Global warming enhances sulphide stress in a key seagrass species (NW Mediterranean)

The build‐up of sulphide concentrations in sediments, resulting from high inputs of organic matter and the mineralization through sulphate reduction, can be lethal to the benthos. Sulphate reduction is temperature dependent, thus global warming may contribute to even higher sulphide concentrations and benthos mortality. The seagrass Posidonia oceanica is very sensitive to sulphide stress. Hence, if concentrations build up with global warming, this key Mediterranean species could be seriously endangered. An 8‐year monitoring of daily seawater temperature, the sulphur isotopic signatures of water (δ³⁴S_water), sediment (δ³⁴S_CRS) and P. oceanica leaf tissue (δ³⁴S_leaves), along with total sulphur in leaves (TS_leaves) and annual net population growth along the coast of the Balearic archipelago (Western Mediterranean) allowed us to determine if warming triggers P. oceanica sulphide stress and constrains seagrass survival. From the isotopic S signatures, we estimated sulphide intrusion into the leaves (F_sulphide) and sulphur incorporation into the leaves from sedimentary sulphides (SS_leaves). We observed lower δ³⁴S_leaves, higher F_sulphide and SS_leaves coinciding with a 6‐year period when two heat waves were recorded. Warming triggered sulphide stress as evidenced by the negative temperature dependence of δ³⁴S_leaves and the positive one of F_sulphide, TS_leaves and SS_leaves. Lower P. oceanica net population growth rates were directly related to higher contents of TS_leaves. At equivalent annual maximum sea surface water temperature (SST_max), deep meadows were less affected by sulphide intrusion than shallow ones. Thus, water depth acts as a protecting mechanism against sulphide intrusion. However, water depth would be insufficient to buffer seagrass sulphide stress triggered by Mediterranean seawater summer temperatures projected for the end of the 21st century even under scenarios of moderate greenhouse gas emissions, A1B. Mediterranean warming, therefore, is expected to enhance P. oceanica sulphide stress, and thus compromise the survival of this key habitat along its entire depth distribution range.     

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.     

盐胁迫下树种幼苗生长及其耐盐性

采用盆栽方法,以11个树种实生幼苗为材料,用不同浓度(0、3、5、8 g·kg-1和10 g·kg-1)NaCl溶液进行1次性浇灌处理,对盐胁迫下各树种的形态表现、生长及耐盐性进行了研究,结果表明:(1)当盐含量达到8 g·kg-1时,欧洲荚蒾、甜桦和光叶漆植株死亡,当含量增加到10 g·kg-1时,沃氏金链花植株死亡,其它各存活树种也均出现不同程度的盐害症状;(2)盐胁迫后,各树种的苗高生长量下降、生物量累积减少,且随着处理浓度的增加均呈下降趋势,其中榆桔、甜桦和光叶漆的降幅最大;(3)盐处理后,各树种的根冠比值增大,其中盐胁迫对光叶漆、银水牛果和沃氏金链花有显著影响(p<0.05);(4)综合分析各树种的生长和形态表现,认为日本丁香、银水牛果、三裂叶漆和豆梨具有高度耐盐性,沃氏金链花、金雀儿、鹰爪豆和榆桔具有中高度耐盐性,而欧洲荚蒾、甜桦和光叶漆具有中度耐盐性.     

Genomic approaches to plant stress tolerance

Past efforts to improve plant tolerance to drought, high salinity and low-temperature through breeding and genetic engineering have had limited success owing to the genetic complexity of stress responses. Progress is now anticipated through comparative genomics studies of an evolutionarily diverse set of model organisms, and through the use of techniques such as high-throughput analysis of expressed sequence tags, large-scale parallel analysis of gene expression, targeted or random mutagenesis, and gain-of-function or mutant complementation. The discovery of novel genes, determination of their expression patterns in response to abiotic stress, and an improved understanding of their roles in stress adaptation (obtained by the use of functional genomics) will provide the basis of effective engineering strategies leading to greater stress tolerance.     

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 ...     

Thresholds for morphological response to light reduction for four tropical seagrass species

Seagrasses worldwide are highly vulnerable to, and at increasing risk from reduced light availability, and robust light thresholds are required for evaluating future impacts of changing light conditions. We tested the morphological response (shoot density and growth) of four Indo-West Pacific seagrass species (Cymodocea serrulata, Halodule uninervis, Halophila ovalis and Zostera muelleri) to six daily light levels ranging from 0 to 23 mol m⁻² d⁻¹ (0–70% surface irradiance) in cool (∼23 °C) and warm temperatures (∼28 °C) over 14 weeks. The impact of light limitation on shoot densities and growth rates was higher at warm than at cool temperatures, and for Z. muelleri and H. ovalis than for C. serrulata and H. uninervis, in terms of both the time taken for the low light treatment to take effect and the predicted time to shoot loss (e.g. 17–143 days at 0 mol m⁻² d⁻¹). Using fitted curves we estimated temperature-dependent thresholds (with estimates of uncertainty) for 50% and 80% protection of growth and shoot density, defined here as “potential light thresholds” in recognition that they were derived under experimental conditions. Potential light thresholds that maintained 50% and 80% of seagrass shoot density fell within the ranges 1.1–5.7 mol m⁻² d⁻¹ and 3.8–10.4 mol m⁻² d⁻¹, respectively, depending on temperature and species. Light thresholds calculated in separate in situ studies for two of the same species produced comparable results. We propose that the upper (rounded) values of 6 mol m⁻² d⁻¹ and 10 mol m⁻² d⁻¹ can be used as potential light thresholds for protecting 50% and 80% of shoot density for these four species over 14 weeks. As management guidelines should always be more conservative than thresholds for biological declines, we used error estimates to provide a quantitative method for converting potential light thresholds into guidelines that satisfy this criterion. The present study demonstrates a new approach to deriving potential light thresholds for acute impacts, describes how they can be applied in management guidelines and quantifies the timescales of seagrass decline in response to light limitation. This method can be used to further quantify cumulative impacts on potential light thresholds.     

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.     

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.     

高温胁迫下五种杜鹃花属植物的生理变化及其耐热性比较

高温是制约分布于较高海拔地区杜鹃花迁地保育与园林应用的重要因子.为探讨杜鹃花属植物的 高温致伤机理,该实验以隶属不同亚属的白花杜鹃、羊踯躅、毛棉杜鹃、红滩杜鹃及红棕杜鹃4年生实生苗为 材料,通过人工气候箱的盆栽实验,研究了30℃、38℃高温胁迫下其叶片生理生化指标的变化,并利用隶属 函数法及系统聚类分析法对其种间...     

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.     

Approaches to improve stress tolerance using molecular genetics

Plant productivity is greatly affected by environmental stress factors. In this review, we give an overview of molecular approaches that have been taken to study stress tolerance; in particular, we consider drought, salt and cold stress. Strategies and perspectives in using molecular biology to improve stress tolerance are outlined describing specific examples. Osmotic stress is associated with the synthesis of novel polypeptides and/or osmolytes. The spectrum and action of these different metabolites are summarized. A number of stress-related genes have been characterized and several representatives are discussed. After transforming plants with these genes, the effect of the encoded proteins on altered stress behaviour is examined. If genes with enzymatic functions were chosen for these experiments, complete pathways may be altered and this can implement the production of novel metabolites conferring stress tolerance.