Overexpression of Arabidopsis thaliana tryptophan synthase beta 1 (AtTSB1) in Arabidopsis and tomato confers tolerance to cadmium stress

Tryptophan regulates sorghum root growth and enhances low nitrogen tolerance

Over evolutionary time, plants have developed sophisticated regulatory mechanisms to adapt to fluctuating nitrogen (N) environments, ensuring that their growth is balanced with their responses to N stress. This study explored the potential of L-tryptophan (Trp) in regulating sorghum root growth under conditions of N limitation. Here, two distinct sorghum genotypes (low-N tolerance 398B and low-N sensitive CS3541) were utilized for investigating effect of low-N stress on root morphology and conducting a comparative transcriptomics analysis. Our foundings indicated that 398B exhibited longer roots, greater root dry weights, and a higher Trp content compared to CS3541 under low-N conditions. Furthermore, transcriptome analysis revealed substantial differences in gene expression profiles related to Trp pathway and carbon (C) and N metabolism pathways between the two genotypes. Additional experiments were conducted to assess the effects of exogenous Trp treatment on the interplay between sorghum root growth and low-N tolerance. Our observations showed that Trp-treated plants developed longer root and had elevated levels of Trp and IAA under low-N conditons. Concurrently, these plants demonstrated stronger physiological activities in C and N metabolism when subjected to low-N stress. These results underscored the pivotal role of Trp on root growth and low-N stress responses by balancing IAA levels and C and N metabolism. This study not only deepens our understanding of how plants maintain growth plasticity during environmental stress but also provides valuable insights into the availability of amino acid in crops, which could be instrumental in developing strategies for promoting crop resilience to N deficiency.

Rhizosphere Mortierella strain of alfalfa exerted weed growth inhibition by inducing expression of plant hormone-related genes

Introduction

Weeds are significant factors that detrimentally affect crop health and hinder optimal herbage yield. Rhizosphere microorganisms play crucial roles in plant growth, development, and nutrient uptake. Therefore, research focusing on weed control through the lens of microorganisms has emerged as a prominent area of study. The oil-producing fungus Mortierella, which is known for its numerous agricultural benefits, has garnered significant attention in recent years.

Methods

In this study, we conducted inoculation experiments in a controlled artificial culture climate chamber to investigate the effects of differential hormones and differentially expressed genes in the stems and leaves of Digitaria sanguinalis using Liquid Chromatography Tandem Mass Spectrometry and RNA-seq techniques, respectively. Additionally, Pearson's correlation analysis was used to establish correlations between differential hormones and growth indicators of Digitaria sanguinalis.

Results and discussion

The results demonstrated that inoculation with Mortierella sp. MXBP304 effectively suppressed aboveground biomass and plant height in Digitaria sanguinalis. Furthermore, there was significant upregulation and downregulation in the expression of genes involved in the synthesis and metabolism of phenylalanine and L-phenylalanine. Conversely, the expression of genes related to tryptophan, L-tryptophan, and indole was significantly downregulated. The addition of Mortierella sp. MXBP304 can influence the gene expression associated with phenylalanine and tryptophan synthesis and metabolism during Digitaria sanguinalis growth, subsequently reducing the relative contents of phenylalanine and tryptophan, thereby directly inhibiting Digitaria sanguinalis growth.

A Molecular Dynamics Simulation Study of the Effects of βGln114 Mutation on the Dynamic Behavior of the Catalytic Site of the Tryptophan Synthase

L-tryptophan (l-Trp), a vital amino acid for the survival of various organisms, is synthesized by the enzyme tryptophan synthase (TS) in organisms such as eubacteria, archaebacteria, protista, fungi, and plantae. TS, a pyridoxal 5'-phosphate (PLP)-dependent enzyme, comprises α and β subunits that typically form an α2β2 tetramer. The enzyme's activity is regulated by the conformational switching of its α and β subunits between the open (T state) and closed (R state) conformations. Many microorganisms rely on TS for growth and replication, making the enzyme and the l-Trp biosynthetic pathway potential drug targets. For instance, Mycobacterium tuberculosis, Chlamydiae bacteria, Streptococcus pneumoniae, Francisella tularensis, Salmonella bacteria, and Cryptosporidium parasitic protozoa depend on l-Trp synthesis. Antibiotic-resistant salmonella strains have emerged, underscoring the need for novel drugs targeting the l-Trp biosynthetic pathway, especially for salmonella-related infections. A single amino acid mutation can significantly impact enzyme function, affecting stability, conformational dynamics, and active or allosteric sites. These changes influence interactions, catalytic activity, and protein-ligand/protein-protein interactions. This study focuses on the impact of mutating the βGln114 residue on the catalytic and allosteric sites of TS. Extensive molecular dynamics simulations were conducted on E(PLP), E(AEX1), E(A-A), and E(C3) forms of TS using the WT, βQ114A, and βQ114N versions. The results show that both the βQ114A and βQ114N mutations increase protein backbone root mean square deviation fluctuations, destabilizing all TS forms. Conformational and hydrogen bond analyses suggest the significance of βGln114 drifting away from cofactor/intermediates and forming hydrogen bonds with water molecules necessary for l-Trp biosynthesis. The βQ114A mutation creates a gap between βAla114 and cofactor/intermediates, hindering hydrogen bond formation due to short side chains and disrupting β-sites. Conversely, the βQ114N mutation positions βAsn114 closer to cofactor/intermediates, forming hydrogen bonds with O3 of cofactors/intermediates and nearby water molecules, potentially disrupting the l-Trp biosynthetic mechanism.

Multi-omics analysis reveals differential molecular responses to cadmium toxicity in rice root tip and mature zone

Cadmium (Cd) is a highly toxic heavy metal that can be readily absorbed by plants and enriched in human body. Rice (Oryza sativa L.) yield and grain quality are affected by excessive Cd in the soil. Therefore, understanding the mechanisms of Cd absorption, accumulation and detoxification in the root apex is crucial for developing low-Cd rice cultivars. After Cd treatment, Cd concentration in rice root tips (RT) was 1.4 times higher than that in basal roots (BR). To uncover the distinct molecular responses to Cd toxicity, we conducted transcriptomic, proteomic, and metabolomic analyses on the two root sections. The results revealed that the RT exhibited 1.2-2.0 fold higher transcript or protein abundance of several Cd-related transporters than the BR, including Nramp1, Nramp5, IRT1, and HMA3, thereby contributing to more Cd accumulation in the RT. Furthermore, multi-omics analysis unveiled that the RT had enhanced activity in 'phenylpropanoid metabolism', 'AsA-GSH cycle' and 'tryptophan metabolism', conferring the stronger antioxidant system. While the BR showed higher activation in 'cell wall remodeling' and 'terpenoid biosynthesis'. This comprehensive study provides insights into the regulatory network of genes, proteins and metabolites involved in the differential responses to Cd toxicity between rice root tips and mature zones.

Light-induced LLPS of the CRY2/SPA1/FIO1 complex regulating mRNA methylation and chlorophyll homeostasis in Arabidopsis

Light regulates chlorophyll homeostasis and photosynthesis via various molecular mechanisms in plants. The light regulation of transcription and protein stability of nuclear-encoded chloroplast proteins have been extensively studied, but how light regulation of mRNA metabolism affects abundance of nuclear-encoded chloroplast proteins and chlorophyll homeostasis remains poorly understood. Here we show that the blue light receptor cryptochrome 2 (CRY2) and the METTL16-type m6A writer FIONA1 (FIO1) regulate chlorophyll homeostasis in response to blue light. In contrast to the CRY2-mediated photo-condensation of the mRNA adenosine methylase (MTA), photoexcited CRY2 co-condenses FIO1 only in the presence of the CRY2-signalling protein SUPPRESSOR of PHYTOCHROME A (SPA1). CRY2 and SPA1 synergistically or additively activate the RNA methyltransferase activity of FIO1 in vitro, whereas CRY2 and FIO1, but not MTA, are required for the light-induced methylation and translation of the mRNAs encoding multiple chlorophyll homeostasis regulators in vivo. Our study demonstrates that the light-induced liquid-liquid phase separation of the photoreceptor/writer complexes is commonly involved in the regulation of photoresponsive changes of mRNA methylation, whereas the different photo-condensation mechanisms of the CRY/FIO1 and CRY/MTA complexes explain, at least partially, the writer-specific functions in plant photomorphogenesis.

Straw Mulch Induced Indoleamines Alleviate Reproductive Depression in Cold Sensitive Hazelnut Cultivars

Climate change is forcing physiological changes, especially in temperate trees, in which the reproduction phase has been affected harshly, eventually resulting in poor performance. Erratic fluctuations during the flowering periods, predominantly in cold-sensitive, yet industry-desired (sourced), hazelnut cultivars have been causing at least a 10-fold decline in the nut yield. Indoleamines have been noted to provide protection during such abiotic stress conditions. In this study, we investigated the potential involvement of the indoleamine pathway in countering reproductive depression in cold-sensitive hazelnuts by blanketing the ground with wheat straw mulch. The female flower ratio; titers of tryptophan, serotonin, and melatonin; and indoleamine pathway gene regulation were the endpoints for assessing the effects of straw mulch. In the preceding year, we noted that the occurrence of phenological events through the modulation of indoleamines was necessitated via percolation of snowmelt into the rootzone. Otherwise, reproductive depression was noted, especially in harsh conditions, such as 'no snow' or when the rootzone was covered with a plastic sheet to disallow water percolation. When cold-sensitive hazelnut cultivars that were subjected to such deleterious treatments in the preceding years' experiments were treated with straw mulch, the female flower ratio was unaffected and remained on par with that of the cold-hardy locally adapted cultivars. Tryptophan accumulation improved in the (cold-sensitive) sourced cultivars treated with straw mulch and was available as serotonin to counter the cold stress. Lower titers of melatonin explained the slight improvement in female ratio in the sourced cultivars blanketed with straw mulch. ASMT gene regulation via straw mulch treatment emphasized its role in abiotic stress mitigation. A negative trend was noted when improved flowering was compared to the decreased expression of the ASMT gene. Horticultural changes, such as mulch, should provide mitigating solutions to relieve reproductive depression in cold-sensitive hazelnuts, alongside implications in other horticultural crops. The indoleamine toolkit (cellular markers) developed in this study provides insights into the mechanisms of cold sensitivity (abiotic stress) and plausible solutions, such as exogenous application of indoleamines, to propagate climate resilient plant materials with an enhanced capacity to mitigate abiotic stress conditions.

Tryptophan pretreatment adjusts transcriptome and metabolome profiles to alleviate cadmium toxicity in Arabidopsis

Cadmium (Cd) is highly toxic to all organisms including plants, and recently tryptophan (Trp) pretreatment of plant seedlings is shown to improve Cd tolerance. But the underlying mechanism remains largely unknown. In this study, we used Arabidopsis (Arabidopsis thaliana) to determine the physiological relevance of Trp pretreatment in alleviating Cd toxicity in plants and explore its molecular mechanism with a focus on the metabolic pathways. The results showed that Trp pretreatment maintained the biomass and root lengths, relieved Cd-induced lipid peroxidation, and reduced Cd transport to the shoots, and eventually improved the response against Cd in Arabidopsis seedlings. The integrative analyses of the transcriptome and metabolome further revealed that Trp pretreatment alleviated Cd toxicity not only through a known mechanism of producing a major auxin indole-3-acetic acid and maintaining its levels, but also through two previously unrecognized mechanisms: increasing the area and strength of cell walls by promoting lignification to further reduce Cd entry, and fine-tuning Cd detoxification products derived from sulfur-containing amino acid metabolism. Our findings thereby provide deep mechanical insights into how Trp alleviates Cd toxicity in plants.

Chromosome-level genome and high nitrogen stress response of the widespread and ecologically important wetland plant Typha angustifolia

Typha angustifolia L., known as narrowleaf cattail, is widely distributed in Eurasia but has been introduced to North America. Typha angustifolia is a semi-aquatic, wetland obligate plant that is widely distributed in Eurasia and North America. It is ecologically important for nutrient cycling in wetlands where it occurs and is used in phytoremediation and traditional medicine. In order to construct a high-quality genome for Typha angustifolia and investigate genes in response to high nitrogen stress, we carried out complete genome sequencing and high-nitrogen-stress experiments. We generated a chromosomal-level genome of T. angustifolia, which had 15 pseudochromosomes, a size of 207 Mb, and a contig N50 length of 13.57 Mb. Genome duplication analyses detected no recent whole-genome duplication (WGD) event for T. angustifolia. An analysis of gene family expansion and contraction showed that T. angustifolia gained 1,310 genes and lost 1,426 genes. High-nitrogen-stress experiments showed that a high nitrogen level had a significant inhibitory effect on root growth and differential gene expression analyses using 24 samples found 128 differentially expressed genes (DEGs) between the nitrogen-treated and control groups. DEGs in the roots and leaves were enriched in alanines, aspartate, and glutamate metabolism, nitrogen metabolism, photosynthesis, phenylpropanoid biosynthesis, plant-pathogen interaction, and mitogen-activated protein kinase pathways, among others. This study provides genomic data for a medicinal and ecologically important herb and lays a theoretical foundation for plant-assisted water pollution remediation.

Cadmium tolerance in Elodea canadensis Michx: Subcellular distribution and metabolomic analysis

The aquatic plant Elodea canadensis is considered a good candidate for ecotoxicological investigations. Cadmium (Cd) is a widespread contaminant in aquatic systems. In this study, to better elucidate the underlying tolerance mechanism and molecular impact of environmentally relevant Cd concentration in aquatic plants, subcellular distribution, chemical forms, and gas chromatography-mass spectrometry-based non-targeted metabolomics profiles were comprehensively analyzed in E. canadensis subjected to 0 and 10 µM Cd treatment for 5 d. Subcellular fractionation analysis of Cd-containing leaves showed that 67% of Cd was compartmentalized in cell wall followed by the soluble fraction (24 %) and organelles (9 %). The majority of Cd (90 %) was found in the extraction using 1 M NaCl. Metabolomic analysis using unsupervised principal component analyses and a supervised partial least squares discriminant analysis revealed clear differences in metabolic profiles between the two groups, demonstrating the metabolic effects of Cd. The 155 identified compounds altered by Cd were mainly from primary metabolism, including sugars, amino acids, organic acids, and their derivatives. Secondary metabolites such as polyphenols and phenolamides were also detected. The massive up-regulation of metabolites, including trehalose, proline, sarcosine, nicotianamine, putrescine, α-ketoglutaric acid, citric acid, and phytol might represent a detoxification mechanism. These findings highlighted the mechanistic strategies that E. canadensis employs to defend against Cd toxicity.

Arabidopsis AtMSRB5 functions as a salt-stress protector for both Arabidopsis and rice

Salinity, drought and low temperature are major environmental factors that adversely affect crop productivity worldwide. In this study we adopted an activation tagging approach to identify salt tolerant mutants of Arabidopsis. Thousands of tagged Arabidopsis lines were screened to obtain several potential mutant lines resistant to 150 mM NaCl. Transcript analysis of a salt-stress tolerance 1 (sst1) mutant line indicated activation of AtMSRB5 and AtMSRB6 which encode methionine sulfoxide reductases. Overexpression of AtMSRB5 in Arabidopsis (B5OX) showed a similar salt tolerant phenotype. Furthermore, biochemical analysis indicated stability of the membrane protein, H+-ATPase 2 (AHA2) through regulation of Na+/K+ homeostasis which may be involved in a stress tolerance mechanism. Similarly, overexpression of AtMSRB5 in transgenic rice demonstrated a salt tolerant phenotype via the modulation of Na+/K+ homeostasis without a yield drag under salt and oxidative stress conditions.

Indoleamines Impart Abiotic Stress Tolerance and Improve Reproductive Traits in Hazelnuts

Hazelnuts have recently gathered tremendous attention due to the expansion of the confectionary industry. However, the sourced cultivars fail to perform in initial phase of cultivation as they enter bare survival mode due to changes in climatic zones, for example, Southern Ontario, where the climate is continental, as opposed to the milder climate in Europe and Turkey. Indoleamines have been shown to counter abiotic stress and modulate vegetative and reproductive development of plants. Here, we examined the effect of indoleamines on the flowering response of the dormant stem cuttings of sourced hazelnut cultivars in controlled environment chambers. The stem cuttings were exposed to sudden summer-like conditions (abiotic stress) and the female flower development was assessed in relation to endogenous indoleamine titers. The sourced cultivars responded well to serotonin treatment by producing more flowers compared to the controls or other treatments. The probability of buds resulting in female flowers was highest in the middle region of the stem cuttings. It is interesting to note that the tryptamine titers of the locally adapted, and N-acetyl serotonin titers of native hazelnut cultivars, provided the best explanation for adaptation to the stress environment. Titers of both compounds were compromised in the sourced cultivars which resorted mostly to serotonin concentrations to counter the stress. The indoleamines tool kit identified in this study could be deployed in assessing cultivars for stress adaptation attributes.

Changes in rhizospheric microbiome structure and soil metabolic function in response to continuous cucumber cultivation

With the increasing reliance on intensive arable agriculture, analysis of the problems associated with continuous cropping has become a global research focus. Here, high-throughput sequencing and nontargeted metabolomics were used to evaluate the responses of soil microbial community structure and soil metabolic function to continuous cucumber cultivation (from 1 to 18 years of continuous cultivation) in greenhouses. Continuous cucumber cropping resulted in increased soil nutrient concentrations, but decreased concentrations of available nutrients. The abundance of several bacterial genera associated with nutrient cycling, such as Bacillus and Sphingomonas, was reduced by continuous cucumber cultivation. The abundance of several beneficial fungal genera, including pathogen antagonists (e.g. Chaetomium, Mortierella, Aspergillus, and Penicillium), were found to gradually decrease in response to the increased duration of continuous cropping. 3-amino-2-naphthoic acid and L-valine increased initially and then decreased as the cropping continued, which were related to fatty acid metabolism and amino acid biosynthesis. We also confirmed a close association between microbial community structure and soil metabolites. This study linked the changes in microbial community structure and metabolites in the rhizosphere soil and provided new insights into soil-microbial interactions in continuous cucumber culture systems.

Untargeted LC-MS/MS-Based Metabolomic Profiling for the Edible and Medicinal Plant Salvia miltiorrhiza Under Different Levels of Cadmium Stress

Salvia miltiorrhiza, a medicinal and edible plant, has been extensively applied to treat cardiovascular diseases and chronic hepatitis. Cadmium (Cd) affects the quality of S. miltiorrhiza, posing serious threats to human health. To reveal the metabolic mechanisms of S. miltiorrhiza's resistance to Cd stress, metabolite changes in S. miltiorrhiza roots treated with 0 (CK), 25 (T1), 50 (T2) and 100 (T3) mg kg^-1 Cd by liquid chromatography coupled to mass spectrometry (LC-MS/MS) were investigated. A total of 305 metabolites were identified, and most of them were amino acids, organic acids and fatty acids, which contributed to the discrimination of CK from the Cd-treated groups. Among them, S. miltiorrhiza mainly upregulated o-tyrosine, chorismate and eudesmic acid in resistance to 25 mg kg^-1 Cd; DL-tryptophan, L-aspartic acid, L-proline and chorismite in resistance to 50 mg kg^-1 Cd; and L-proline, L-serine, L-histidine, eudesmic acid, and rosmarinic acid in resistance to 100 mg kg^-1 Cd. It mainly downregulated unsaturated fatty acids (e.g., oleic acid, linoleic acid) in resistance to 25, 50, and 100 mg kg^-1 Cd and upregulated saturated fatty acids (especially stearic acid) in resistance to 100 mg kg^-1 Cd. Biosynthesis of unsaturated fatty acids, isoquinoline alkaloid, betalain, aminoacyl-tRNA, and tyrosine metabolism were the significantly enriched metabolic pathways and the most important pathways involved in the Cd resistance of S. miltiorrhiza. These data elucidated the crucial metabolic mechanisms involved in S. miltiorrhiza Cd resistance and the crucial metabolites that could be used to improve resistance to Cd stress in medicinal plant breeding.

The AP2/ERF transcription factor SlERF.F5 functions in leaf senescence in tomato

Our results confirmed that SlERF.F5 can directly regulate the promoter activity of ACS6 and interact with SlMYC2 to regulate tomato leaf senescence. The process of plant senescence is complex and highly coordinated, and is regulated by many endogenous and environmental signals. Ethylene and jasmonic acid are well-known senescence inducers, but their molecular mechanisms for inducing leaf senescence have not been fully elucidated. Here, we isolated an ETHYLENE RESPONSE FACTOR F5 (SlERF.F5) from tomato. Silencing of SlERF.F5 causes accelerated senescence induced by age, darkness, ethylene, and jasmonic acid. However, overexpression of SlERF.F5 would not promote senescence. Moreover, SlERF.F5 can regulate the promoter activity of ACS6 in vitro and in vivo. Suppression of SlERF.F5 resulted in increased sensitivity to ethylene and jasmonic acid, decreased accumulation of chlorophyll content, and inhibited the expression of chlorophyll- and light response-related genes. Compared with the wild type, the qRT-PCR analysis showed the expression levels of genes related to the ethylene biosynthesis pathway and the jasmonic acid signaling pathway in SlERF.F5-RNAi lines increased. Yeast two-hybrid experiments showed that SlERF.F5 and SlMYC2 (a transcription factor downstream of the JA receptor) can interact physically, thereby mediating the role of SlERF.F5 in jasmonic acid-induced leaf senescence. Collectively, our research provides new insights into how ethylene and jasmonic acid promote leaf senescence in tomato.

Heavy metal transporters: Functional mechanisms, regulation, and application in phytoremediation

Heavy metal pollution in soil is a global problem with serious impacts on human health and ecological security. Phytoextraction in phytoremediation, in which plants uptake and transport heavy metals (HMs) to the tissues of aerial parts, is the most environmentally friendly method to reduce the total amount of HMs in soil and has wide application prospects. However, the molecular mechanism of phytoextraction is still under investigation. The uptake, translocation, and retention of HMs in plants are mainly mediated by a variety of transporter proteins. A better understanding of the accumulation strategy of HMs via transporters in plants is a prerequisite for the improvement of phytoextraction. In this review, the biochemical structure and functions of HM transporter families in plants are systematically summarized, with emphasis on their roles in phytoremediation. The accumulation mechanism and regulatory pathways related to hormones, regulators, and reactive oxygen species (ROS) of HMs concerning these transporters are described in detail. Scientific efforts and practices for phytoremediation carried out in recent years suggest that creation of hyperaccumulators by transgenic or gene editing techniques targeted to these transporters and their regulators is the ultimate powerful path for the phytoremediation of HM contaminated soils.

The changes in Lemna minor metabolomic profile: A response to diclofenac incubation

Metabolomics is an emerging approach that investigates the changes in the metabolome profile. In the present study, Lemna minor -considered as an experimental aquatic plant model- was incubated with 10 and 100 μM diclofenac (DCF) for 96 h, respectively. Knowing that DCF is internationally often problematic in wastewater effluents and that it might affect particularly the metabolic profiles in aquatic plants, mainly the oxidoreductase, dehydrogenase, peroxidase, and glutathione reductase activities, here it was hypothesized (H) that in the common duckweed, DCF might increase the phenolic and flavonoids pathways, as an antioxidant response to this stress (H1). Also, it was expected DCF to alternate the physiological characteristics, especially the molecular interaction and biochemical properties, of Lemna (H2). Metabolic changes were investigated with target and untargeted screening analysis using RPLC-HILIC-ESI-TOF-MS. Twelve amino acids were identified in all treatments, together with three organic acids (p-coumaric, cinnamic, and sinapic acids). In untargeted screening, the important metabolites to discriminate between different treatments were assigned to Lemna such as organic acids, lignin, sugars, amino acids, dipeptides, flavonoids, biflavonoids, fatty acids, among others. In resume, Lemna responded to both DCF concentrations, showing different stress patterns. A similar metabolic response had already been identified in other studies in exposing Lemna to other anthropogenic stressors (like pesticides).

Early gene expression response of barley root tip to toxic concentrations of cadmium

Already a short-term Cd treatment induces changes in gene expression in barley root tips via IAA and ROS signaling during mild and severe Cd stress, respectively. Even a short, 30 min, Cd treatment of roots induced a considerable alteration in gene expression in the barley root tips within an hour after the treatments. The very early activation of MYB1 transcription factor expression is partially regulated by auxin signaling in mildly stressed seedlings. An increase in allene oxide cyclase and NADPH oxidase expression was a distinguishing feature of root tips response to mild Cd stress and their expression is activated via IAA signaling. Meanwhile, early changes in the level of dehydrin transcripts were detected in moderately and severely stressed root tips, and their induction is related to altered ROS homeostasis in cells. The early activation of glutathione peroxidase expression by mild Cd stress indicates the involvement of IAA in the signaling process. In contrast, early ascorbate peroxidase expression was induced only with Cd treatment causing severe stress and ROS play central roles in its induction. The expression of cysteine protease was activated similarly in both mildly and severely Cd-stressed roots; consequently, both increased IAA and ROS levels take part in the regulation of cysteine protease expression. The Cd-evoked accumulation of BAX Inhibitor-1 mRNA was characteristic for moderately and severely stressed roots. Whereas decreased IAA level did not affect its expression, rotenone-mediated ROS depletion markedly reduced the Cd-induced expression of BAX Inhibitor-1. An early increase of alternative oxidase levels in the root tip cells indicated that the reduction of mitochondrial superoxide generation is an important component of barley root response to severe Cd stress.

Metabolomics combined with physiology and transcriptomics reveals how Citrus grandis leaves cope with copper-toxicity

Limited data are available on metabolic responses of plants to copper (Cu)-toxicity. Firstly, we investigated Cu-toxic effects on metabolomics, the levels of free amino acids, NH₄⁺-N, NO₃^--N, total nitrogen, total soluble proteins, total phenolics, lignin, reduced glutathione (GSH) and malondialdehyde, and the activities of nitrogen-assimilatory enzymes in 'Shatian' pummelo (Citrus grandis) leaves. Then, a conjoint analysis of metabolomics, physiology and transcriptomics was performed. Herein, 59 upregulated [30 primary metabolites (PMs) and 29 secondary metabolites (SMs)] and 52 downregulated (31 PMs and 21 SMs) metabolites were identified in Cu-toxic leaves. The toxicity of Cu to leaves was related to the Cu-induced accumulation of NH₄⁺ and decrease of nitrogen assimilation. Metabolomics combined with physiology and transcriptomics revealed some adaptive responses of C. grandis leaves to Cu-toxicity, including (a) enhancing tryptophan metabolism and the levels of some amino acids and derivatives (tryptophan, phenylalanine, 5-hydroxy-l-tryptophan, 5-oxoproline and GSH); (b) increasing the accumulation of carbohydrates and alcohols and upregulating tricarboxylic acid cycle and the levels of some organic acids and derivatives (chlorogenic acid, quinic acid, d-tartaric acid and gallic acid o-hexoside); (c) reducing phospholipid (lysophosphatidylcholine and lysophosphatidylethanolamine) levels, increasing non-phosphate containing lipid [monoacylglycerol ester (acyl 18:2) isomer 1] levels, and inducing low-phosphate-responsive gene expression; and (d) triggering the biosynthesis of some chelators (total phenolics, lignin, l-trytamine, indole, eriodictyol C-hexoside, quercetin 5-O-malonylhexosyl-hexoside, N-caffeoyl agmatine, N'-p-coumaroyl agmatine, hydroxy-methoxycinnamate and protocatechuic acid o-glucoside) and vitamins and derivatives (nicotinic acid-hexoside, B₁ and methyl nicotinate). Cu-induced upregulation of many antioxidants could not protect Cu-toxic leaves from oxidative damage. To conclude, our findings corroborated the hypothesis that extensive reprogramming of metabolites was carried out in Cu-toxic C. grandis leaves in order to cope with Cu-toxicity.

Comprehensive Evaluation of Amino Acids and Polyphenols in 69 Varieties of Green Cabbage (Brassica oleracea L. var. capitata L.) Based on Multivariate Statistical Analysis

The biological activities of the primary metabolites and secondary metabolites of 69 green cabbage varieties were tested. The LC-MS detection method was used to determine the content of 19 free amino acids (lysine, tryptophan, phenylalanine, methionine, threonine, isoleucine, leucine, valine, arginine, asparagine, glycine, proline, tyrosine, glutamine, alanine, aspartic acid, serine, and glutamate). The content of 10 polyphenols (chlorogenic acid, gallic acid, 4-coumaric acid, ferulic acid, gentisic acid, cymarin, erucic acid, benzoic acid, rutin, and kaempferol) was determined by the HPLC detection method. Considering the complexity of the data obtained, variance analysis, diversity analysis, correlation analysis, hierarchical cluster analysis (HCA), and principal component analysis (PCA) were used to process and correlate amino acid or polyphenol data, respectively. The results showed that there were significant differences between the different amino acids and polyphenols of the 69 cabbage varieties. The most abundant amino acids and polyphenols were Glu and rutin, respectively. Both amino acids and polyphenols had a high genetic diversity, and multiple groups of significant or extremely significant correlations. The 69 cabbage varieties were divided into two groups, according to 19 amino acid indexes, by PCA. Among them, seven varieties with high amino acid content all fell into the fourth quadrant. The HCA of amino acids also supports this view. Based on 10 polyphenols, the 69 cabbage varieties were divided into two groups by HCA. Based on 29 indexes of amino acids and polyphenols, 69 cabbage varieties were evaluated and ranked by PCA. Therefore, in this study, cabbage varieties were classified in accordance with the level of amino acids and polyphenols, which provided a theoretical basis for the genetic improvement of nutritional quality in cabbage.

Medical Plant Extract Purification from Cadmium(II) Using Modified Thermoplastic Starch and Ion Exchangers

Pure compounds extracted and purified from medical plants are crucial for preparation of the herbal products applied in many countries as drugs for the treatment of diseases all over the world. Such products should be free from toxic heavy metals; therefore, their elimination or removal in all steps of production is very important. Hence, the purpose of this paper was purification of an extract obtained from Dendrobium officinale Kimura et Migo and cadmium removal using thermoplastic starch (S1), modified TPS with poly (butylene succinate); 25% of TPS + 75% PBS (S2); 50% of TPS + 50% PLA (S3); and 50% of TPS + 50% PLA with 5% of hemp fibers (S4), as well as ion exchangers of different types, e.g., Lewatit SP112, Purolite S940, Amberlite IRC747, Amberlite IRC748, Amberlite IRC718, Lewatit TP207, Lewatit TP208, and Purolite S930. This extract is used in cancer treatment in traditional Chinese medicine (TCM). Attenuated total reflectance-Fourier transform infrared spectroscopy, thermogravimetric analysis with differential scanning calorimetry, X-ray powder diffraction, gel permeation chromatography, surface analysis, scanning electron microscopy with energy dispersive X-ray spectroscopy, and point of zero charge analysis were used for sorbent and adsorption process characterization, as well as for explanation of the Cd(II) sorption mechanism.

A curated list of genes that affect the plant ionome

Understanding the mechanisms underlying plants' adaptation to their environment will require knowledge of the genes and alleles underlying elemental composition. Modern genetics is capable of quickly, and cheaply indicating which regions of DNA are associated with particular phenotypes in question, but most genes remain poorly annotated, hindering the identification of candidate genes. To help identify candidate genes underlying elemental accumulations, we have created the known ionome gene (KIG) list: a curated collection of genes experimentally shown to change uptake, accumulation, and distribution of elements. We have also created an automated computational pipeline to generate lists of KIG orthologs in other plant species using the PhytoMine database. The current version of KIG consists of 176 known genes covering 5 species, 23 elements, and their 1588 orthologs in 10 species. Analysis of the known genes demonstrated that most were identified in the model plant Arabidopsis thaliana, and that transporter coding genes and genes altering the accumulation of iron and zinc are overrepresented in the current list.

Indole-3-butyric acid priming reduced cadmium toxicity in barley root tip via NO generation and enhanced glutathione peroxidase activity

Activation of GPX and enhanced NO level play a key role in IBA-mediated enhanced Cd tolerance in young barley roots. Application of exogenous indole-3-acetic acid (IAA) or an IAA precursor improves the tolerance of plants to heavy metals. However, the physiology of these tolerance mechanisms remains largely unknown. Therefore, we studied the priming effect of indole-3-butyric acid (IBA), an IAA precursor, on mild and severe cadmium (Cd) stress-induced responses in roots of young barley seedlings. IBA, similarly to mild Cd stress, significantly increased the glutathione peroxidase (GPX) activity in the apexes of barley roots, which remained elevated after the IBA pretreatment as well. IBA pretreatment-evoked high nitric oxide generation in roots effectively reduced the high superoxide level under the severe Cd stress, leading to less toxic peroxynitrite accumulation accompanied by markedly reduced Cd-induced cell death. On the other hand, the IBA-evoked changes in IAA homeostasis resulted in root growth reorientation from longitudinal elongation to radial swelling. However, the application of an IAA signaling inhibitor, following the activation of defense responses by IBA, was able to promote root growth even at high concentrations of Cd. Based on the results, it can be concluded that the application of IBA, as an effective activator of Cd tolerance mechanisms in young barley roots, and the subsequent use of an IAA signaling inhibitor for the inhibition of root morphogenic responses induced by altered auxin metabolism, results in a high degree of root Cd tolerance, helping it to withstand even the transient exposure to lethal Cd concentration without the absolute inhibition of root growth.

Metabolomics reveals the "Invisible" detoxification mechanisms of Amaranthus hypochondriacus at three ages upon exposure to different levels of cadmium

To decipher the Cd hyperaccumulation and tolerance mechanisms of plants and increase phytoremediation efficiency, in this study, the physiological effects induced by environmentally relevant concentrations (0, 25 and 200 mg/kg) of Cd were characterized in Amaranthus hypochondriacus (K472) at three growth stages using LC/MS-based metabolomics. Metabolomic analysis identified 31, 29 and 30 significantly differential metabolites (SDMs) in K472 exposed to Cd at the early, intermediate and late stages of vegetative growth, respectively. These SDMs are involved in nine metabolic pathways responsible for antioxidation, osmotic balance regulation, energy supplementation and the promotion of metabolites that participate in phytochelatin (PC) synthesis. K472 at the intermediate stage of vegetative growth had the strongest tolerance to Cd with the combined action of Ala, Asp and Glu metabolism, purine metabolism, Gly, Ser and Thr metabolism and Pro and Arg metabolism. Among these crucial metabolic biomarkers, purine metabolism could be the primary regulatory target for increasing the Cd absorption of K472 for the restoration of Cd-contaminated soil.

Overexpressing broccoli tryptophan biosynthetic genes BoTSB1 and BoTSB2 promotes biosynthesis of IAA and indole glucosinolates

Tryptophan is one of the amino acids that cannot be produced in humans and has to be acquired primarily from plants. In Arabidopsis thaliana (Arabidopsis), the tryptophan synthase beta subunit (TSB) genes have been found to catalyze the biosynthesis of tryptophan. Here, we report the isolation and characterization of two TSB genes from Brassica oleracea (broccoli), designated BoTSB1 and BoTSB2. Overexpressing BoTSB1 or BoTSB2 in Arabidopsis resulted in higher tryptophan content and the accumulation of indole-3-acetic acid (IAA) and indole glucosinolates in rosette leaves. Therefore, the transgenic plants showed a series of high auxin phenotypes, including long hypocotyls, large plants and a high number of lateral roots. The spatial expression of BoTSB1 and BoTSB2 was detected by quantitative real-time PCR in broccoli and by expressing the β-glucuronidase reporter gene (GUS) controlled by the promoters of the two genes in Arabidopsis. BoTSB1 was abundantly expressed in vascular tissue of shoots and inflorescences. Compared to BoTSB1, BoTSB2 was expressed at a very low level in shoots but at a higher level in roots. We further investigated the expression response of the two genes to several hormone and stress treatments. Both genes were induced by methyl jasmonate (MeJA), salicylic acid (SA), gibberellic acid (GA), Flg22 (a conserved 22-amino acid peptide derived from bacterial flagellin), wounding, low temperature and NaCl and were repressed by IAA. Our study enhances the understanding of tryptophan biosynthesis and its regulation in broccoli and Arabidopsis. In addition, we provide evidence that TSB genes can potentially be a good tool to breed plants with high biomass and high nutrition.

Temperature alters susceptibility of Picea abies seedlings to airborne pollutants: The case of CdO nanoparticles

Although plants are often exposed to atmospheric nanoparticles (NPs), the mechanism of NP deposition and their effects on physiology and metabolism, and particularly in combination with other stressors, are not yet understood. Exploring interactions between stressors is particularly important for understanding plant responses in urban environments where elevated temperatures can be associated with air pollution. Accordingly, 3-year-old spruce seedlings were exposed for 2 weeks to aerial cadmium oxide (CdO) NPs of environmentally relevant size (8-62 nm) and concentration (2 × 10⁵ cm^-3). While half the seedlings were initially acclimated to high temperature (35 °C) and vapour pressure deficit (VPD; 2.81 kPa), the second half of the plants were left under non-stressed conditions (20 °C, 0.58 kPa). Atomic absorption spectrometry was used to determine Cd content in needles, while gas and liquid chromatography was used to determine changes in primary and secondary metabolites. Photosynthesis-related processes were explored with gas-exchange and chlorophyll fluorescence systems. Our work supports the hypothesis that atmospheric CdO NPs penetrate into leaves but high temperature and VPD reduce such penetration due to stomatal closure. The hypothesis that atmospheric CdO NPs influences physiological and metabolic processes in plants was also confirmed. This impact strengthens with increasing time of exposure. Finally, we found evidence that plants acclimated to stress conditions have different sensitivity to CdO NPs compared to plants not so acclimated. These findings have important consequences for understanding impacts of global warming on plants and indicates that although the effects of elevated temperatures can be deleterious, this may limit other forms of plant stress associated with air pollution.

Characteristic early membrane effects induced by tryptophan in pulvinar motor cells

Tryptophan at concentrations higher than 0.1 mM, triggered characteristic early physiological effects such as rapid (within 5 min) dose-dependent membrane hyperpolarization in Mimosa pudica motor cells and modification of the time course of the spontaneous proton efflux monitored in the incubation medium of pulvinar tissues. The rapid modifications of the leaf turgor-mediated movements seen on the primary pulvini of M. pudica following a shock and on Cassia fasciculata leaflets during a transition from light to darkness indicate that tryptophan disturbed the ionic migrations involved in the electrophysiological events and in the osmocontractile reaction of the motor cells. These reactions were specific to tryptophan compared to those induced by serine and 5-hydroxytryptophan. The tryptophan mode of action cannot be linked to a direct modification of the plasma membrane H⁺-ATPase activity as monitored on purified pulvinar plasma membrane vesicles. The tryptophan metabolism-linked products tryptamine and indole also inhibited the motile reactions, activated in a continuous manner the H⁺ secretion of pulvinar tissues and showed properties of a protonophore and an ATPase activity inhibitor on plasma membrane vesicles, respectively. The specific behavior of tryptophan in the reaction studies here is discussed in light of the previously reported action of phytohormones.

Abscisic acid, cold and salt stimulate conserved metabolic regulation in the moss Physcomitrella patens

Salt and cold are major abiotic stresses that have adverse effects on plant growth and development. To cope with these stresses and their detrimental effects plants have evolved several metabolic, biochemical and physiological processes that are mainly triggered and mediated by the plant hormone abscisic acid (ABA). To elucidate the metabolic responses of the moss Physcomitrella patens, which serves as a model plant for abiotic stress adaptation, we performed GC-MS-based metabolic profiling of plants challenged for 5 and 28 h with either salt, cold or ABA. Our results indicate significant changes in the accumulation of several sugars including maltose, isomaltose and trehalose, amino acids including arginine, histidine, ornithine, tryptophan and tyrosine, and organic acids mainly citric acid and malonic acid. The metabolic responses provoked by ABA, cold and salt show considerable similarities. The accumulation of certain metabolites positively correlates with gene expression data whereas some metabolites do not show correlation with cognate transcript abundance. To place our results into an evolutionary context we compared the ABA- and stress-induced metabolic changes in moss to available metabolic profiles of the seed plant Arabidopsis thaliana. We detected considerable conservation between the species, indicating early evolution of stress-associated metabolic adaptations that probably occurred at the plant water-to-land transition.

Effects of cadmium stress on growth and amino acid metabolism in two Compositae plants

Cadmium, a high toxic heavy metal, is one of the most serious contaminants in soil and a potential threat to plant growth and human health. Amino acid metabolism has the central role in heavy metal stress resistance of plants. In this paper, a pot experiment was carried out to study the effects of different concentrations of cadmium (0, 3, 6, 12, 30 mg kg^-1) on the growth, Cd accumulation and amino acid metabolism in two Compositae plants (Ageratum conyzoides L. and Crassocephalum crepidioides). The results showed that under cadmium stress, C. crepidioides accumulated more Cd in its shoot and was tolerant to Cd, whereas its low Cd-accumulating relative, A. conyzoides, suffered reduced growth. The Cd content in the aerial part of C. crepidioides exceeded the threshold of Cd-hyperaccumulator. Furthermore, the bioaccumulation factor (BCF) and biological transfer factor (BTF) values for Cd in C. crepidioides were > 1. Thus, C. crepidioides can be regarded as Cd-hyperaccumulator. The comparison between both studied plants indicated that Cd stress resulted in a differential but coordinated response of amino acid levels, which are playing a significant role in plant adaptation to Cd stress. Glu, Gln, Asp, Asn, Gaba, Val and Ala dominated the major amino acids. Higher Cd tolerance and Cd accumulation in C. crepidioides was associated with greater accumulation of free amino acids, especially for Gln and Asn, in C. crepidioides than in A. conyzoides.

Maize similar to RCD1 gene induced by salt enhances Arabidopsis thaliana abiotic stress resistance

Plant SRO (SIMILAR TO RCD-ONE) proteins play important roles in regulating oxidation and metal ion metabolism. Numbers of SRO proteins have been functional identified in Arabidopsis and rice, but little is known in maize. In this study, we identified a salt induced SRO gene, ZmSRO1b, from maize and analyzed its characteristics. ZmSRO1b expressed mainly in leaf tissues. The ZmSRO1b is encoded by 595 amino acid residues and shared conserved protein models with AtRCD1 and AtSRO1 from Arabidopsis. Promoter-elements analysis showed ZmSRO1b promoter harbored salt and metal stress responsive elements, DRE, GT-like and MRE. Further promoter inductive analysis by GUS staining and quantification confirmed that ZmSRO1b promoter was induced by salt and cadmium (Cd). Methylviologen (MV) simulated oxidative stress showed ZmSRO1b promoter was also induced by MV. Overexpression of ZmSRO1b in Arabidopsis plants showed increased resistance to salt, Cd and oxidative stress. Our results for the first time experimentally validate the function of ZmSRO1b and contribute to the better understanding of SRO genes across different plant species.

The phytotoxicities of decabromodiphenyl ether (BDE-209) to different rice cultivars (Oryza sativa L.)

Decabromodiphenyl ether (BDE-209), as a major component of brominated flame retardants, has been detected in the agricultural soil in considerable amount. Given that BDE-209 is toxic, ubiquitous and persistent, BDE-209 might induce toxic effects on rice cultivars planted in contaminated soil. A comparative study was conducted on phytotoxicities and GC-MS based antioxidant-related metabolite levels to investigate the differences of phytotoxicities of BDE-209 to rice cultivars in Yangtze River Delta of China. Rice seedlings were treated with BDE-209 at 0, 10, 50, 100 and 500 μg/L in a hydroponic setup. Results showed that BDE-209-induced phytotoxicites were cultivar-dependent and that the antioxidant defense systems in the cultivars were disturbed differently. Among the three selected cultivars (Jiayou 5, Lianjing 7 and Yongyou 9), Jiayou 5 and Lianjing 7 displayed lower toxic effects than Yongyou 9 in terms of the growth inhibition, lipid peroxidation and DNA damage. The increases of antioxidant enzymes were significantly higher in Jiayou 5 and Lianjing 7 than those in Yongyou 9. Multivariate analysis of antioxidant-related metabolites in the three cultivars indicated that l-tryptophan and l-valine were the most important ones among 10 metabolites responsible for the separation of cultivars. The up-regulation of l-tryptophan and l-valine were likely plant strategies to increase their tolerance. The current results provided an insight into the development of rice cultivars with higher BDE-209 tolerance.

Plant responses to environmental stresses-from gene to biotechnology

Increasing global population, urbanization and industrialization are increasing the rate of conversion of arable land into wasteland. Supplying food to an ever-increasing population is one of the biggest challenges that agriculturalists and plant scientists are currently confronting. Environmental stresses make this situation even graver. Despite the induction of several tolerance mechanisms, sensitive plants often fail to survive under environmental extremes. New technological approaches are imperative. Conventional breeding methods have a limited potential to improve plant genomes against environmental stress. Recently, genetic engineering has contributed enormously to the development of genetically modified varieties of different crops such as cotton, maize, rice, canola and soybean. The identification of stress-responsive genes and their subsequent introgression or overexpression within sensitive crop species are now being widely carried out by plant scientists. Engineering of important tolerance pathways, like antioxidant enzymes, osmolyte accumulation, membrane-localized transporters for efficient compartmentation of deleterious ions and accumulation of essential elements and resistance against pests or pathogens is also an area that has been intensively researched. In this review, the role of biotechnology and its successes, prospects and challenges in developing stress-tolerant crop cultivars are discussed.

Cadmium toxicity induced contrasting patterns of concentrations of free sarcosine, specific amino acids and selected microelements in two Noccaea species

Cadmium (Cd) toxicity affects numerous metabolic processes in plants. In the presence of Cd, plants accumulate specific amino acids which may be beneficial to developing Cd tolerance. Our study aimed to characterize the changes in the metabolism of selected free amino acids that are associated with Cd tolerance, and investigate the levels of selected microelements in order to relate these changes to the adaptation strategies of two metallophytes-Noccaea caerulescens (Redlschlag, Austria) and Noccaea praecox (Mežica, Slovenia). The plants were exposed to Cd contamination (90 mg Cd/kg soil) for 120 days in a pot experiment. Our results showed higher Cd accumulation in N. praecox compared to N. caerulescens. Cadmium contamination reduced the zinc and nickel levels in both species and a mixed effect was determined for copper and manganese content. Differences in free amino acid metabolism were observed between the two metallophytes growing under Cd-free and Cd-loaded conditions. Under Cd-free conditions, aromatic amino acids (phenylalanine, tryptophan and tyrosine) and branched-chain amino acids (leucine, isoleucine and valine) were accumulated more in the leaves of N. praecox than in N. caerulescens. Cd stress increased the content of these amino acids in both species but this increase was significant only in N. caerulescens leaves. Marked differences in the responses of the two species to Cd stress were shown for alanine, phenylalanine, threonine and sarcosine. Cadmium contamination also induced an increase of threonine as alanine and sarcosine decrease, which was larger in N. caerulescens than in N. praecox. All these factors contribute to the higher adaptation of N. praecox to Cd stress.

Changes of primary and secondary metabolites in barley plants exposed to CdO nanoparticles

The environmental fate of airborne nanoparticles and their toxicity to plants is not yet fully understood. Pot-grown barley plants with second leaves developed were therefore exposed to CdO nanoparticles (CdONPs) of ecologically relevant size (7-60 nm) and concentration (2.03 ± 0.45 × 10⁵ particles cm^-3) in air for 3 weeks. An experiment was designed to test the effects of different treatments when only leaves (T1); leaves and soil substrate (T2); and leaves, soil, and water supply were exposed to nanoparticles (T3). A fourth, control group of plants was left without treatment (T0). Although CdONPs were directly absorbed by leaves from the air, a part of leaf-allocated Cd was also transported from roots by transpiration flow. Chromatographic assays revealed that CdONPs had a significant effect on total content of primary metabolites (amino acids and saccharides) but no significant effect on total content of secondary metabolites (phenolic compounds, Krebs cycle acids, and fatty acids). In addition, the compositions of individual metabolite classes were affected by CdONP treatment. For example, tryptophan and phenylalanine were the most affected amino acids in both analysed organs, while ferulic acid and isovitexin constituted the polyphenols most affected in leaves. Even though CdONP treatment had no effect on total fatty acids content, there were significant changes in the composition of saturated and unsaturated fatty acids in both the roots and leaves of treated plants. Although the results indicate the most pronounced effect in T3 plants as compared to T1 and T2 plants, even just leaf exposure to CdONPs has the potential to induce changes in plant metabolism.

Bean metal-responsive element-binding transcription factor confers cadmium resistance in tobacco

Cadmium (Cd) is highly toxic to plants. Modulation of Cd-responsive transcription is an important way for Cd detoxification in plants. Metal-responsive element (MRE) is originally described in animal metallothionein genes. Although functional MREs also exist in Cd-regulated plant genes, specific transcription factors that bind MRE to regulate Cd tolerance have not been identified. Previously, we showed that Cd-inducible bean (Phaseolus vulgaris) stress-related gene2 (PvSR2) produces a short (S) PvSR2 transcript (S-PvSR2) driven by an intronic promoter. Here, we demonstrate that S-PvSR2 encodes a bean MRE-binding transcription factor1 (PvMTF-1) that confers Cd tolerance in tobacco (Nicotiana tabacum). PvMTF-1 expression was up-regulated by Cd at the levels of RNA and protein. Importantly, expression of PvMTF-1 in tobacco enhanced Cd tolerance, indicating its role in regulating Cd resistance in planta. This was achieved through direct regulation of a feedback-insensitive Anthranilate Synthase α-2 chain gene (ASA2), which catalyzes the first step for tryptophan biosynthesis. In vitro and in vivo DNA-protein interaction studies further revealed that PvMTF-1 directly binds to the MRE in the ASA2 promoter, and this binding depends on the zinc finger-like motif of PvMTF-1. Through modulating ASA2 up-regulation by Cd, PvMTF-1 increased free tryptophan level and subsequently reduced Cd accumulation, thereby enhancing Cd tolerance of transgenic tobacco plants. Consistent with this observation, tobacco transiently overexpressing ASA2 also exhibited increased tolerance to Cd. We conclude that PvMTF-1 is a zinc finger-like transcription factor that links MRE to Cd resistance in transgenic tobacco through activation of tryptophan biosynthesis.

Comparative analysis of metabolic proteome variation in ascorbate-primed and unprimed wheat seeds during germination under salt stress

Seed priming with ascorbic acid improves salt tolerance in durum wheat. For understanding the potential mechanisms underlying this priming effect a gel-free shotgun proteomic analysis was performed comparing unprimed to ascorbate-primed wheat seed during germination under saline and non-saline conditions. Since seed germination is the result of interplay or cross-talk between embryo and embryo-surrounding tissues, we studied the variation of metabolic proteome in both tissues separately. 167 of 697 identified and 69 of 471 identified proteins increase or decrease in abundance significantly in response to priming and/or salinity compared to untreated, unstressed control in embryo and embryo-surrounding tissues, respectively. In untreated wheat embryo salt stress was accompanied by change in 129 proteins, most of which are belonging to metabolism, energy, disease/defense, protein destination and storage categories. Ascorbate pretreatment prevents and counteracts the effects of salinity upon most of these proteins and changes specifically the abundance of 35 others proteins, most of which are involved in metabolism, protein destination and storage categories. Hierarchical clustering analysis revealed three and two major clusters of protein expression in embryo and embryo-surrounding tissues, respectively. This study opens promising new avenues to understand priming-induced salt tolerance in plants.

BIOLOGICAL SIGNIFICANCE

To clearly understand how ascorbate-priming enhance the salt tolerance of durum wheat during germination, we performed for the first time a comparative shotgun proteomic analysis between unprimed and ascorbate-primed wheat seeds during germination under saline and non-saline conditions. Furthermore, since seed germination is the result of interplay or cross-talk between embryo and embryo-surrounding tissues we analyzed the variation of metabolic proteome in both tissues separately. 1168 proteins exhibiting greater molecular weight diversity (ranging from 5 to 258kDa) were identified. Among them, 167 and 69 proteins were increased or decreased in abundance significantly by priming and/or salinity as compared to control, in embryo and embryo-surrounding tissues respectively. Ascorbate pretreatment alleviates the effects of salinity upon most of these proteins, particularly those involved in metabolism, energy, disease/defense, protein destination and storage functions. Hierarchical clustering analysis revealed three and two major clusters of protein accumulation in embryo and embryo-surrounding tissues, respectively. These results may provide new avenues for understanding and advancing priming-induced salt tolerance in crop plants.

Transcriptome profiling and physiological studies reveal a major role for aromatic amino acids in mercury stress tolerance in rice seedlings

Mercury (Hg) is a serious environmental pollution threat to the planet. The accumulation of Hg in plants disrupts many cellular-level functions and inhibits growth and development, but the mechanism is not fully understood. To gain more insight into the cellular response to Hg, we performed a large-scale analysis of the rice transcriptome during Hg stress. Genes induced with short-term exposure represented functional categories of cell-wall formation, chemical detoxification, secondary metabolism, signal transduction and abiotic stress response. Moreover, Hg stress upregulated several genes involved in aromatic amino acids (Phe and Trp) and increased the level of free Phe and Trp content. Exogenous application of Phe and Trp to rice roots enhanced tolerance to Hg and effectively reduced Hg-induced production of reactive oxygen species. Hg induced calcium accumulation and activated mitogen-activated protein kinase. Further characterization of the Hg-responsive genes we identified may be helpful for better understanding the mechanisms of Hg in plants.

Morphological and proteomic responses of Eruca sativa exposed to silver nanoparticles or silver nitrate

Silver nanoparticles (AgNPs) are widely used in commercial products, and there are growing concerns about their impact on the environment. Information about the molecular interaction of AgNPs with plants is lacking. To increase our understanding of the mechanisms involved in plant responses to AgNPs and to differentiate between particle specific and ionic silver effects we determined the morphological and proteomic changes induced in Eruca sativa (commonly called rocket) in response to AgNPs or AgNO3. Seedlings were treated for 5 days with different concentrations of AgNPs or AgNO3. A similar increase in root elongation was observed when seedlings were exposed to 10 mg Ag L(1) of either PVP-AgNPs or AgNO3. At this concentration we performed electron microscopy investigations and 2-dimensional electrophoresis (2DE) proteomic profiling. The low level of overlap of differentially expressed proteins indicates that AgNPs and AgNO3 cause different plant responses. Both Ag treatments cause changes in proteins involved in the redox regulation and in the sulfur metabolism. These responses could play an important role to maintain cellular homeostasis. Only the AgNP exposure cause the alteration of some proteins related to the endoplasmic reticulum and vacuole indicating these two organelles as targets of the AgNPs action. These data add further evidences that the effects of AgNPs are not simply due to the release of Ag ions.

Trace elements present in airborne particulate matter--stressors of plant metabolism

Changes of amino acid concentrations (glutamic acid, glutamine, asparagine, aspartate, proline, tryptophan, alanine, glycine, valine and serine), gas-exchange parameters (net photosynthetic rate, transpiration rate, stomatal conductance and intercellular CO(2) concentration) and nitrate levels in Lactuca serriola L. under airborne particulate matter (PM) contamination reported here reveal their role in plant chronic stress adaptation. Results of the pot experiment confirmed the toxic effect of trace elements present in PM for lettuce. PM applied to soil or on the lettuce leaves were associated with the strong inhibition of above-ground biomass and with the enhancement of plant trace element contents. The significant changes of amino acid levels and leaf gas-exchange parameters of the plants showed strong linear dependences on PM contamination (R(2)=0.60-0.99). PM application on leaves intensified toxic effect of trace elements (As, Pb, Cr and Cd) originating from PM by shading of the leaf surface. The plant accumulation of nitrate nitrogen after PM contamination confirmed to block nitrate assimilation.

Cytogenetic response of Scots pine (Pinus sylvestris Linnaeus, 1753) (Pinaceae) to heavy metals

We studied cytogenetic reactions of Scots pine seedlings to heavy metals - lead, cupric and zinc nitrates applied at concentrations 0.5 to 2000 µM. We determined the range of concentrations of heavy metals that causes mutagenic effect. Lead was found to cause the strongest genotoxicity as manifested by significant increase in the frequency of pathological mitosis, occurrence of fragmentations and agglutinations of chromosomes, various types of bridges, and a significant number of the micronuclei which were absent in the control. Possible cytogenetic mechanisms of the cytotoxic action of heavy metals are discussed.

Ectopic expression of an EAR motif deletion mutant of SlERF3 enhances tolerance to salt stress and Ralstonia solanacearum in tomato

Ethylene-responsive transcription factors (ERFs) bind specifically to cis-acting DNA regulatory elements such as GCC boxes and play an important role in the regulation of defense- and stress-related genes in plants. In contrast to other ERFs, class II ERFs contain an ERF-associated amphiphilic repression (EAR) domain and act as GCC-mediated transcriptional repressors. In this study, SlERF3, a class II ERF was isolated from tomato and characterized. To examine whether the EAR motif of class II ERF proteins participates in ERF-mediated functions in plants, the EAR domain was deleted to generate SlERF3ΔRD. We show that SlERF3ΔRD protein retains the character of a transcription factor and becomes a GCC-mediated transcriptional activator. Constitutive expression of full-length SlERF3 in tomato severely suppressed growth and, as a result, no transgenic plants were obtained. However, no apparent effects on growth and development of SlERF3ΔRD transgenic plants were observed. Overexpression of SlERF3ΔRD in transgenic tomato induced expression of pathogenesis-related protein genes such as PR1, PR2 and PR5, and enhanced tolerance to Ralstonia solanacearum. Furthermore, transgenic Arabidopsis and tomatoes constitutively expressing SlERF3ΔRD exhibited reduced levels of membrane lipid peroxidation and enhanced tolerance to salt stress. In comparison with wild-type plants grown under stress conditions, transgenic SlERF3ΔRD tomatoes produced more flowers, fruits, and seeds. This study illustrates a gene-enhancing tolerance to both biotic and abiotic stresses in transgenic plants with the deletion of a repressor domain. Our findings suggest that class II ERF proteins may find important use in crop improvement or genetic engineering to increase stress tolerance in plants.

A tomato bZIP transcription factor, SlAREB, is involved in water deficit and salt stress response

Abiotic stresses such as cold, water deficit, and salt stresses severely reduce crop productivity. Tomato (Solanum lycopersicum) is an important economic crop; however, not much is known about its stress responses. To gain insight into stress-responsive gene regulation in tomato plants, we identified transcription factors from a tomato cDNA microarray. An ABA-responsive element binding protein (AREB) was identified and named SlAREB. In tomato protoplasts, SlAREB transiently transactivated luciferase reporter gene expression driven by AtRD29A (responsive to dehydration) and SlLAP (leucine aminopeptidase) promoters with exogenous ABA application, which was suppressed by the kinase inhibitor staurosporine, indicating that an ABA-dependent post-translational modification is required for the transactivation ability of SlAREB protein. Electrophoretic mobility shift assays showed that the recombinant DNA-binding domain of SlAREB protein is able to bind AtRD29A and SlLAP promoter regions. Constitutively expressed SlAREB increased tolerance to water deficit and high salinity stresses in both Arabidopsis and tomato plants, which maintained PSII and membrane integrities as well as water content in plant bodies. Overproduction of SlAREB in Arabidopsis thaliana and tomato plants regulated stress-related genes AtRD29A, AtCOR47, and SlCI7-like dehydrin under ABA and abiotic stress treatments. Taken together, these results show that SlAREB functions to regulate some stress-responsive genes and that its overproduction improves plant tolerance to water deficit and salt stress.