we demonstrated that UV-B represses low R:FR responses via the UVR8 pathway and that this interaction involves several components of the R:FR signalling network. Mutant studies indicated involvement in the UV-FR interaction of the early UVR8-signalling component HY5, growth-repressing DELLA proteins, central shade avoidance regulators PIF4 and PIF5, but possibly also PIF1 and PIF3, auxin-related and PIF-inhibiting PAR1, and photoreceptor-interacting PKS2. In addition, gene expression studies suggested a role for the PAR1-binding and BR-inducible transcription factor PRE1, as well as for HFR1, which inhibits PIF4 and PIF5 action. Concerning the involvement of hormones in the UV-FR interaction, we found that BR might be important, whereas we found no such evidence for auxin and GA. This thesis thus demonstrates that plant responses to distinct environmental cues interact, and that there is cross-talk between the intrinsic signalling pathways a plant uses to assess and respond to light quality changes. This is especially relevant when considering plant responses in patchy environments
Above-ground plant interactions: consequences for growth and volatile emission
No full textThe environment that plants grow in can be highly dynamic through a plant’s lifetime. In many cases, plants have to compete with other plants in their direct surroundings for a limited pool of resources. Competitive interactions among plants shape vegetation composition and control biodiversity, making it one of the most important processes for the development of local vegetation patterns. To compete successfully, plants exploit a range of phenotypic responses that enhance resource capture and thus increase their fitness during competition. These responses depend on detection of proximate neighbours and adequate responses to the environment. This thesis describes the earliest cues that are involved in the detection of neighbouring plants. Further, the effect of competition for light on the emission and functionality of volatile organic compounds (VOCs) is investigated. In chapter 2, the touch of leaftips of neighbouring plants is introduced as a cue to detect these neighbours. In Arabidopsis thaliana, this touch functions as the earliest signal to detect neighbours. Duet o this touch, leafs are more vertically orientated (which is called hyponasty). This leads to an environment in which the red to farred ratio decrease, which is the next cue for plants to detect neighbours. In chapter 3, the interaction between the volatile plant hormone ethylene and a reduction in R:FR was further investigated. Here, it is described that perception of ethylene is required for low R:FR induced petiole elongation, when the R:FR ratio is mildly reduced. At a more severely reduced R:FR ratio, perception of ethylene enhances the rate of hyponastic leaf movement. Chapter 4 describes effects of neighbour-induced alterations in the light environment on VOC emissions in Arabidopsis. Light signals that represent different degrees of competition for light led to similar reductions in the emission of VOCs. The emission of methyl-jasmonate-induced VOCs, was found to be reduced in low R:FR conditions and this affected plant preference of the specialist herbivore Pieris brassicae. In the last experimental chapter, the effect of low R:FR conditions on volatile effects between plants is demonstrated in barley (Hordeum vulgare). When volatile-emitting plants were exposed to low R:FR, VOC emissions were reduced. As a consequence, effects on carbon allocation by VOCs from emitter plants of one cultivar (Alva) on receivers plant from another (Kara) depend highly on the R:FR conditions of the emitter. These data indicate the importance of the light environment on chemical interactions between plants
Genomics of flooding stress tolerance: exploiting natural variation in Arabidopsis thaliana
No full textWater is indispensable for plants. However, both extremes of it, in terms of availability, whether limited (i.e., drought) or excessive (i.e., flooding) are lethal for a plant. The incidence of flooding events, in particular, have increased in the past five decades due to the effect of anthropogenically induced climate change on the global precipitation cycle . Due to the flooding sensitivity of most crop species, this environmental stress causes major losses of crop yield and negatively impacts food production. Hence, the development of tolerant but high yielding varieties is essential. Past research on plant responses to flooding have provided considerable insight into the adaptive responses of relatively flood-tolerant plant species such as rice and Rumex. However, much still needs to be learnt about the (i) the relationship between gene regulation and plant survival and (ii) the genes and mechanisms that determine variation in tolerance to submergence. In the current study, we used the plant model species, Arabidopsis thaliana (Arabidopsis) with a well-characterized genome to identify the genetic components governing the adaptive response to submergence stress. Subsequent translation of thisobtained genomic knowledge from Arabidopsis to crops can aid marker-assistant breeding programs to develop high yielding crop varieties with improved survival under submerged conditions. To achieve our objective, we first exploited the natural variation among a set of 86 Arabidopsis accessions (Chapter 2). Our results demonstrated a considerable natural variation among Arabidopsis accessions for submergence tolerance and allowed the selection of a set of three most tolerant and three most sensitive genotypes. Next, we made a molecular comparison of the response of these six accessions to complete submergence to identify the genetic components that may underlie the observed variation in tolerance. We also characterized the organ-specific submergence-induced molecular adjustments by comparing the hypoxic shoot transcriptome
Shade avoidance : how auxin controls photoreceptor-mediated shoot elongation
No full textPlants perceive the threat of competing neighbours through various signals. They carry sophisticated photoreceptor systems to signal this and subsequently activate an interacting network of various hormones and transcriptional regulators. The complete signal detection and signal transduction network together defines the SAS to be expressed. The aim of the studies in this PhD thesis is to elucidate the hormonal regulation of auxin in the elongation response as part of the SAS. Understanding this mechanism is of interest, not only from a fundamental point of view, but also from an applied point of view. Understanding the hormonal regulation of the SAS could be a target to improve harvest yield of commercial crops. In chapter 2 the blue light-mediated shade avoidance of Arabidopsis seedlings is described. This elongation response is only partly under the control of auxin and requires combined auxin and brassinosteroid action. In this Chapter we investigated cell wall modifying proteins, which are known to regulate cell elongation, as possible regulator of shade avoidance by both auxin and brassiniosteroids. We show that different XTHs were regulated during blue light-mediated shade avoidance and that the requirement of both auxin and brassinosteroid action could be explained by the different XTHs they regulated in the elongation response. Blue light is not the only light signal that can induce shade avoidance in Arabidopsis seedlings. Also reduction of the R:FR induced hypocotyls to elongate, as we show in chapter 3. The data show that, unlike blue light-mediated shade avoidance, auxin action explains the full response. We demonstrate that PIN3, a regulator of polar auxin transport, changes its cellular location in the hypocotyl towards the lateral side of the endodermal hypocotyl cells upon the FR treatment. As a consequence the direction of auxin transport is changed and results in auxin accumulation throughout over the hypocotyl thus inducing elongation. In Chapter 4 the role of auxin (transport) in shade avoidance of full grown plants is studied, not only as a result of changes in light quality but also in dense stand experiments. To examine this, the pin3-3 mutant which lacks the elongation response upon the FR treatment in seedlings, was used. Petioles of pin3-3 are shown to have no response upon FR-treatment but also a delayed response to neigbouring plants. This enabled us to further investigate the role of auxin transport in the response to neighbouring plants but also the functional significance of the SAS for rosette species such as Arabidopsis. Chapter 5 shows how the cellular localization of PIN3 is dependent on intact microtubule (orientation). Disrupting the microtubules inhibits the expression levels of the cell wall modifying protein family of XTHs which are needed for the shade avoidance response of Arabidopsis petioles, through the inhibition of polar auxin transport
When growing tall is not an option: contrasting shade avoidance responses in two wild Geranium species
No full textPlants can deal with shade in different ways. Sun-adapted species express a set of growth traits to reach for light; the so-called shade avoidance syndrome (SAS). However, shade-tolerant species from the forest understory are not able to outgrow surrounding trees and adopt a tolerance strategy including suppression of shade avoidance. All plants sense the drop in the ratio between red (R) and far-red (FR) light via specialized photoreceptors, the phytochromes, but unlike the molecular pathways promoting SAS, virtually nothing is known about the regulation of shade tolerance. We selected two wild Geranium species with opposite growth responses to FR light enrichment; the shade avoiding G. pyrenaicum and shade tolerant G. robertianum. RNA sequencing of these species revealed contrasting transcriptomic changes treated upon FR light and in the first place showed how differential regulation of phytohormone synthesis and –perception could correlate to the species growth patterns in shade. Analysis of the hormone levels and growth responses to auxin, gibberellic acid and brassinosteroid application or –inhibition confirmed a role for these hormones in the Geranium shade responses. Secondly, the transcriptome analysis revealed a striking difference in FR induced regulation of pathogen defences. G. pyrenaicum showed far-red-mediated down-regulation of defence genes and increased susceptibility to the fungal pathogen Botrytis cinerea, similar to model species Arabidopsis. Interestingly, G. robertianum seems to boost its defences and becomes more resistant when exposed to FR-enriched light. Furthermore, the RNAseq analysis identified genes of which the expression patterns match growth data and give an insight into novel possible players and pathways responsible for the opposite light responses; two receptor-like kinases and a bHLH transcription factor. The importance of these novel candidates was verified in heterologous functional studies in Arabidopsis
Hypoxia and development: Air conditional
Full text linkHypoxia has long been studied in relation to anaerobic metabolism. It has now been shown to control development, acting as a cue to maintain the seedling’s protective apical hook and a trigger of developmental decisions both before and after the plantlet emerges from the soil into the light
Molecular regulation of ethylene-induced hyponasty
No full textMany plant species can actively reorient their organs in response to dynamic environmental conditions. Organ movement can be an integral part of plant development or can occur in response to unfavourable external circumstances. Petiole hyponasty is an upward movement driven by a higher rate of cell expansion on the lower (abaxial) compared to the upper (adaxial) side. Hyponasty is common among rosette species facing environmental stresses such as flooding, proximity of neighbours or elevated ambient temperature. The complex regulatory mechanism of hyponasty involves activation of pathways at molecular and developmental levels with ethylene playing a crucial role. Despite the broad knowledge on the functionality and hormonal regulation of ethylene-induced hyponasty and growing insights into the developmental alterations leading to upward petiole movement, there are still many important questions to be answered. The focus of this thesis is the cellular basis and molecular regulation of ethylene-induced hyponastic growth in Arabidiopsis thaliana. A detailed analysis of the epidermal cell sizes and study of cortical microtubule (CMT) reorientation events revealed that, upon ethylene treatment, longitudinal cell expansion occurs in a localized zone of the abaxial side of the petiole. Based on the cell length data a mathematical model is provided that predicts petiole angle change which is highly similar to the observed value. The thesis also describes the use of next generation Illumina sequencing technique as a way of mapping T-DNA insertions in activation-tagging lines. Identification of T-DNA loci in such lines is occasionally problematic due to the complexity of integration events. In a screen of T-DNA activation-tagging lines carrying 35S CaMV enhancers, four candidates were selected. These lines exhibited aberrant petiole angles in control conditions, ethylene and low light treatments. The genomic DNA of those lines was pooled and subjected to Illumina sequencing which resulted in identification of three out of four insertion loci. One of the selected candidates, which exhibited decreased petiole angle in all treatments and was designated ddd1. The phenotype of ddd1 is linked to the T-DNA insertion in the intragenic region of ROTUNDIFOLIA3 (ROT3) gene which encodes an enzyme involved in the synthesis of brassinosteroids (BRs). The lack of cell expansion in ddd1 upon ethylene exposure led to the hypothesis about an interrelation of ethylene and BRs during cell elongation. This is supported by the pharmacological experiments which indicate a potential role of ethylene in sensitisation the tissue to BRs. Furthermore, the thesis aims to describe the involvement of ethylene response factors (ERFs) in regulation of hyponasty. Transcriptional regulation of ERFs during ethylene treatment is shown and possible scenarios of their involvement during the induction of hyponasty are discussed. Over-expression of a core cell cycle gene, CYCA2;1, leads to enhanced hyponasty independent of endoreduplication. It is shown that ethylene inhibits the progression of a mitotic cell cycle and mathematical modelling shows that this fine-tuning process provides a subtle balance between cell expansion and cell division which controls the degree of an upward petiole movement
Genomics of Stress Escape in Arabidopsis Thaliana
No full textIn nature, two highly diverse environmental signals, flooding and shade, sensed through their own unique receptor systems, share physiological and molecular similarities in the context of accelerated shoot elongation in plants (a conserved stress-escape strategy), suggesting a possible cross-talk between the two signals. This shoot elongation response is mediated by ethylene accumulating in flooding and by changes in light quality and quantity under vegetation shade. Our aim was to find out the common physiological regulators of this elongation phenotype, as it becomes easy to limit this fast growth and thereby conserve energy and increase plant yield in different stresses (similar to semi-dwarf crop varieties of green revolution with mutated GA20OX1). We adopted hypocotyl elongation as a proxy for shoot elongation and delineated Arabidopsis hypocotyl length kinetics in response to ethylene and shade. Based on the kinetics, we further investigated ethylene and shade-induced genome-wide temporal gene expression changes in hypocotyls and cotyledons separately. Hypocotyl transcriptome was reconfigured more than the cotyledon transcriptome. Bioinformatics analyses hinted towards contrasting regulation of growth promotion- and photosynthesis-related genes. Correlational analysis of organ-specific transcriptomic changes to hormone microarray data suggested a strong induction of auxin, brassinosteroid and gibberellin signatures in the elongating hypocotyls. Finally, we characterized and discussed the possible connections between the candidate genes to give an overview of the signal integration between ethylene and shade during hypocotyl growth in response to the two signals. We found evidence of both negative and positive players being transcriptionally induced by same stresses to modulate growth and by using the same set of hormone genes. In nature, plants often encounter various environmental stresses simultaneously. As such using a conserved set of molecular players to resist many stresses is advantageous to the plants
Effects of experimental snowmelt and rain on dispersal of six plant species
No full textWater flows affect dispersal of propagules of many plant species, and rivers and streams are therefore very important dispersal vectors. However, small water flows such as trough rain and snowmelt are much more common, but their effects on dispersal are barely studied. The importance of this form of dispersal deserves attention, especially when considering that climate change is predicted to change the amounts of rain and snow worldwide. Dispersal through melting snow and rain was addressed experimentally, using artificial soils mounted on slopes with different angles and subjected to a melting snow pack or an equivalent amount of dripping water. Seeds on the soil moved on average 3.02 cm (+/- 1.81 SE) in rain treatments and 0.23 cm (+/- 0.3 SE) in snowmelt treatments. Tracking plastic granules in field conditions further showed that snowmelt exhibited minimal dispersal capacity. Dispersal distances by rain were enhanced by increasing slope angles and with decreasing seed volume. Given that many species in cold environments have small seeds, dispersal by rain could provide an important (secondary) dispersal mechanism in these habitats
Shade avoidance: phytochrome signalling and other aboveground neighbour detection cues
No full textPlants compete with neighbouring vegetation for limited resources. In competition for light, plants adjust their architecture to bring the leaves higher in the vegetation where more light is available than in the lower strata. These architectural responses include accelerated elongation of the hypocotyl, internodes and petioles, upward leaf movement (hyponasty), and reduced shoot branching and are collectively referred to as the shade avoidance syndrome. This review discusses various cues that plants use to detect the presence and proximity of neighbouring competitors and respond to with the shade avoidance syndrome. These cues include light quality and quantity signals, mechanical stimulation, and plant-emitted volatile chemicals. We will outline current knowledge about each of these signals individually and discuss their possible interactions. In conclusion, we will make a case for a whole-plant, ecophysiology approach to identify the relative importance of the various neighbour detection cues and their possible interactions in determining plant performance during competition
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