Sensitivity to Abscisic Acid Modulates Positive Interactions between Arabidopsis thaliana Individuals

The ability of abscisic acid (ABA) to modulate positive interactions between Arabidopsis thaliana individuals under salinity stress was investigated using abi1-1 (insensitive to ABA), era1-2 (hypersensitive to ABA) mutant and wild type plants. The results showed that sensitivity to ABA affects relative interaction intensity (RII) between Arabidopsis thaliana individuals. The neighbor removal experiments also confirmed the role of phenotypic responses in linking plant-plant interactions and sensitivity to ABA. For abi1-1 mutants, the absolute value differences between neighbor removal and control of stem length, root length, leaf area, leaf thickness, flower density, above biomass/belowground biomass (A/U), photosynthetic rate, stomatal conductance, leaf water content and water-use efficiency were smaller than those of the wild type, while for era1-2 mutants, these absolute value differences were larger than those of the wild type. Thus, it is suggested that positive interactions between Arabidopsis thaliana individuals are at least partly modulated by different sensitivity to ABA through different physiological and phenotypic plasticity.     

Sensitivity to Abscisic Acid Modulates Positive Interactions between Arabidopsis thaliana Individuals

The ability of abscisic acid (ABA) to modulate positive interactions between Arabidopsis thaliana individuals under salinity stress was investigated using abi1-1 (insensitive to ABA), era1-2 (hypersen- sitive to ABA) mutant and wild type plants. The results showed that sensitivity to ABA affects relative interaction intensity (RII) between Arabidopsis thaliana individuals. The neighbor removal experiments also confirmed the role of phenotypic responses in linking plant-plant interactions and sensitivity to ...     

Genetic Variation for Life History Sensitivity to Seasonal Warming in Arabidopsis thaliana

Climate change has altered life history events in many plant species; however, little is known about genetic variation underlying seasonal thermal response. In this study, we simulated current and three future warming climates and measured flowering time across a globally diverse set of Arabidopsis thaliana accessions. We found that increased diurnal and seasonal temperature (1°–3°) decreased flowering time in two fall cohorts. The early fall cohort was unique in that both rapid cycling and overwintering life history strategies were revealed; the proportion of rapid cycling plants increased by 3–7% for each 1° temperature increase. We performed genome-wide association studies (GWAS) to identify the underlying genetic basis of thermal sensitivity. GWAS identified five main-effect quantitative trait loci (QTL) controlling flowering time and another five QTL with thermal sensitivity. Candidate genes include known flowering loci; a cochaperone that interacts with heat-shock protein 90; and a flowering hormone, gibberellic acid, a biosynthetic enzyme. The identified genetic architecture allowed accurate prediction of flowering phenotypes (R² > 0.95) that has application for genomic selection of adaptive genotypes for future environments. This work may serve as a reference for breeding and conservation genetic studies under changing environments.     

Ectopic BASL Reveals Tissue Cell Polarity throughout Leaf Development in Arabidopsis thaliana

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Responses to CO2 Enrichment by Two Genotypes of Arabidopsis thaliana Differing in their Sensitivity to Nutrient Availability

The responses of two genotypes of Arabidopsis thaliana, whichdiffer in their sensitivities to nutrients to present and predictedfuture CO₂ concentration were determined under rich vs. poornutrient regimes on the basis of both single traits and thewhole plant. Based on individual traits, the two genotypes respondedsimilarly to CO₂ enrichment for all the traits measured exceptfor rate of increase in crown diameter, for which a decreasewas observed in the less nutrient-sensitive genotype grown atincreased CO₂. Based on the overall response of the whole plant,by analysing groups of plant traits using multivariate analysis,the two genotypes differed substantially from one another andboth responded more strongly to nutrient availability than toCO₂ concentration, especially for traits measured at harvestthat related to reproductive fitness. The less nutrient-sensitivegenotype also showed a weaker overall response to CO₂, and thepattern of the overall response was strikingly similar at differentnutrient supply. In contrast, the more nutrient-sensitive genotyperesponded more strongly to CO₂ than the less nutrient-sensitivegenotype, and responded differently to CO₂ at low vs. high nutrientavailability.Copyright 1995, 1999 Academic Press Plasticity, CO₂ enrichment, nutrient status, nutrient x CO₂ interaction, Arabidopsis thaliana, canonical analysis     

Physiology of Hormone Autonomous Tissue Lines Derived From Radiation-Induced Tumors of Arabidopsis thaliana

γ-Radiation-induced tumors of Arabidopsis thaliana L. have been produced as a novel approach to isolation of genes that regulate plant development. Tumors excised from irradiated plants are hormone autonomous in culture and have been maintained on hormone-free medium for up to 4 years. Five tumor tissue lines having different morphologies and growth rates were analyzed for auxin, cytokinin, and 1-aminocyclopropane-1-carboxylic acid (ACC) content, ethylene production, and response to exogenous growth regulators. Normal tissues and two crown gall tissue lines were analyzed for comparison. Rosettes and whole seedlings each contained approximately 30 nanograms· (gram fresh weight)⁻¹ free indoleacetic acid (IAA), 150 nanograms· (gram fresh weight)⁻¹ ester-conjugated IAA, and 10 to 20 micrograms· (gram fresh weight)⁻¹ amide-conjugated IAA. The crown gall lines contained similar amounts of free and ester-conjugated IAA but less amide conjugates. Whereas three of the radiation-induced tumor lines had IAA profiles similar to normal tissues, one line had 10- to 100-fold more free IAA and three- to 10-fold less amide-conjugated IAA. The fifth line had normal free IAA levels but more conjugated IAA than control tissues. Whole seedlings contained approximately 2 nanograms· (gram fresh weight)⁻¹ of both zeatin riboside and isopentenyladenosine. The crown gall lines had 100- to 1000-fold higher levels of each cytokinin. In contrast, the three radiation-induced tumor lines analyzed contained cytokinin levels similar to the control tissue. The radiation-induced tumor tissues produced very little ethylene, although each contained relatively high levels of ACC. Normal callus contained similar amounts of ACC but produced several times more ethylene than the radiation-induced tumor lines. Each of the radiation-induced tumor tissues displayed a unique set of responses to exogenously supplied growth regulators. Only one tumor line showed the same response as normal callus to both auxin and cytokinin feeding. In some cases, one or more tumor lines showed increased sensitivity to certain growth substances. In other cases, growth regulator feeding had no significant effect on tumor tissue growth. Morphology of the radiation-induced tumor tissues generally did not correlate with auxin to cytokinin ratio in the expected manner. The results suggest that a different primary genetic event led to the formation of each tumor and that growth and differentiation in the tumor tissue lines are uncoupled from the normal hormonal controls.     

Pathways to meiotic recombination in Arabidopsis thaliana

Meiosis is a central feature of sexual reproduction. Studies in plants have made and continue to make an important contribution to fundamental research aimed at the understanding of this complex process. Moreover, homologous recombination during meiosis provides the basis for plant breeders to create new varieties of crops. The increasing global demand for food, combined with the challenges from climate change, will require sustained efforts in crop improvement. An understanding of the factors that control meiotic recombination has the potential to make an important contribution to this challenge by providing the breeder with the means to make fuller use of the genetic variability that is available within crop species. Cytogenetic studies in plants have provided considerable insights into chromosome organization and behaviour during meiosis. More recently, studies, predominantly in Arabidopsis thaliana, are providing important insights into the genes and proteins that are required for crossover formation during plant meiosis. As a result, substantial progress in the understanding of the molecular mechanisms that underpin meiosis in plants has begun to emerge. This article summarizes current progress in the understanding of meiotic recombination and its control in Arabidopsis. We also assess the relationship between meiotic recombination in Arabidopsis and other eukaryotes, highlighting areas of close similarity and apparent differences.     

Transgenerational response to stress in Arabidopsis thaliana

Plants exposed to stress pass the memory of exposure to stress to the progeny. Previously, we showed that the phenomenon of transgenerational memory of stress is of epigenetic nature and depends on the function of Dicer-like (DCL) 2 and DCL3 proteins. Here, we discuss a possible role of DNA methylation and function of small RNAs in establishing and maintaining transgenerational responses to stress. Our new data report that memory of stress is passed to the progeny predominantly through the female rather than male gamete. Possible evolutionary advantages of this mechanism are also discussed.Key words: transgenerational response to stress, Arabidopsis thaliana, maternal inheritance, methylation changes, homologous recombination frequency, genome instability, adaptive response, dcl2, dcl3Plants are sedentary organisms and thus can not respond to rapidly changing growth conditions by escaping to new environments as animals usually do. Moreover, since seed dispersal is rather limited in the vast majority of plants, the progeny is very likely to grow under the same environmental growth conditions as its parents did. The memory of pre-existing growth conditions can be advantageous for plant survival. The environmental experience of parents can be recorded in the form of induced epigenetic modifications that occur in somatic cell lineages. The very late, almost at the end of plant development, separation of germline cells from somatic tissues enables incorporation of acquired epigenetic changes in the gametes. Indeed, previous reports suggested that the progeny of exposed plants might have an advantage while growing in the same environment as its parents.^1–3 Despite a growing number of experimental evidences that support the existence of the phenomenon of memory of stress, the data on adaptive changes in the progeny of stressed plants are scarce.Parental exposure to stress may not only lead to adaptive effects in progeny but also introduce a certain degree of changes in genome stability.^4–9 Our early report showed that the progeny of tobacco plants infected with tobacco mosaic virus had an increased meiotic recombination frequency.⁸ A more recent report demonstrated that these progeny plants had a higher frequency of rearrangements at the loci carrying the homology to N-gene-like R-gene loci, allowing speculations about a possible role of these rearrangements in pathogen resistance evolution.⁹ Similarly, a study of Molinier et al. (2006) showed that the progeny of plants exposed to UVC or flagellin had an increased frequency of somatic homologous recombination events (HRF).⁴ The authors demonstrated that an increase in HRF triggered by a single exposure to UVC was maintained for five consecutive generations in the absence of stress. In contrast, our most recent reports demonstrated that maintaining an increase in HRF caused by ancestral exposure to heat, cold, flood, UVC or salt required exposure to stress in subsequent generations: if F1 plants were propagated for one more generation without stress, the effect diminished and HRF returned back to the level observed in the progeny of untreated plants.^6,7 This scenario seems to be more probable from an evolutionary point of view. Within a given environmental niche, plants establish certain genetic and epigenetic traits needed to cope with the expected growth conditions. Drastic environmental changes or new unusual stresses may trigger a cascade of gene expression changes in attempt to survive and adapt to new conditions. Some of these potentially advantageous changes are most probably recorded in the form of DNA methylation and chromatin modifications and are passed to progeny as memory of stress exposure.It can be further hypothesized that if these new environmental conditions are no longer present during the lifespan of future generations, the newly established methylation patterns and chromatin organization will return to the original epigenetic landscape that was the most adequate fit for this environmental niche. If the same new stresses occur in consecutive generations, the newly established epigenetic changes will be maintained and possibly stabilized after many generations of exposure.     

Tolerance of Arabidopsis thaliana to the Allelochemical Protocatechualdehyde

We investigated the effects of the secondary metabolite protocatechualdehyde (PCA, 3,4-dihydroxybenzaldehyde) on stress markers, including fluorescence parameters and the concentrations of pigments, free radicals, protein, and lipid peroxides, in adult plants of Arabidopsis thaliana. The content of proline, carotenoids, and chlorophylls a and b peaked 9?h after administration of 3?mM PCA (the highest concentration used in this study), although malonyldialdehyde and dry mass contents peaked 24?h following PCA treatment. Leaf staining revealed peak production of O₂ ^? between 30 and 90?min post-treatment and peak production of H₂O₂ between 1 and 9?h post-treatment. Several effects, including the observed furling of leaf margins (leaf rolling), the increases in proline content and dry to fresh weight ratio, and the oxidative burst, are reminiscent of the plant response to drought. Early dehydration in PCA-treated plants was confirmed by decreases in leaf water potential, relative water content, and stomatal opening in the first hours of treatment. Thus, PCA seems to be either inducing water deficiency stress (probably through action in the roots) or directly triggering antidrought defenses. In either case, plants showed tolerance to the concentrations employed in this study, with most of the parameters observed having recovered control values within a week of treatment.     

Direct gene transfer to protoplasts of Arabidopsis thaliana

We performed a series of direct gene transfer experiments with protoplasts of Arabidopsis thaliana ecotype Zürich. An average of more than 100 transformants were selected per 10⁶6 treated protoplasts. Stable transformation was confirmed by integration of the marker gene into high molecular weight DNA and by its genetic transmission to subsequent offspring generations.Abbreviations ATF absolute transformation frequency - PEG polyethyleneglycol - hpt hygromycin phosphotransferase gene - CTAB N-Cetyl-N,N,N-trimethyl-ammonium bromide - MES 2-(N-morpholino)ethanesulfonic acid     

Sugar and Light Effects on the Condition of the Photosynthetic Apparatus of Arabidopsis thaliana Cultured in vitro

Light and sugars are fundamental elements of plant metabolism and play signaling roles in many processes. They are also critical factors determining the condition of plants cultured in vitro. The aim of this work was to investigate the simultaneous influence of irradiance and sugar content in the medium on the growth and photosynthetic apparatus condition of Arabidopsis thaliana in vitro. Plants were grown on media containing 1 or 3% of sucrose or glucose at three irradiances: 25, 100, and 250 μmol m⁻² s⁻¹ (weak, medium, and strong light). Media without sugar were used for control plants. Plant growth parameters were measured and the following physiological processes were investigated: photosynthesis, blue light-induced chloroplast relocations, and xanthophyll cycle activity. The expression of genes related to these processes was analyzed. The presence of sugar in the medium was found to be essential for the growth of Arabidopsis in vitro. Weak light significantly limited growth and the capacity to acclimate to changing light conditions. Strong light was a source of stress in some cases. Contrary to earlier reports, exogenous sugars showed a positive effect on photosynthesis. At higher concentration they acted as photoprotectants, overcoming the negative influence of strong light on photosynthesis and the xanthophyll cycle. The expression of all investigated genes was influenced by irradiance and sugar presence. In many cases differential effects of sugar type and concentration could be observed. The specific effects of some irradiance/sugar concentration combinations point to possible interactions between sugar- and light-induced signaling pathways.     

The Ca2+ Pump of the Plasma Membrane of Arabidopsis thaliana: Characteristics and Sensitivity to Fluorescein Derivatives

The transport and hydrolytic activities of the plasma membrane (PM) Ca²⁺ pump were characterized in a PM fraction purified from seedlings of Arabidopsis thaliana by the aqueous two-phase partitioning technique. Ca²⁺ uptake could be energized by ATP and by ITP (at about 70% the rate sustained by ATP). This characteristic was used to measure the hydrolytic activity of the enzyme as Ca²⁺-dependent ITPase activity. The PM Ca²⁺ pump displayed a broad pH optimum around pH 7.2, was drastically inhibited by erythrosin B (EB), and was half-saturated by 60 μM ITP. It was stimulated by CaM, specially at low, non-saturating Ca²⁺ concentrations. All of these characteristics closely resemble those of the PM Ca²⁺ pump in other plant materials. Analysis of the effects of EB and other fluorescein derivatives (eosin Y and rose bengal) showed that: i) EB behaved as a competitive inhibitor with respect to ITP; ii) the PM Ca²⁺ pump was drastically inhibited by concentrations of fluorescein derivatives (submicromolar), much lower than those required to inhibit the PM H⁺-ATPase; iii) the different fluorescein derivatives were diversely efficient in inhibiting the activities of the Ca²⁺ pump and of the H⁺-ATPase of the PM (eosin Y was about 10000-fold, EB 1000-fold and rose bengal only 50-fold more active on the Ca²⁺ pump than on the H⁺-ATPase); and iv) the effectiveness of EB in inhibiting the Ca²⁺ pump was strongly affected by the protein concentration in the assay medium.     

Arabidopsis thaliana proteomics: from proteome to genome

Proteomics has become an important approach for investigating cellular processes and network functions. Significant improvements have been made during the last few years in technologies for high-throughput proteomics, both at the level of data analysis software and mass spectrometry hardware. As proteomics technologies advance and become more widely accessible, efforts of cataloguing and quantifying full proteomes are underway to complement other genomics approaches, such as RNA and metabolite profiling. Of particular interest is the application of proteome data to improve genome annotation and to include information on post-translational protein modifications with the annotation of the corresponding gene. This type of analysis requires a paradigm shift because amino acid sequences must be assigned to peptides without relying on existing protein databases. In this review, advances and current limitations of full proteome analysis are briefly highlighted using the model plant Arabidopsis thaliana as an example. Strategies to identify peptides are also discussed on the basis of MS/MS data in a protein database-independent approach.     

Cardiolipin synthase of Arabidopsis thaliana

Functional expression studies in microorganisms showed that the Arabidopsis thaliana gene At4g04870 represents the cardiolipin synthase (CLS) gene encoding a hydrophobic preprotein of 38 kDa with a cleavable signal peptide for the import into mitochondria. CLS of Arabidopsis over-expressed in Escherichia coli has an alkaline pH optimum, a strict requirement for divalent cations and a distinctly lower K(m) for cytidinediphosphate-diacylglycerol than for phosphatidylglycerol. It displayed a preference for both its substrates esterified with unsaturated acyl groups. Solubilization and purification experiments revealed that the protein requires a defined phospholipid environment, particularly the presence of cardiolipin, to acquire its catalytically active conformation.     

Cadmium-Sensitive Mutants of Arabidopsis thaliana

A screening procedure for identifying Cd-sensitive mutants of Arabidopsis thaliana is described. With this procedure, two Cd-sensitive mutants were isolated. These represent independent mutations in the same locus, referred to as CAD1. Genetic analysis has shown that the sensitive phenotype is recessive to the wild type and segregates as a single Mendelian locus. Crosses of the mutant to marker strains showed that the mutation is closely linked to the tt3 locus on chromosome 5. In addition to Cd, the mutants are also significantly more sensitive to mercuric ions and only slightly more sensitive to Cu and Zn, while being no more sensitive than the wild type to Mn, thus indicating a degree of specificity in the mechanism affected by the mutation. Undifferentiated callus tissue is also Cd sensitive, suggesting that the mutant phenotype is expressed at the cellular level. Both wild-type and mutant plants showed increased sensitivity to Cd in the presence of buthionine sulfoximine, an inhibitor of the biosynthesis of the cadmium-binding (γ-glutamylcysteine)_n-glycine peptides, suggesting that the mutant is still able to synthesize these peptides. However, the effects of a cad1 mutation and buthionine sulfoximine together on cadmium sensitivity are essentially nonadditive, indicating that they may affect different aspects of the same detoxification mechanism. Assays of Cd uptake by intact plants indicate that the mutant is deficient in its ability to sequester Cd.     

Mesophyll conductance to CO2 in Arabidopsis thaliana

The close rosette growth form, short petioles and small leaves of Arabidopsis thaliana make measurements with commercial gas exchange cuvettes difficult. This difficulty can be overcome by growing A. thaliana plants in 'ice-cream cone-like' soil pots. This design permitted simultaneous gas exchange and chlorophyll fluorescence measurements from which the first estimates of mesophyll conductance to CO(2) (g(m)) in Arabidopsis were obtained and used to determine photosynthetic limitations during plant ageing from c. 30-45 d. Estimations of g(m) showed maximum values of 0.2 mol CO(2) m(-2) s(-1) bar(-1), lower than expected for a thin-leaved annual species. The parameterization of the response of net photosynthesis (A(N)) to chloroplast CO(2) concentrations (C(c)) yielded estimations of the maximum velocity of carboxylation (V(c,max_Cc)) which were also lower than those reported for other annual species. As A. thaliana plants aged from 30 to 45 d, there was a 40% decline of A(N) that was entirely the result of increased diffusional limitations to CO(2) transfer, with g(m) being the largest. The results suggest that in A. thaliana A(N) is limited by low g(m) and low capacity for carboxylation. Decreased g(m) is the main factor involved in early age-induced photosynthetic decline.