Role and Functional Differences of HKT1-Type Transporters in Plants under Salt Stress.

Abiotic stresses generally cause a series of morphological, biochemical and molecular changes that unfavorably affect plant growth and productivity. Among these stresses, soil salinity is a major threat that can seriously impair crop yield. To cope with the effects of high salinity on plants, it is important to understand the mechanisms that plants use to deal with it, including those activated in response to disturbed Na⁺ and K⁺ homeostasis at cellular and molecular levels. HKT1-type transporters are key determinants of Na⁺ and K⁺ homeostasis under salt stress and they contribute to reduce Na⁺-specific toxicity in plants. In this review, we provide a brief overview of the function of HKT1-type transporters and their importance in different plant species under salt stress. Comparison between HKT1 homologs in different plant species will shed light on different approaches plants may use to cope with salinity.

Root inoculation with Azotobacter chroococcum 76A enhances tomato plants adaptation to salt stress under low N conditions.

BACKGROUND: The emerging roles of rhizobacteria in improving plant nutrition and stress protection have great potential for sustainable use in saline soils. We evaluated the function of the salt-tolerant strain Azotobacter chroococcum 76A as stress protectant in an important horticultural crop, tomato. Specifically we hypothesized that treatment of tomato plants with A. chroococcum 76A could improve plant performance under salinity stress and sub-optimal nutrient regimen. RESULTS: Inoculation of Micro Tom tomato plants with A. chroococcum 76A increased numerous growth parameters and also conferred protective effects under both moderate (50 mM NaCl) and severe (100 mM NaCl) salt stresses. These benefits were mostly observed under reduced nutrient regimen and were less appreciable in optimal nitrogen conditions. Therefore, the efficiency of A. chroococcum 76A was found to be dependent on the nutrient status of the rhizosphere. The expression profiles of LEA genes indicated that A. chroococcum 76A treated plants were more responsive to stress stimuli when compared to untreated controls. However, transcript levels of key nitrogen assimilation genes revealed that the optimal nitrogen regimen, in combination with the strain A. chroococcum 76A, may have saturated plant's ability to assimilate nitrogen. CONCLUSIONS: Roots inoculation with A. chroococcum 76A tomato promoted tomato plant growth, stress tolerance and nutrient assimilation efficiency under moderate and severe salinity. Inoculation with beneficial bacteria such as A. chroococcum 76A may be an ideal solution for low-input systems, where environmental constraints and limited chemical fertilization may affect the potential yield.

It's Hard to Avoid Avoidance: Uncoupling the Evolutionary Connection between Plant Growth, Productivity and Stress "Tolerance".

In the last 100 years, agricultural developments have favoured selection for highly productive crops, a fact that has been commonly associated with loss of key traits for environmental stress tolerance. We argue here that this is not exactly the case. We reason that high yield under near optimal environments came along with hypersensitization of plant stress perception and consequently early activation of stress avoidance mechanisms, such as slow growth, which were originally needed for survival over long evolutionary time periods. Therefore, mechanisms employed by plants to cope with a stressful environment during evolution were overwhelmingly geared to avoid detrimental effects so as to ensure survival and that plant stress "tolerance" is fundamentally and evolutionarily based on "avoidance" of injury and death which may be referred to as evolutionary avoidance (EVOL-Avoidance). As a consequence, slow growth results from being exposed to stress because genes and genetic programs to adjust growth rates to external circumstances have evolved as a survival but not productivity strategy that has allowed extant plants to avoid extinction. To improve productivity under moderate stressful conditions, the evolution-oriented plant stress response circuits must be changed from a survival mode to a continued productivity mode or to avoid the evolutionary avoidance response, as it were. This may be referred to as Agricultural (AGRI-Avoidance). Clearly, highly productive crops have kept the slow, reduced growth response to stress that they evolved to ensure survival. Breeding programs and genetic engineering have not succeeded to genetically remove these responses because they are polygenic and redundantly programmed. From the beginning of modern plant breeding, we have not fully appreciated that our crop plants react overly-cautiously to stress conditions. They over-reduce growth to be able to survive stresses for a period of time much longer than a cropping season. If we are able to remove this polygenic redundant survival safety net we may improve yield in moderately stressful environments, yet we will face the requirement to replace it with either an emergency slow or no growth (dormancy) response to extreme stress or use resource management to rescue crops under extreme stress (or both).

A Single Amino-Acid Substitution in the Sodium Transporter HKT1 Associated with Plant Salt Tolerance.

A crucial prerequisite for plant growth and survival is the maintenance of potassium uptake, especially when high sodium surrounds the root zone. The Arabidopsis HIGH-AFFINITY K(+) TRANSPORTER1 (HKT1), and its homologs in other salt-sensitive dicots, contributes to salinity tolerance by removing Na(+) from the transpiration stream. However, TsHKT1;2, one of three HKT1 copies in Thellungiella salsuginea, a halophytic Arabidopsis relative, acts as a K(+) transporter in the presence of Na(+) in yeast (Saccharomyces cerevisiae). Amino-acid sequence comparisons indicated differences between TsHKT1;2 and most other published HKT1 sequences with respect to an Asp residue (D207) in the second pore-loop domain. Two additional T salsuginea and most other HKT1 sequences contain Asn (n) in this position. Wild-type TsHKT1;2 and altered AtHKT1 (AtHKT1(N-D)) complemented K(+)-uptake deficiency of yeast cells. Mutant hkt1-1 plants complemented with both AtHKT1(N) (-) (D) and TsHKT1;2 showed higher tolerance to salt stress than lines complemented by the wild-type AtHKT1 Electrophysiological analysis in Xenopus laevis oocytes confirmed the functional properties of these transporters and the differential selectivity for Na(+) and K(+) based on the n/d variance in the pore region. This change also dictated inward-rectification for Na(+) transport. Thus, the introduction of Asp, replacing Asn, in HKT1-type transporters established altered cation selectivity and uptake dynamics. We describe one way, based on a single change in a crucial protein that enabled some crucifer species to acquire improved salt tolerance, which over evolutionary time may have resulted in further changes that ultimately facilitated colonization of saline habitats.

Morpho-physiological adaptations to weed competition impair green bean (Phaseolus vulgaris) ability to overcome moderate salt stress.

The two stresses of weed competition and salt salinity lead to crop yield losses and decline in the productivity of agricultural land. These constraints threaten the future of food production because weeds are more salt stress tolerant than most crops. Climate change will lead to an increase of soil salinity worldwide, and possibly exacerbate the competition between weeds and crops. This aspect has been scarcely investigated in the context of weed-crop competition. Therefore, we conducted a field experiment on green beans (Phaseolus vulgaris ) to investigate the combined impact of weed competition and salt stress on key morpho-physiological traits, and crop yield. We demonstrated that soil salinity shifted weed composition toward salt tolerant weed species (Portulaca oleracea and Cynodon dactylon ), while it reduced the presence of lower tolerance species. Weed competition activated adaptation responses in green bean such as reduced leaf mass per area and biomass allocation to the stem, unchanged stomatal density and instantaneous water use efficiency, which diverge from those that are typically observed as a consequence of salt stress. The morpho-physiological modifications caused by weeds is attributed to the alterations of light intensity and/or quality, further confirming the pivotal role of the light in crop response to weeds. We concluded that higher yield loss caused by combined salt stress and weed competition is due to impaired morpho-physiological responses, which highlights the negative interaction between salt stress and weed competition. This phenomenon will likely be more frequent in the future, and potentially reduce the efficacy of current weed control methods.

RafanoSet: Dataset of raw, manually, and automatically annotated Raphanus Raphanistrum weed images for object detection and segmentation.

The rationale for this data article is to provide resources which could facilitate the studies focussed over weed detection and segmentation in precision farming using computer vision. We have curated Multispectral (MS) images over crop fields of Triticum Aestivum containing heterogenous mix of Raphanus raphanistrum in both uniform and random crop spacing. This dataset is designed to facilitate weed detection and segmentation based on manual and automatically annotated Raphanus raphanistrum, commonly known as wild radish. The dataset is publicly available through the Zenodo data library and provides annotated pixel-level information that is crucial for registration and segmentation purposes. The dataset consists of 85 original MS images captured over 17 scenes covering various spectra including Blue, Green, Red, NIR (Near-Infrared), and RedEdge. Each image has a dimension of 1280 × 960 pixels and serves as the basis for the specific weed detection and segmentation. Manual annotations were performed using Visual Geometry Group Image Annotator (VIA) and the results were saved in Common Objects in Context (COCO) segmentation format. To facilitate this resource-intensive task of annotation, a Grounding DINO + Segment Anything Model (SAM) was trained with this manually annotated data to obtain automated Visual Object Classes Extended Markup Language (PASCAL VOC) annotations for 80 MS images. The dataset emphasizes quality control, validating both the 'manual" and 'automated" repositories by extracting and evaluating binary masks. The codes used for these processes are accessible to ensure transparency and reproducibility. This dataset is the first-of-its-kind public resource providing manual and automatically annotated weed information over close-ranged MS images in heterogenous agriculture environment. Researchers and practitioners in the fields of precision agriculture and computer vision can use this dataset to improve MS image registration and segmentation at close range photogrammetry with a focus on wild radish. The dataset not only helps with intra-subject registration to improve segmentation accuracy, but also provides valuable spectral information for training and refining machine learning models.

Comprehensive Evaluation of Multispectral Image Registration Strategies in Heterogenous Agriculture Environment.

This article is focused on the comprehensive evaluation of alleyways to scale-invariant feature transform (SIFT) and random sample consensus (RANSAC) based multispectral (MS) image registration. In this paper, the idea is to extensively evaluate three such SIFT- and RANSAC-based registration approaches over a heterogenous mix containing Triticum aestivum crop and Raphanus raphanistrum weed. The first method is based on the application of a homography matrix, derived during the registration of MS images on spatial coordinates of individual annotations to achieve spatial realignment. The second method is based on the registration of binary masks derived from the ground truth of individual spectral channels. The third method is based on the registration of only the masked pixels of interest across the respective spectral channels. It was found that the MS image registration technique based on the registration of binary masks derived from the manually segmented images exhibited the highest accuracy, followed by the technique involving registration of masked pixels, and lastly, registration based on the spatial realignment of annotations. Among automatically segmented images, the technique based on the registration of automatically predicted mask instances exhibited higher accuracy than the technique based on the registration of masked pixels. In the ground truth images, the annotations performed through the near-infrared channel were found to have a higher accuracy, followed by green, blue, and red spectral channels. Among the automatically segmented images, the accuracy of the blue channel was observed to exhibit a higher accuracy, followed by the green, near-infrared, and red channels. At the individual instance level, the registration based on binary masks depicted the highest accuracy in the green channel, followed by the method based on the registration of masked pixels in the red channel, and lastly, the method based on the spatial realignment of annotations in the green channel. The instance detection of wild radish with YOLOv8l-seg was observed at a mAP@0.5 of 92.11% and a segmentation accuracy of 98% towards segmenting its binary mask instances.

GobhiSet: Dataset of raw, manually, and automatically annotated RGB images across phenology of Brassica oleracea var. Botrytis.

This research introduces an extensive dataset of unprocessed aerial RGB images and orthomosaics of Brassica oleracea crops, captured via a DJI Phantom 4. The dataset, publicly accessible, comprises 244 raw RGB images, acquired over six distinct dates in October and November of 2020 as well as 6 orthomosaics from an experimental farm located in Portici, Italy. The images, uniformly distributed across crop spaces, have undergone both manual and automatic annotations, to facilitate the detection, segmentation, and growth modelling of crops. Manual annotations were performed using bounding boxes via the Visual Geometry Group Image Annotator (VIA) and exported in the Common Objects in Context (COCO) segmentation format. The automated annotations were generated using a framework of Grounding DINO + Segment Anything Model (SAM) facilitated by YOLOv8x-seg pretrained weights obtained after training manually annotated images dated 8 October, 21 October, and 29 October 2020. The automated annotations were archived in Pascal Visual Object Classes (PASCAL VOC) format. Seven classes, designated as Row 1 through Row 7, have been identified for crop labelling. Additional attributes such as individual crop ID and the repetitiveness of individual crop specimens are delineated in the Comma Separated Values (CSV) version of the manual annotation. This dataset not only furnishes annotation information but also assists in the refinement of various machine learning models, thereby contributing significantly to the field of smart agriculture. The transparency and reproducibility of the processes are ensured by making the utilized codes accessible. This research marks a significant stride in leveraging technology for vision-based crop growth monitoring.

Effectiveness of bio-effectors on maize, wheat and tomato performance and phosphorus acquisition from greenhouse to field scales in Europe and Israel: a meta-analysis.

Biostimulants (Bio-effectors, BEs) comprise plant growth-promoting microorganisms and active natural substances that promote plant nutrient-acquisition, stress resilience, growth, crop quality and yield. Unfortunately, the effectiveness of BEs, particularly under field conditions, appears highly variable and poorly quantified. Using random model meta-analyses tools, we summarize the effects of 107 BE treatments on the performance of major crops, mainly conducted within the EU-funded project BIOFECTOR with a focus on phosphorus (P) nutrition, over five years. Our analyses comprised 94 controlled pot and 47 field experiments under different geoclimatic conditions, with variable stress levels across European countries and Israel. The results show an average growth/yield increase by 9.3% (n=945), with substantial differences between crops (tomato > maize > wheat) and growth conditions (controlled nursery + field (Seed germination and nursery under controlled conditions and young plants transplanted to the field) > controlled > field). Average crop growth responses were independent of BE type, P fertilizer type, soil pH and plant-available soil P (water-P, Olsen-P or Calcium acetate lactate-P). BE effectiveness profited from manure and other organic fertilizers, increasing soil pH and presence of abiotic stresses (cold, drought/heat or salinity). Systematic meta-studies based on published literature commonly face the inherent problem of publication bias where the most suspected form is the selective publication of statistically significant results. In this meta-analysis, however, the results obtained from all experiments within the project are included. Therefore, it is free of publication bias. In contrast to reviews of published literature, our unique study design is based on a common standardized protocol which applies to all experiments conducted within the project to reduce sources of variability. Based on data of crop growth, yield and P acquisition, we conclude that application of BEs can save fertilizer resources in the future, but the efficiency of BE application depends on cropping systems and environments.

The Arabidopsis thaliana mutant air1 implicates SOS3 in the regulation of anthocyanins under salt stress.

The accumulation of anthocyanins in plants exposed to salt stress has been largely documented. However, the functional link and regulatory components underlying the biosynthesis of these molecules during exposure to stress are largely unknown. In a screen of second site suppressors of the salt overly sensitive3-1 (sos3-1) mutant, we isolated the anthocyanin-impaired-response-1 (air1) mutant. air1 is unable to accumulate anthocyanins under salt stress, a key phenotype of sos3-1 under high NaCl levels (120 mM). The air1 mutant showed a defect in anthocyanin production in response to salt stress but not to other stresses such as high light, low phosphorous, high temperature or drought stress. This specificity indicated that air1 mutation did not affect anthocyanin biosynthesis but rather its regulation in response to salt stress. Analysis of this mutant revealed a T-DNA insertion at the first exon of an Arabidopsis thaliana gene encoding for a basic region-leucine zipper transcription factor. air1 mutants displayed higher survival rates compared to wild-type in oxidative stress conditions, and presented an altered expression of anthocyanin biosynthetic genes such as F3H, F3'H and LDOX in salt stress conditions. The results presented here indicate that AIR1 is involved in the regulation of various steps of the flavonoid and anthocyanin accumulation pathways and is itself regulated by the salt-stress response signalling machinery. The discovery and characterization of AIR1 opens avenues to dissect the connections between abiotic stress and accumulation of antioxidants in the form of flavonoids and anthocyanins.

Valorisation of hydrothermal liquefaction wastewater in agriculture: effects on tobacco plants and rhizosphere microbiota.

Industrial wastewater obtained from hydrothermal liquefaction (HTL-WW) of food wastes for biofuels production could represent a source of crop nutrients since it is characterized by a high amount of organic and inorganic compounds. In the present work, the potential use of HTL-WW as irrigation water for industrial crops was investigated. The composition of the HTL-WW was rich in nitrogen, phosphorus, and potassium with high level of organic carbon. A pot experiment with Nicotiana tabacum L. plants was conducted using diluted wastewater to reduce the concentration of some chemical elements below the official accepted threshold values. Plants were grown in the greenhouse under controlled conditions for 21 days and irrigated with diluted HTL-WW every 24 hours. Soils and plants were sampled every seven days to evaluate, over time, the effect of wastewater irrigation both on soil microbial populations, through high-throughput sequencing, and plant growth parameters, through the measurement of different biometric indices. Metagenomic results highlighted that, in the HTL-WW treated rhizosphere, the microbial populations shifted via their mechanisms of adaptation to the new environmental conditions, establishing a new balance among bacterial and fungal communities. Identification of microbial taxa occurring in the rhizosphere of tobacco plants during the experiment highlighted that the HTL-WW application improved the growth of Micrococcaceae, Nocardiaceae and Nectriaceae, which included key species for denitrification, organic compounds degradation and plant growth promotion. As a result, irrigation with HTL-WW improved the overall performance of tobacco plants which showed higher leaf greenness and increased number of flowers compared to irrigated control plants. Overall, these results demonstrate the potential feasibility of using of HTL-WW in irrigated agriculture.

Inoculation with a microbial consortium increases soil microbial diversity and improves agronomic traits of tomato under water and nitrogen deficiency.

Microbial-based biostimulants, functioning as biotic and abiotic stress protectants and growth enhancers, are becoming increasingly important in agriculture also in the context of climate change. The search for new products that can help reduce chemical inputs under a variety of field conditions is the new challenge. In this study, we tested whether the combination of two microbial growth enhancers with complementary modes of action, Azotobacter chroococcum 76A and Trichoderma afroharzianum T22, could facilitate tomato adaptation to a 30% reduction of optimal water and nitrogen requirements. The microbial inoculum increased tomato yield (+48.5%) under optimal water and nutrient conditions. In addition, the microbial application improved leaf water potential under stress conditions (+9.5%), decreased the overall leaf temperature (-4.6%), and increased shoot fresh weight (+15%), indicating that this consortium could act as a positive regulator of plant water relations under limited water and nitrogen availability. A significant increase in microbial populations in the rhizosphere with applications of A. chroococcum 76A and T. afroharzianum T22 under stress conditions, suggested that these inoculants could enhance soil microbial abundance, including the abundance of native beneficial microorganisms. Sampling time, limited water and nitrogen regimes and microbial inoculations all affected bacterial and fungal populations in the rhizospheric soil. Overall, these results indicated that the selected microbial consortium could function as plant growth enhancer and stress protectant, possibly by triggering adaptation mechanisms via functional changes in the soil microbial diversity and relative abundance.

Transcriptomic and splicing changes underlying tomato responses to combined water and nutrient stress.

Tomato is a horticultural crop of high economic and nutritional value. Suboptimal environmental conditions, such as limited water and nutrient availability, cause severe yield reductions. Thus, selection of genotypes requiring lower inputs is a goal for the tomato breeding sector. We screened 10 tomato varieties exposed to water deficit, low nitrate or a combination of both. Biometric, physiological and molecular analyses revealed different stress responses among genotypes, identifying T270 as severely affected, and T250 as tolerant to the stresses applied. Investigation of transcriptome changes caused by combined stress in roots and leaves of these two genotypes yielded a low number of differentially expressed genes (DEGs) in T250 compared to T270, suggesting that T250 tailors changes in gene expression to efficiently respond to combined stress. By contrast, the susceptible tomato activated approximately one thousand and two thousand genes in leaves and roots respectively, indicating a more generalized stress response in this genotype. In particular, developmental and stress-related genes were differentially expressed, such as hormone responsive factors and transcription factors. Analysis of differential alternative splicing (DAS) events showed that combined stress greatly affects the splicing landscape in both genotypes, highlighting the important role of AS in stress response mechanisms. In particular, several stress and growth-related genes as well as transcription and splicing factors were differentially spliced in both tissues. Taken together, these results reveal important insights into the transcriptional and post-transcriptional mechanisms regulating tomato adaptation to growth under reduced water and nitrogen inputs.

A Novel Protein Hydrolysate-Based Biostimulant Improves Tomato Performances under Drought Stress.

Abiotic stresses adversely affect crop production causing yield reductions in important crops, including tomato (Solanum lycopersicum L.). Among the different abiotic stresses, drought is considered to be the most critical one, since limited water availability negatively impacts plant growth and development, especially in arid and semi-arid areas. The aim of this study was to understand how biostimulants may interact with critical physiological response mechanisms in tomato under limited water availability and to define strategies to improve tomato performances under drought stress. We investigated the physiological responses of the tomato genotype 'E42' grown in open fields under optimal conditions (100% irrigation) and limited water availability (50% irrigation) treated or not with a novel protein hydrolysate-based biostimulant (CycoFlow, Agriges, BN, Italy). Plants treated with the protein hydrolysate showed a better water status and pollen viability, which also resulted in higher yield under drought stress compared to untreated plants. The treatment with the biostimulant had also an effect on antioxidant contents and activity in leaves and fruits depending on the level of irrigation provided. Altogether, these results indicate that the application of protein hydrolysates on tomato improved plant performances under limited water availability and in different experimental fields.

Anthocyanins are Key Regulators of Drought Stress Tolerance in Tobacco.

Abiotic stresses will be one of the major challenges for worldwide food supply in the near future. Therefore, it is important to understand the physiological mechanisms that mediate plant responses to abiotic stresses. When subjected to UV, salinity or drought stress, plants accumulate specialized metabolites that are often correlated with their ability to cope with the stress. Among them, anthocyanins are the most studied intermediates of the phenylpropanoid pathway. However, their role in plant response to abiotic stresses is still under discussion. To better understand the effects of anthocyanins on plant physiology and morphogenesis, and their implications on drought stress tolerance, we used transgenic tobacco plants (AN1), which over-accumulated anthocyanins in all tissues. AN1 plants showed an altered phenotype in terms of leaf gas exchanges, leaf morphology, anatomy and metabolic profile, which conferred them with a higher drought tolerance compared to the wild-type plants. These results provide important insights for understanding the functional reason for anthocyanin accumulation in plants under stress.

Ascophyllum nodosum Based Extracts Counteract Salinity Stress in Tomato by Remodeling Leaf Nitrogen Metabolism.

Biostimulants have rapidly and widely been adopted as growth enhancers and stress protectants in agriculture, however, due to the complex nature of these products, their mechanism of action is not clearly understood. By using two algal based commercial biostimulants in combination with the Solanum lycopersicum cv. MicroTom model system, we assessed how the modulation of nitrogen metabolites and potassium levels could contribute to mediate physiological mechanisms that are known to occur in response to salt/and or osmotic stress. Here we provide evidence that the reshaping of amino acid metabolism can work as a functional effector, coordinating ion homeostasis, osmotic adjustment and scavenging of reactive oxygen species under increased osmotic stress in MicroTom plant cells. The Superfifty biostimulant is responsible for a minor amino acid rich-phenotype and could represent an interesting instrument to untangle nitrogen metabolism dynamics in response to salinity and/or osmotic stress.

A comparative study of salt tolerance parameters in 11 wild relatives of Arabidopsis thaliana.

Salinity is an abiotic stress that limits both yield and the expansion of agricultural crops to new areas. In the last 20 years our basic understanding of the mechanisms underlying plant tolerance and adaptation to saline environments has greatly improved owing to active development of advanced tools in molecular, genomics, and bioinformatics analyses. However, the full potential of investigative power has not been fully exploited, because the use of halophytes as model systems in plant salt tolerance research is largely neglected. The recent introduction of halophytic Arabidopsis-Relative Model Species (ARMS) has begun to compare and relate several unique genetic resources to the well-developed Arabidopsis model. In a search for candidates to begin to understand, through genetic analyses, the biological bases of salt tolerance, 11 wild relatives of Arabidopsis thaliana were compared: Barbarea verna, Capsella bursa-pastoris, Hirschfeldia incana, Lepidium densiflorum, Malcolmia triloba, Lepidium virginicum, Descurainia pinnata, Sisymbrium officinale, Thellungiella parvula, Thellungiella salsuginea (previously T. halophila), and Thlaspi arvense. Among these species, highly salt-tolerant (L. densiflorum and L. virginicum) and moderately salt-tolerant (M. triloba and H. incana) species were identified. Only T. parvula revealed a true halophytic habitus, comparable to the better studied Thellungiella salsuginea. Major differences in growth, water transport properties, and ion accumulation are observed and discussed to describe the distinctive traits and physiological responses that can now be studied genetically in salt stress research.

Systemin-dependent salinity tolerance in tomato: evidence of specific convergence of abiotic and biotic stress responses.

Plants have evolved complex mechanisms to perceive environmental cues and develop appropriate and coordinated responses to abiotic and biotic stresses. Considerable progress has been made towards a better understanding of the molecular mechanisms of plant response to a single stress. However, the existence of cross-tolerance to different stressors has proved to have great relevance in the control and regulation of organismal adaptation. Evidence for the involvement of the signal peptide systemin and jasmonic acid in wound-induced salt stress adaptation in tomato has been provided. To further unravel the functional link between plant responses to salt stress and mechanical damage, transgenic tomato (Lycopersicon esculentum Mill.) plants constitutively expressing the prosystemin cDNA have been exposed to a moderate salt stress. Prosystemin over-expression caused a reduction in stomatal conductance. However, in response to salt stress, prosystemin transgenic plants maintained a higher stomatal conductance compared with the wild-type control. Leaf concentrations of abscissic acid (ABA) and proline were lower in stressed transgenic plants compared with their wild-type control, implying that either the former perceived a less stressful environment or they adapted more efficiently to it. Consistently, under salt stress, transgenic plants produced a higher biomass, indicating that a constitutive activation of wound responses is advantageous in saline environment. Comparative gene expression profiling of stress-induced genes suggested that the partial stomatal closure was not mediated by ABA and/or components of the ABA signal transduction pathway. Possible cross-talks between genes involved in wounding and osmotic stress adaptation pathways in tomato are discussed.

Regulation of Ammonium Cellular Levels is An Important Adaptive Trait for the Euhalophytic Behavior of Salicornia europaea.

Salinization of agricultural land is a devastating phenomenon which will affect future food security. Understanding how plants survive and thrive in response to salinity is therefore critical to potentiate tolerance traits in crop species. The halophyte Salicornia europaea has been used as model system for this purpose. High salinity causes NH4+ accumulation in plant tissues and consequent toxicity symptoms that may further exacerbate those caused by NaCl. In this experiment we exposed Salicornia plants to five concentrations of NaCl (0, 1, 10, 50 and 200 mM) in combination with two concentrations of NH4Cl (1 and 50 mM). We confirmed the euhalophytic behavior of Salicornia that grew better at 200 vs. 0 mM NaCl in terms of both fresh (+34%) and dry (+46%) weights. Addition of 50 mM NH4Cl to the growth medium caused a general growth reduction, which was likely caused by NH4+ accumulation and toxicity in roots and shoots. When plants were exposed to high NH4Cl, high salinity reduced roots NH4+ concentration (-50%) compared to 0 mM NaCl. This correlates with the activation of the NH4+ assimilation enzymes, glutamine synthetase and glutamate dehydrogenase, and the growth inhibition was partially recovered. We argue that NH4+ detoxification is an important trait under high salinity that may differentiate halophytes from glycophytes and we present a possible model for NH4+ detoxification in response to salinity.

Physiological Basis of Salt Stress Tolerance in a Landrace and a Commercial Variety of Sweet Pepper (Capsicum annuum L.).

Salt stress is one of the most impactful abiotic stresses that plants must cope with. Plants' ability to tolerate salt stress relies on multiple mechanisms, which are associated with biomass and yield reductions. Sweet pepper is a salt-sensitive crop that in Mediterranean regions can be exposed to salt build-up in the root zone due to irrigation. Understanding the physiological mechanisms that plants activate to adapt to soil salinization is essential to develop breeding programs and agricultural practices that counteract this phenomenon and ultimately minimize yield reductions. With this aim, the physiological and productive performances of Quadrato D'Asti, a common commercial sweet pepper cultivar in Italy, and Cazzone Giallo, a landrace of the Campania region (Italy), were compared under different salt stress treatments. Quadrato D'Asti had higher tolerance to salt stress when compared to Cazzone Giallo in terms of yield, which was associated with higher leaf biomass vs. fruit ratio in the former. Ion accumulation and profiling between the two genoptypes revealed that Quadrato D'Asti was more efficient at excluding chloride from green tissues, allowing the maintenance of photosystem functionality under stress. In contrast, Cazzone Giallo seemed to compartmentalize most sodium in the stem. While sodium accumulation in the stems has been shown to protect shoots from sodium toxicity, in pepper and/or in the specific experimental conditions imposed, this strategy was less efficient than chloride exclusion for salt stress tolerance.