Phosphate starvation alters calcium signalling in roots of Arabidopsis thaliana

Low bioavailability of phosphate (P) due to low concentration and high immobility in soils is a key limiting factor in crop production. Application of excess amounts of P fertilizer is costly and by no means sustainable, as world-wide P resources are finite and running out. To facilitate the breeding of crops adapted to low-input soils, it is essential to understand the consequences of P deficiency. The second messenger calcium (Ca2+) is known to signal in plant development and stress perception, and most recently its direct role in signalling nutrient availability and deficiency has been partially elucidated. The use of Ca2+ as a signal has to be tightly controlled, as Ca2+ easily complexes with P groups and therefore is highly toxic to cellular P metabolism. It is unknown whether Ca2+ signals P availability or whether signalling is altered under P starvation conditions. The aim of this PhD project was to characterise the use of Ca2+ ions, particularly cytosolic free Ca2+ ([Ca2+]cyt), in stress signalling by P-starved roots of the model plant Arabidopsis thaliana. The hypothesis was that under P starvation and a resulting decreased cellular P pool, the use of [Ca2+]cyt may have to be restricted to avoid cytotoxic complexation of Ca2+ with limited P groups. Employing a range of genetically encoded Ca2+ reporters in Arabidopsis, P starvation but not nitrogen starvation was found to strongly dampen the root [Ca2+]cyt increases evoked by mechanical, salt, osmotic, and oxidative stress as well as by extracellular nucleotides. The strongly altered root [Ca2+]cyt response to extracellular nucleotides was shown to manifest itself during seedling development under chronic P deprivation, but could be reversed by P resupply. Fluorescent imaging elucidated that P-starved roots showed a normal [Ca2+]cyt response to extracellular nucleotides at the apex, but a strongly dampened [Ca2+]cyt response in distal parts of the root tip, correlating with high reactive oxygen species (ROS) levels induced by P starvation. Excluding iron, as well as P, rescued the altered [Ca2+]cyt response, and restored ROS levels to those seen under nutrient-replete conditions. P availability was not signalled through [Ca2+]cyt. In another part of this PhD project, a library of 77 putative Ca2+ channel mutants was compiled and screened for aberrant root hair growth under P starvation conditions. No mutant line showed aberrant root hair growth. These results indicate that P starvation strongly affects stress-induced [Ca2+]cyt modulations. The data generated in this thesis further understanding of how plants can integrate nutritional and environmental cues, adding another layer of complexity to the use of Ca2+ as a signal transducer.BBSRC DT

Iron availability modulates the Arabidopsis thaliana root calcium signature evoked by exogenous ATP.

Plants use changes in cytosolic free Ca2+ ("signatures") to encode information from the specific signals generated in development, immunity and stress perception. Phosphate availability has a significant impact on the Arabidopsis thaliana root calcium signatures generated in response to abiotic stress stimuli and exogenous purine nucleotides. In the case of the response to exogenous ATP, the effect of low phosphate availability is linked to abnormal iron and reactive oxygen species accumulation with iron deprivation's restoring normal signature dynamics. Here, the effect of iron deprivation with normal phosphate availability has been examined. Iron deprivation significantly alters the root calcium signature evoked by exogenous ATP and may link to levels of reactive oxygen species and callose deposition

Sozialistischer Realismus – Widerspiegelungstheorie.: Ein Gespräch

Hartmut Krones: Guten Tag und einen guten Nachmittag. Ich habe hier die Ehre, das folgende Gespräch und die mögliche Diskussion zu leiten. Ansonsten aber werde ich mich eher im Hintergrund halten. Wir haben jetzt, nachdem wir über die Institutionen gesprochen haben am Vormittag und auch über persönliche Schicksale und persönliche Befindlichkeiten, einen Gegenstand der Musikästhetik vor uns, und zwar insbesondere jene musikästhetische Position, die die offizielle Position der sozialistischen Länder und nicht nur der DDR war. Sie sehen es am Thema – Sozialistischer Realismus und Widerspiegelungstheorie. Das heißt, wir gehen jetzt in die musikalische Praxis, die, wie Sie gleich hören werden, sehr wohl politisch indoktriniert wurde. Ich glaube, ich brauche die beiden Redner hier nicht weiter vorzustellen: Klaus Mehner, Professor für Systematische Musikwissenschaft an der Universität Leipzig, zeitweise auch Direktor des Instituts und durch zahlreiche Publikationen hervorgetreten, und Siegfried Matthus, erfolgreicher Komponist, auch im Westen, und jeder wird auf seine Art zu diesem Thema etwas sagen, und dann werden wir sehen, wie groß und wie weit die Diskussion eröffnet werden muss

Calcium-Mediated Abiotic Stress Signaling in Roots.

Roots are subjected to a range of abiotic stresses as they forage for water and nutrients. Cytosolic free calcium is a common second messenger in the signaling of abiotic stress. In addition, roots take up calcium both as a nutrient and to stimulate exocytosis in growth. For calcium to fulfill its multiple roles must require strict spatio-temporal regulation of its uptake and efflux across the plasma membrane, its buffering in the cytosol and its sequestration or release from internal stores. This prompts the question of how specificity of signaling output can be achieved against the background of calcium's other uses. Threats to agriculture such as salinity, water availability and hypoxia are signaled through calcium. Nutrient deficiency is also emerging as a stress that is signaled through cytosolic free calcium, with progress in potassium, nitrate and boron deficiency signaling now being made. Heavy metals have the capacity to trigger or modulate root calcium signaling depending on their dose and their capacity to catalyze production of hydroxyl radicals. Mechanical stress and cold stress can both trigger an increase in root cytosolic free calcium, with the possibility of membrane deformation playing a part in initiating the calcium signal. This review addresses progress in identifying the calcium transporting proteins (particularly channels such as annexins and cyclic nucleotide-gated channels) that effect stress-induced calcium increases in roots and explores links to reactive oxygen species, lipid signaling, and the unfolded protein response.Funding for this work was from the BBSRC (BB/K009869/1 and Doctoral Training Programme) and the University of Cambridge Broodbank Trust.This is the final version of the article. It first appeared from Frontiers at http://dx.doi.org/10.3389/fpls.2016.01296

Phosphate Deprivation Can Impair Mechano-Stimulated Cytosolic Free Calcium Elevation in Arabidopsis Roots.

The root tip responds to mechanical stimulation with a transient increase in cytosolic free calcium as a possible second messenger. Although the root tip will grow through a heterogeneous soil nutrient supply, little is known of the consequence of nutrient deprivation for such signalling. Here, the effect of inorganic phosphate deprivation on the root's mechano-stimulated cytosolic free calcium increase is investigated. Arabidopsisthaliana (cytosolically expressing aequorin as a bioluminescent free calcium reporter) is grown in zero or full phosphate conditions, then roots or root tips are mechanically stimulated. Plants also are grown vertically on a solid medium so their root skewing angle (deviation from vertical) can be determined as an output of mechanical stimulation. Phosphate starvation results in significantly impaired cytosolic free calcium elevation in both root tips and whole excised roots. Phosphate-starved roots sustain a significantly lower root skewing angle than phosphate-replete roots. These results suggest that phosphate starvation causes a dampening of the root mechano-signalling system that could have consequences for growth in hardened, compacted soils

The tricot approach. Guide for large-scale participatory experiments

Triadic comparison of technology options (tricot) is a research methodology that helps farmers to identify the most suitable technologies for the local conditions of their farm. Tricot (read: ‘try-cot’) engages farmers as ‘farmer researchers’ in the testing or validation of new crop varieties and other promising technologies. Tricot is supported by the ClimMob digital platform (https://climmob.net). This guide provides an introduction to tricot and each of the steps in the experimental cycle

DORN1/P2K1 and purino-calcium signalling in plants: making waves with extracellular ATP.

BACKGROUND AND AIMS:Extracellular ATP governs a range of plant functions, including cell viability, adaptation and cross-kingdom interactions. Key functions of extracellular ATP in leaves and roots may involve an increase in cytosolic free calcium as a second messenger ('calcium signature'). The main aim here was to determine to what extent leaf and root calcium responses require the DORN1/P2K1 extracellular ATP receptor in Arabidopsis thaliana. The second aim was to test whether extracellular ATP can generate a calcium wave in the root. METHODS:Leaf and root responses to extracellular ATP were reviewed for their possible links to calcium signalling and DORN1/P2K1. Leaves and roots of wild type and dorn1 plants were tested for cytosolic calcium increase in response to ATP, using aequorin. The spatial abundance of DORN1/P2K1 in the root was estimated using green fluorescent protein. Wild type roots expressing GCaMP3 were used to determine the spatial variation of cytosolic calcium increase in response to extracellular ATP. KEY RESULTS:Leaf and root ATP-induced calcium signatures differed markedly. The leaf signature was only partially dependent on DORN1/P2K1, while the root signature was fully dependent. The distribution of DORN1/P2K1 in the root supports a key role in the generation of the apical calcium signature. Root apical and sub-apical calcium signatures may operate independently of each other but an apical calcium increase can drive a sub-apical increase, consistent with a calcium wave. CONCLUSION:DORN1 could underpin several calcium-related responses but it may not be the only receptor for extracellular ATP in Arabidopsis. The root has the capacity for a calcium wave, triggered by extracellular ATP at the apex

Arabidopsis thaliana CYCLIC NUCLEOTIDE-GATED CHANNEL2 mediates extracellular ATP signal transduction in root epidermis.

Funder: Agence Nationale de la Recherche; Id: http://dx.doi.org/10.13039/501100001665Funder: Canadian Network for Research and Innovation in Machining Technology, Natural Sciences and Engineering Research Council of Canada; Id: http://dx.doi.org/10.13039/501100002790Damage can be signalled by extracellular ATP (eATP) using plasma membrane (PM) receptors to effect cytosolic free calcium ion ([Ca2+ ]cyt ) increase as a second messenger. The downstream PM Ca2+ channels remain enigmatic. Here, the Arabidopsis thaliana Ca2+ channel subunit CYCLIC NUCLEOTIDE-GATED CHANNEL2 (CNGC2) was identified as a critical component linking eATP receptors to downstream [Ca2+ ]cyt signalling in roots. Extracellular ATP-induced changes in single epidermal cell PM voltage and conductance were measured electrophysiologically, changes in root [Ca2+ ]cyt were measured with aequorin, and root transcriptional changes were determined by quantitative real-time PCR. Two cngc2 loss-of-function mutants were used: cngc2-3 and defence not death1 (which expresses cytosolic aequorin). Extracellular ATP-induced transient depolarization of Arabidopsis root elongation zone epidermal PM voltage was Ca2+ dependent, requiring CNGC2 but not CNGC4 (its channel co-subunit in immunity signalling). Activation of PM Ca2+ influx currents also required CNGC2. The eATP-induced [Ca2+ ]cyt increase and transcriptional response in cngc2 roots were significantly impaired. CYCLIC NUCLEOTIDE-GATED CHANNEL2 is required for eATP-induced epidermal Ca2+ influx, causing depolarization leading to [Ca2+ ]cyt increase and damage-related transcriptional response