Lolium multiflorum density responses under ozone and herbicide stress

Adaptations to overcrowding of individual plants result in density dependant control of growth and development. There is little information on how anthropogenic stresses modify these responses. We investigated whether combinations of diclofop‐methyl herbicide and tropospheric ozone alter the pattern of expected growth compensation with density changes resulting from intraspecific competition in Lolium multiforum Lam (Poacea) plants. Individual plant vegetative parameters and total seed production were assessed for plants growing under various densities and different herbicide rates and ozone treatments. The stressors differently changed the frequency distribution for average individual plant weight resulting from increasing densities. Only herbicide affected seedling mortality. Plants were able to compensate during grain filling maintaining similar seed production – density relationships in all treatments. Our findings contribute to the understanding of the impact of stress factors on the demographic changes in plant populations. Important ecological implications arise: (i) contrasting responses to ozone and herbicide, alone and in combination of individual plants resulted in different biomass – density relationships; (ii) stress effects on plant populations could not be predicted from individual responses; and (iii) changes in competitive outcome by single or combined stress factors may alter the expected genotype frequency in a crowded population with few dominant individuals.     

The efficient physiological strategy of a novel tomato genotype to adapt to chronic combined water and heat stress

• Climate change is increasing the frequency of high temperature shocks and water shortages, pointing to the need to develop novel tolerant varieties and to understand the mechanisms employed to withstand combined abiotic stresses.
• Two tomato genotypes, a heat-tolerant Solanum lycopersicum accession (LA3120) and a novel genotype (E42), previously selected as a stable yielding genotype under high temperatures, were exposed to single and combined water and heat stress. Plant functional traits, pollen viability and physiological (leaf gas exchange and chlorophyll a fluorescence emission measurements) and biochemical (antioxidant content and antioxidant enzyme activity) measurements were carried out. A Reduced Representation Sequencing approach allowed exploration of the genetic variability of both genotypes to identify candidate genes that could regulate stress responses.
• Both abiotic stresses had a severe impact on plant growth parameters and on the reproductive phase of development. Growth parameters and leaf gas exchange measurements revealed that the two genotypes used different physiological strategies to overcome individual and combined stresses, with E42 having a more efficient capacity to utilize the limiting water resources. Activation of antioxidant defence mechanisms seemed to be critical for both genotypes to counteract combined abiotic stresses. Candidate genes were identified that could explain the different physiological responses to stress observed in E42 compared with LA3120.
• Results here obtained have shown how new tomato genetic resources can be a valuable source of traits for adaptation to combined abiotic stresses and should be used in breeding programmes to improve stress tolerance in commercial varieties.

     

Genetic mapping of the early responses to salt stress in Arabidopsis thaliana

Salt stress decreases plant growth prior to significant ion accumulation in the shoot. However, the processes underlying this rapid reduction in growth are still unknown. To understand the changes in salt stress responses through time and at multiple physiological levels, examining different plant processes within a single set-up is required. Recent advances in phenotyping has allowed the image-based estimation of plant growth, morphology, colour and photosynthetic activity. In this study, we examined the salt stress-induced responses of 191 Arabidopsis accessions from 1 h to 7 days after treatment using high-throughput phenotyping. Multivariate analyses and machine learning algorithms identified that quantum yield measured in the light-adapted state (F_v′/F_m′) greatly affected growth maintenance in the early phase of salt stress, whereas the maximum quantum yield (QY_max) was crucial at a later stage. In addition, our genome-wide association study (GWAS) identified 770 loci that were specific to salt stress, in which two loci associated with QY_max and F_v′/F_m′ were selected for validation using T-DNA insertion lines. We characterized an unknown protein kinase found in the QY_max locus that reduced photosynthetic efficiency and growth maintenance under salt stress. Understanding the molecular context of the candidate genes identified will provide valuable insights into the early plant responses to salt stress. Furthermore, our work incorporates high-throughput phenotyping, multivariate analyses and GWAS, uncovering details of temporal stress responses and identifying associations across different traits and time points, which are likely to constitute the genetic components of salinity tolerance.     

Elucidation of Cross-Talk and Specificity of Early Response Mechanisms to Salt and PEG-Simulated Drought Stresses in Brassica napus Using Comparative Proteomic Analysis

To understand the cross-talk and specificity of the early responses of plants to salt and drought, we performed physiological and proteome analyses of Brassica napus seedlings pretreated with 245 mM NaCl or 25% polyethylene glycol (PEG) 6000 under identical osmotic pressure (-1.0 MPa). Significant decreases in water content and photosynthetic rate and excessive accumulation of compatible osmolytes and oxidative damage were observed in response to both stresses. Unexpectedly, the drought response was more severe than the salt response. We further identified 45 common differentially expressed proteins (DEPs), 143 salt-specific DEPs and 160 drought-specific DEPs by isobaric tags for relative and absolute quantitation (iTRAQ) analysis. The proteome quantitative data were then confirmed by multiple reaction monitoring (MRM). The differences in the proteomic profiles between drought-treated and salt-treated seedlings exceeded the similarities in the early stress responses. Signal perception and transduction, transport and membrane trafficking, and photosynthesis-related proteins were enriched as part of the molecular cross-talk and specificity mechanism in the early responses to the two abiotic stresses. The Ca²⁺ signaling, G protein-related signaling, 14-3-3 signaling pathway and phosphorylation cascades were the common signal transduction pathways shared by both salt and drought stress responses; however, the proteins with executive functions varied. These results indicate functional specialization of family proteins in response to different stresses, i.e., CDPK21, TPR, and CTR1 specific to phosphorylation cascades under early salt stress, whereas STN7 and BSL were specific to phosphorylation cascades under early drought stress. Only the calcium-binding EF-hand family protein and ZKT were clearly identified as signaling proteins that acted as cross-talk nodes for salt and drought signaling pathways. Our study provides new clues and insights for developing strategies to improve the tolerance of crops to complex, multiple environmental stresses.     

Dietary choices are influenced by genotype,mating status,and sex in Drosophila melanogaster

Mating causes many changes in physiology, behavior, and gene expression in a wide range of organisms. These changes are predicted to be sex specific, influenced by the divergent reproductive roles of the sexes. In female insects, mating is associated with an increase in egg production which requires high levels of nutritional input with direct consequences for the physiological needs of individual females. Consequently, females alter their nutritional acquisition in line with the physiological demands imposed by mating. Although much is known about the female mating‐induced nutritional response, far less is known about changes in males. In addition, it is unknown whether variation between genotypes translates into variation in dietary behavioral responses. Here we examine mating‐induced shifts in male and female dietary preferences across genotypes of Drosophila melanogaster. We find sex‐ and genotype‐specific effects on both the quantity and quality of the chosen diet. These results contribute to our understanding of sex‐specific metabolism and reveal genotypic variation that influences responses to physiological demands.     

Cytosolic calcium and pH signaling in plants under salinity stress

Calcium is one of the essential nutrients for growth and development of plants. It is an important component of various structures in cell wall and membranes. Besides some fundamental roles under normal condition, calcium functions as a major secondary-messenger molecule in plants under different developmental cues and various stress conditions including salinity stress. Also changes in cytosolic pH, pH_cyt, either individually, or in coordination with changes in cytosolic Ca²⁺ concentration, [Ca²⁺]_cyt, evoke a wide range of cellular functions in plants including signal transduction in plant-defense responses against stresses. It is believed that salinity stress, like other stresses, is perceived at cell membrane, either extra cellular or intracellular, which then triggers an intracellular-signaling cascade including the generation of secondary messenger molecules like Ca²⁺ and protons. The variety and complexity of Ca²⁺ and pH signaling result from the nature of the stresses as well as the tolerance level of the plant species against that specific stress. The nature of changes in [Ca²⁺]_cyt concentration, in terms of amplitude, frequency and duration, is likely very important for decoding the specific downstream responses for salinity stress tolerance in planta. It has been observed that the signatures of [Ca²⁺]_cyt and pH differ in various studies reported so far depending on the techniques used to measure them, and also depending on the plant organs where they are measured, such as root, shoot tissues or cells. This review describes the recent advances about the changes in [Ca²⁺]_cyt and pH_cyt at both cellular and whole-plant levels under salinity stress condition, and in various salinity-tolerant and -sensitive plant species.Key words: cytosolic calcium, ionic toxicity, osmotic stress, pH, salinity stress, salt tolerance, signaling     

Changes in the chlorophyll content of grape leaves could provide a physiological index for responses and adaptation to UV‐C radiation

Stilbenes are a group of phytoalexins that play an important role in grapevine (Vitis) basal immunity and can be induced by biotic and abiotic stresses. The levels of chlorophylls, the main pigments in plant cells, can also indicate the tolerance of plants to various stresses. Here, the response of different grapevine genotypes to UV‐C radiation treatment was tested and the abundance of chlorophyll in the Hoe29 and Ke53 genotypes was observed to increase significantly within 6 h of UV‐C treatment. Conversely, chlorophyll levels decreased markedly in the Augster Weiss and Müller–Thurgau genotypes. Furthermore, stilbene abundance increased substantially in the Hoe29, Ke53, Ke83 and Pinot Blanc genotypes, but increased only slightly in Augster Weiss and Müller–Thurgau. The expression of resveratrol synthase, which encodes a key enzyme in the stilbene synthesis pathway, increased in Hoe29, Ke53, Ke83 and Pinot Blanc following UV‐C treatment, in a manner consistent with stilbene accumulation. In addition, we observed that reactive oxygen species (ROS) provide a key trigger in physiological responses and changes in secondary metabolite contents. In summary, the results from this study support a link between ROS, chlorophyll levels and genetic diversity for stilbene abundance in different grape genotypes, providing insights into mechanisms for plant physiological and biochemical responses and adaptations to stress.     

Multifaceted roles of aquaporins as molecular conduits in plant responses to abiotic stresses

Abiotic stress has become a challenge to food security due to occurrences of climate change and environmental degradation. Plants initiate molecular, cellular and physiological changes to respond and adapt to various types of abiotic stress. Understanding of plant response mechanisms will aid in strategies aimed at improving stress tolerance in crop plants. One of the most common and early symptoms associated with these stresses is the disturbance in plant–water homeostasis, which is regulated by a group of proteins called “aquaporins”. Aquaporins constitute a small family of proteins which are classified further on the basis of their localization, such as plasma membrane intrinsic proteins, tonoplast intrinsic proteins, nodulin26-like intrinsic proteins (initially identified in symbiosomes of legumes but also found in the plasma membrane and endoplasmic reticulum), small basic intrinsic proteins localized in ER (endoplasmic reticulum) and X intrinsic proteins present in plasma membrane. Apart from water, aquaporins are also known to transport CO₂, H₂O₂, urea, ammonia, silicic acid, arsenite and wide range of small uncharged solutes. Besides, aquaporins also function to modulate abiotic stress-induced signaling. Such kind of versatile functions has made aquaporins a suitable candidate for development of transgenic plants with increased tolerance toward different abiotic stress. Toward this endeavor, the present review describes the versatile functions of aquaporins in water uptake, nutrient balancing, long-distance signal transfer, nutrient/heavy metal acquisition and seed development. Various functional genomic studies showing the potential of specific aquaporin isoforms for enhancing plant abiotic stress tolerance are summarized and future research directions are given to design stress-tolerant crops.     

Genetic analysis of involvement of ETR1 in plant response to salt and osmotic stress

The involvement of ethylene and ethylene receptor Ethylene Response 1 (ETR1) in plant stress responses has been highlighted. However, the physiological processes involved remain unclear. In this study, we have investigated the physiological response of two alleles etr1-1 and etr1-7 mutants during germination and post-germination seedling development in response to salt and osmotic stress. The etr1-1 mutants showed increased sensitivity to osmotic (200 mM or higher mannitol) and salt stress (50 mM NaCl or higher) during germination and seedling development, whereas the etr1-7 mutants displayed enhanced tolerance to the severe stresses (500 mM mannitol or 200 mM NaCl). These results provide physiological and genetic evidence that ethylene receptor ETR1 modulates plant response to abiotic stress. Furthermore, the etr1-1 and etr1-7 mutants showed different responses to exogenous abscisic acid (ABA) inhibition. The etr1-1 mutants were more sensitive to ABA than the wild type during germination, and young seedling development. In sharp contrast, the etr1-7 mutants showed enhanced insensitivity to ABA treatment (>1 μM ABA) in post-germination development including root elongation and greening of cotyledons of the treated seedlings, although the germination was not greatly altered at the tested doses of ABA. The results suggest that ETR1-modulated stress response may mediate ABA. Youning Wang and Tao Wang contributed equally to this report.