Alluminating structure key to stress tolerance

Plant tolerance to aluminium is encoded by root-localized aluminium-activated malate transporter 1 (ALMT1).In a recent study published in Cell Research,Wang et ...     

Temperature tolerance and stress proteins as mechanisms of invasive species success

Invasive species are predicted to be more successful than natives as temperatures increase with climate change. However, few studies have examined the physiological mechanisms that theoretically underlie this differential success. Because correlative evidence suggests that invasiveness is related to the width of a species' latitudinal range, it has been assumed--but largely untested--that range width predicts breadth of habitat temperatures and physiological thermotolerances. In this study, we use empirical data from a marine community as a case study to address the hypotheses that (1) geographic temperature range attributes are related to temperature tolerance, leading to greater eurythermality in invasive species, and (2) stress protein expression is a subcellular mechanism that could contribute to differences in thermotolerance. We examined three native and six invasive species common in the subtidal epibenthic communities of California, USA. We assessed thermotolerance by exposing individuals to temperatures between 14°C and 31°C and determining the temperature lethal to 50% of individuals (LT(50)) after a 24 hour exposure. We found a strong positive relationship between the LT(50) and both maximum habitat temperatures and the breadth of temperatures experience across the species' ranges. In addition, of the species in our study, invasives tended to inhabit broader habitat temperature ranges and higher maximum temperatures. Stress protein expression may contribute to these differences: the more thermotolerant, invasive species Diplosoma listerianum expressed higher levels of a 70-kDa heat-shock protein than the less thermotolerant, native Distaplia occidentalis for which levels declined sharply above the LT(50). Our data highlight differences between native and invasive species with respect to organismal and cellular temperature tolerances. Future studies should address, across a broader phylogenetic and ecosystem scope, whether this physiological mechanism has facilitated the current success of invasive species and could lead to greater success of invasives than native species as global warming continues.     

Relationship of species composition of tropical seagrass meadows to multiple physical environmental factors

The purpose of this study was to examine the relationship between species composition of tropical seagrasses and various physical environmental factors: depth, sediment thickness and silt–clay content in the sediments. We investigated species composition and abundance of seagrasses as well as the physical environmental factors for six transects around Ishigaki Island, southwest Japan. Eight species occurred in the quadrat census. The occurrence frequencies ranged from 66.8% (Thalassia hemprichii) to 4.5% (Enhalus acoroides). Both canonical correspondence analysis (CCA) and cluster analysis elucidated that depth was mainly responsible for the distributions of species and assemblage type. Monte Carlo permutation for partial CCA revealed that 37.5% of the variance was explained by depth, 10.3% by sediment thickness and 4.6% by silt–clay content in the sediment. Twenty-six sites were categorized into four assemblage types by a cluster analysis using the leaf area index (LAI; the ratio of total leaf area to bottom area) as a measure of species abundance. Type I was dominated by T. hemprichii and Cymodocea rotundata, Type II by C. serrulata, Type III by E. acoroides, and Type IV by Halodule pinifolia and Halophila ovalis. Type I occurred mostly in the intertidal zone (91.3±30.5 cm below MSL, mean sea level), Type II in the subtidal zone (179.1±75.0 cm below MSL) and Type IV in both shallow sites (between 47.8 and 75.6 cm below MSL) and in those with low silt–clay contents (between 2.0 and 3.8%).     

Allele mining for stress tolerance genes in Oryza species and related germplasm

Allele mining exploits the deoxyribonucleic acid (DNA) sequence of one genotype to isolate useful alleles from related genotypes. The international project to sequence the genome of Oryza sativa L cv. Nipponbare will make allele mining possible for all genes of rice and possibly related cereals. We used a rice calmodulin gene, a rice gene encoding a late embryogenesis-associated protein, and salt-inducible rice gene to optimize the polymerase chain reaction (PCR) for allele mining of stress tolerance genes on identified accessions of rice and related germplasm. Two sets of PCR primers were designed for each gene. Primers based on the 5′ and 3′ untranslated region of genes were found to be sufficiently conserved so as to be effective over the entire range of germplasm in rice for which the concept of allelism is applicable. However, the primers based on the adjacent amino (N) and carboxy (C) termini amplify additional loci.     

Life history adaptations and stress tolerance of four domestic species of Drosophila

Life history traits and stress tolerance were studied in four domestic species of Drosophila–D. melanogaster, D. simulans, D. auraria and D. immigrans– to understand how they adapt to their environments. In all species, larval weight approximately doubled in 1 day. The relative egg weight (egg weight : pupal weight) was smaller and the larval period was longer in D. immigrans than in the other three species. The pupal period was the longest in D. auraria. However, the adaptive significance of these differences in larval and pupal periods was not clear. The pupal case was generally thicker in the larger species, probably to support the larger pupal body. The start of oviposition was earliest and reproductive effort was greatest in female D. simulans, followed by female D. melanogaster. In contrast, starvation tolerance and the increase in bodyweight after eclosion was greater in D. immigrans and D. auraria than in the other two species. Pupal desiccation tolerance was greatest in D. melanogaster and lowest in D. auraria, and the less tolerant species seemed to select more humid sites for pupation. Adult tolerance to desiccation was greatest in D. melanogaster and lowest in D. simulans. In contrast, adult cold tolerance was greater in D. auraria and adult heat tolerance was lower in D. immigrans than in the other species. These differences in life history traits and stress tolerance represent the Drosophila species differential adaptations, and are assumed to allow coexistence of the species.     

Introduced species in seagrass ecosystems: Status and concerns

A literature review revealed that at least 56 non-native species, primarily invertebrates and seaweeds, have been introduced to seagrass beds, largely through shipping/boating activities and aquaculture. Four seagrass species also have been introduced. The introductions of the seaweeds Caulerpa taxifolia, C. racemosa v. cylindracea, Codium fragile ssp. tomentosoides, Sargassum muticum, the Asian mussel, Musculista senhousia, and the seagrass, Zostera japonica, are the best-known examples in seagrass beds. The ecological effects on seagrasses and associated communities have been examined for slightly less than half of the introduced species, which have predominantly negative effects. There is a paucity of experimental data for ecological effects, particularly for seagrass community structure and function. The exception to this finding is the introduction of the seagrass Z. japonica with oyster aquaculture to native eelgrass beds on the Pacific coasts of Canada and the USA. Recent experiments in several different seagrass ecosystems confirmed that disturbance contributes to the invasibility of seagrass beds. More definitive studies are required to elucidate the relative effects of nutrient pollution and introduced species in causing seagrass decline, particularly where reduced herbivory and boating activity also covary. Seagrass beds often are subject to multiple introduced species, but their cumulative effect has been virtually unstudied. The potential for compounded negative effects merits serious attention. Heightened attention to the issue of introduced species in seagrass beds is called for given the evidence that introduced species can contribute to seagrass decline, to biodiversity changes that could affect seagrass ecosystem functions, and that they can compromise seagrass restoration. Comprehensive surveys in seagrass beds, complemented by more stringent experimental and mensurative sampling designs, are needed. In the interim, conserving seagrass density and bed size can offer resistance to introduced species. Managing to prevent the introductions, including restricting transplantations of non-native biota during seagrass restorations, is likely to bear positive benefits for seagrass ecosystems.     

Concentration of MgSO4 in the intestinal lumen of Opsanus beta limits osmoregulation in response to acute hypersalinity stress

Marine teleosts constantly lose water to their surrounding environment, a problem exacerbated in fish exposed to salinity higher than normal seawater. Some fish undergo hypersaline exposures in their natural environments, such as short- and long-term increases in salinity occurring in small tidal pools and other isolated basins, lakes, or entire estuaries. Regardless of the degree of hypersalinity in the ambient water, intestinal absorption of monovalent ions drives water uptake to compensate for water loss, concentrating impermeable MgSO(4) in the lumen. This study considers the potential of luminal [MgSO(4)] to limit intestinal water absorption, and therefore osmoregulation, in hypersalinity. The overall tolerance and physiological response of toadfish (Opsanus beta) to hypersalinity exposure were examined. In vivo, fish in hypersaline waters containing artificially low [MgSO(4)] displayed significantly lower osmolality in both plasma and intestinal fluids, and increased survival at 85 parts per thousand, indicating improved osmoregulatory ability than in fish exposed to hypersalinity with ionic ratios similar to naturally occurring ratios. Intestinal sac preparations revealed that in addition to the osmotic pressure difference across the epithelium, the luminal ionic composition influenced the absorption of Na(+), Cl(-), and water. Hypersalinity exposure increased urine flow rates in fish fitted with ureteral catheters regardless of ionic composition of the ambient seawater, but it had no effect on urine osmolality or pH. Overall, concentrated MgSO(4) within the intestinal lumen, rather than renal or branchial factors, is the primary limitation for osmoregulation by toadfish in hypersaline environments.     

Reactive oxygen species and antioxidant machinery in abiotic stress tolerance in crop plants

Various abiotic stresses lead to the overproduction of reactive oxygen species (ROS) in plants which are highly reactive and toxic and cause damage to proteins, lipids, carbohydrates and DNA which ultimately results in oxidative stress. The ROS comprises both free radical (O₂^?, superoxide radicals; OH, hydroxyl radical; HO₂, perhydroxy radical and RO, alkoxy radicals) and non-radical (molecular) forms (H₂O₂, hydrogen peroxide and ¹O₂, singlet oxygen). In chloroplasts, photosystem I and II (PSI and PSII) are the major sites for the production of ¹O₂ and O₂^?. In mitochondria, complex I, ubiquinone and complex III of electron transport chain (ETC) are the major sites for the generation of O₂^?. The antioxidant defense machinery protects plants against oxidative stress damages. Plants possess very efficient enzymatic (superoxide dismutase, SOD; catalase, CAT; ascorbate peroxidase, APX; glutathione reductase, GR; monodehydroascorbate reductase, MDHAR; dehydroascorbate reductase, DHAR; glutathione peroxidase, GPX; guaicol peroxidase, GOPX and glutathione-S- transferase, GST) and non-enzymatic (ascorbic acid, ASH; glutathione, GSH; phenolic compounds, alkaloids, non-protein amino acids and α-tocopherols) antioxidant defense systems which work in concert to control the cascades of uncontrolled oxidation and protect plant cells from oxidative damage by scavenging of ROS. ROS also influence the expression of a number of genes and therefore control the many processes like growth, cell cycle, programmed cell death (PCD), abiotic stress responses, pathogen defense, systemic signaling and development. In this review, we describe the biochemistry of ROS and their production sites, and ROS scavenging antioxidant defense machinery.     

Drought stress tolerance of Prosopis chilensis and Prosopis flexuosa species and their hybrids

Natural hybridization commonly produces individuals with intermediate morphological and genetic characteristics, but their response to environmental stress is still uncertain, with some studies showing that transgressive performance would be common. Prosopis chilensis and Prosopis flexuosa are the most important tree species from Arid Chaco, South-America. Both species occupy different ecological niches in terms of water availability. Genetic and morphological studies have demonstrated the existence of interspecific hybrids in contact areas between these species. Hybrids are characterized by clear intermediate morphological characteristics, which have taxonomical value, and genetic structure compared to both parental species. We studied mechanisms implicated in drought stress tolerance in seedlings of P. chilensis, P. flexuosa and their interspecific hybrids trying to elucidate if hybrids have a morpho-physiological, growth and survival intermediate response to drought compared to differential parental responses or if they out-perform both parental species when subjected to drought. Our results suggest that hybridization does not result in individuals with intermediate mechanisms related to drought resistance, but with a unique trait combination leading to high growth when water availability is high (similar to the most vulnerable parental species) and high survival under drought stress (similar to the more resistant parental species). Certain uncoupling between symplastic and apoplastic resistence to drought was observed in hybrids, as well as decreased physiological-wood anatomical plasticity compared to parental species. The long-term consequences in terms of adaptive response to drought of this particular trait combination of hybrids remain still unknown.     

Oxidative stress,antioxidants and stress tolerance

Traditionally, reactive oxygen intermediates (ROIs) were considered to be toxic by-products of aerobic metabolism, which were disposed of using antioxidants. However, in recent years, it has become apparent that plants actively produce ROIs as signaling molecules to control processes such as programmed cell death, abiotic stress responses, pathogen defense and systemic signaling. Recent advances including microarray studies and the development of mutants with altered ROI-scavenging mechanisms provide new insights into how the steady-state level of ROIs are controlled in cells. In addition, key steps of the signal transduction pathway that senses ROIs in plants have been identified. These raise several intriguing questions about the relationships between ROI signaling, ROI stress and the production and scavenging of ROIs in the different cellular compartments.     

Revised ranges of seagrass species in the Myeik Archipelago, Myanmar

In a survey of the Myeik Archipelago, we documented seven seagrass species in the southern region. Three seagrass species (Cymodocea rotundata, Enhalus acoroides, and Halophila ovalis) have previously been reported in the Myeik Archipelago; three species (Halodule pinifolia, Halodule uninervis, Syringodium isoetifolium) are new reports for the archipelago; and one species (Thalassia hemprichii) is a new report for Myanmar.     

Contribution of dps to acid stress tolerance and oxidative stress tolerance in Escherichia coli O157:H7

An Escherichia coli O157:H7 dps::nptI mutant (FRIK 47991) was generated, and its survival was compared to that of the parent in HCl (synthetic gastric fluid, pH 1.8) and hydrogen peroxide (15 mM) challenges. The survival of the mutant in log phase (5-h culture) was significantly impaired (4-log(10)-CFU/ml reduction) compared to that of the parent strain (ca. 1.0-log(10)-CFU/ml reduction) after a standard 3-h acid challenge. Early-stationary-phase cells (12-h culture) of the mutant decreased by ca. 4 log(10) CFU/ml while the parent strain decreased by approximately 2 log(10) CFU/ml. No significant differences in the survival of late-stationary-phase cells (24-h culture) between the parent strain and the mutant were observed, although numbers of the parent strain declined less in the initial 1 h of acid challenge. FRIK 47991 was more sensitive to hydrogen peroxide challenge than was the parent strain, although survival improved in stationary phase. Complementation of the mutant with a functional dps gene restored acid and hydrogen peroxide tolerance to levels equal to or greater than those exhibited by the parent strain. These results demonstrate that decreases in survival were from the absence of Dps or a protein regulated by Dps. The results from this study establish that Dps contributes to acid tolerance in E. coli O157:H7 and confirm the importance of Dps in oxidative stress protection.     

An alginate-derived oligosaccharide enhanced wheat tolerance to cadmium stress

Hydroponic experiments were carried out to study the role of alginate-derived oligosaccharides (ADO) in enhancing wheat (Triticum aestivum L.) tolerance to cadmium stress. Data were collected on plant biomass, chlorophyll content, photosynthetic rate, antioxidant enzyme activity and malondialdehyde (MDA) content. Under 100 μM Cd stress, plant growth was significantly inhibited. Shoot length, root length, fresh and dry weight were sharply reduced by 24.21, 34.59, 22.1 and 14.7%, respectively of the control after 10 day of Cd exposure. Superoxide dismutase (SOD), catalase (CAT) and peroxidase (POD) activities were increased and MDA content increased. Wheat seeds were soaked for 5 h in 1,000 mg L⁻¹ ADO solution before cadmium stress. ADO pretreatment alleviated cadmium toxicity symptoms, which were reflected by increasing root and shoot lengths, fresh and dry weight, chlorophyll content and photosynthetic rate (P _n ). Furthermore, ADO pretreatment significantly increased antioxidant enzyme (SOD, CAT and POD) activities and reduced MDA content in leaves and roots. The results indicated that ADO pretreatment partially protected the seedlings from cadmium toxicity during the following growth period.     

Evolution and mechanisms of plant tolerance to flooding stress

Background

In recognition of the 200th anniversary of Charles Darwin''s birth, this short article on flooding stress acknowledges not only Darwin''s great contribution to the concept of evolution but also to the study of plant physiology. In modern biology, Darwin-inspired reductionist physiology continues to shed light on mechanisms that confer competitive advantage in many varied and challenging environments, including those where flooding is prevalent.

Scope

Mild flooding is experienced by most land plants but as its severity increases, fewer species are able to grow and survive. At the extreme, a highly exclusive aquatic lifestyle appears to have evolved numerous times over the past 120 million years. Although only 1–2% of angiosperms are aquatics, some of their adaptive characteristics are also seen in those adopting an amphibious lifestyle where flooding is less frequent. Lowland rice, the staple cereal for much of tropical Asia falls into this category. But, even amongst dry-land dwellers, or certain of their sub-populations, modest tolerance to occasional flooding is to be found, for example in wheat. The collection of papers summarized in this article describes advances to the understanding of mechanisms that explain flooding tolerance in aquatic, amphibious and dry-land plants. Work to develop more tolerant crops or manage flood-prone environments more effectively is also included. The experimental approaches range from molecular analyses, through biochemistry and metabolomics to whole-plant physiology, plant breeding and ecology.Key words: Abiotic stress, adaptation, anoxia, Charles Darwin, environmental stress, evolution, flooding, hypoxia, rice, submergence, wetlands     

Multi-scale spatial patterns of three seagrass species with different growth dynamics

Knowledge of landscape spatial patterns of seagrasses and their rates of loss and natural colonization is critical for understanding the ecology of this group of submerged aquatic plants. Seagrasses form extensive meadows that occupy sheltered coastal seas of the world. In this paper, we examine the multi-scale variability of three seagrass species over a large near-shore region (42 km²) in Western Australia. Geostatistical non-parametric methods were used to explore spatial variation in presence of Amphibolis griffithii , Posidonia coriacea and P. sinuosa , and to identify the spatial scales at which distinct patterns in the species distributions occur: <50, 50–610 and >610 m. Each species showed unique variance structure across local (<50 and 50–610 m) and regional scales (>610 m), suggesting differences in species biology, environmental requirements, inter-species interactions, and their ability to modify their environment. These observations reflect that 1) seagrass landscapes are created by processes that independently act on each seagrass species at different spatial scales; 2) the species' distributions differ in their hydrodynamic forcing, and; 3) seagrass species distributions reflect colonization history such that related species are separated in space because they have different places in the successional sequence. This cross-scale study demonstrates that shoot studies only partly address the spatial structure of seagrass landscapes and further large-scale spatially-explicit research is required before we can interpret the driving processes.