Combined Stress Conditions Research Articles

Exploring Suitability of Salsola imbricata (Fetid Saltwort) for Salinity and Drought Conditions: A Step Toward Sustainable Landscaping Under Changing Climate.

In context of the climate change, major abiotic stresses faced by plants include salt stress and drought stress. Though, plants have similar physiological mechanisms to cope with these salt and drought stresses. The physiological and biochemical response of native plants to the combined application of salinity and drought stresses are still not well-understood. Thus, to investigate the combined effect of salinity and drought stresses, an experiment was conducted on Salsola imbricata with four levels of salinity and four drought intensities under the arid climatic conditions. The experiment was conducted in a randomized complete block design with a split-plot arrangement replicated three times. S. imbricata had been found resistant to different levels of individual and combined salt and drought stresses. S. imbricata survived till the end of the experiment. Salt and water stress did not show any significant effects on shoot weight, shoot length, and root length. The drought stress affected the photosynthetic rate, ion uptake and leaf water potential. However, salt stress helped to counter this effect of drought stress. Thus, drought stress did not affect plant growth, photosynthesis rate, and ion uptake when combined with salt stress. Increased Na+ and Cl− uptake under the salt stress helped in osmotic adjustment. Therefore, the leaf water potential (LWP) decreased with increasing the salt stress from 5 dSm−1 until 15 dSm−1 and increased again at 20 dSm−1. At lower salt stress, ABA and proline content declined with increasing the drought stress. However, at higher salt stress, ABA content increased with increasing the drought stress. In conclusion, the salt stress had been found to have a protective role to drought stress for S. imbricata. S. imbricata utilized inorganic ion for osmotic adjustment at lower salinity stress but also accumulate the organic solutes to balance the osmotic pressure of the ions in the vacuole under combined stress conditions. Due to the physical lush green appearance and less maintenance requirements, S. imbricata can be recommended as a native substitute in landscaping under the salt and drought stresses conditions.

Combining Ability and Heterotic Patterns of Tropical Early-Maturing Maize Inbred Lines under Individual and Combined Heat and Drought Environments.

Information on combining ability and heterotic patterns of multiple stress-tolerant inbred lines are fundamental prerequisites for devising appropriate breeding strategies for the development of climate-resilient maize hybrids. In the present study, we evaluated 150 single cross hybrids derived from the North Carolina Design II (NCD II) along with six commercial checks under terminal drought stress (TDS), heat stress (HS), and combined drought and heat stress (CHDS)conditions. The objectives of the study were to: (i) determine the combining ability of the inbred lines and identify the best testers across the stresses; (ii) classify the inbred lines into heterotic groups (HGs) based on the general combining ability of multiple traits (HGCAMT) and sequencing-based diversity array technology (DArTseq) and (iii) assess the performance and stability of the lines in hybrid combinations. The inbred lines showed significantly (p < 0.01 and p < 0.05) positive and negative general combining ability (GCA) and specific combining ability (SCA) effects for grain yield (GY) and most other measured traits. The inbred line TZEI 135 displayed relatively larger positive GCA effects for GY when mated either as male or female and was identified as the best tester. TZEI 135 × TZEI 182 was identified as the best single-cross tester across environments. Results of the assessment of the relative importance of GCA and SCA effects revealed the predominance of additive gene action over the non-additive. Six HGs of inbreds were identified using the HGCAMT and three, based on the DArTseq marker genetic distance method, were the most efficient. The best hybrids in this study significantly out-yielded the best checks by 21, 46, and 70% under CHDS, HS, and TDS, respectively. These hybrids should be extensively tested in on-farm trials for possible commercialization in sub-Saharan Africa.

Evaluation of wheat genotypes for yield potential under combined drought and heat stress conditions

The combined effects of drought and heat stress severely impact the potential of crop yield. The present study was conducted to determine the tolerant genotypes among 80 wheat genotypes for combined drought and heat stress based on several stress indices. Results showed that grain yield under normal and combined stressed environments was significantly and positively correlated with stress tolerance index (STI) whereas indices like stress susceptibility index (SSI), tolerance (TOL) and reduction (RED) had negative and significant association with grain yield under stressed conditions and significant positive correlation with grain yield under normal conditions. Based on the stress tolerance index, genotypes RW5, WH1142, PBW773, GW463, HD3086 and UP2981 were identified as high yielding as well as stress tolerant, while C306, HD2888, GW477, HD3043, DBW173, JWS825 and MP3288 are promising genotypes to be cultivated under combined drought and heat stress conditions based on stress susceptibility index, tolerance and reduction. The selected genotypes can be further utilized in wheat breeding programmes to develop tolerant cultivars for combined drought and heath stress.

Nitrogen Modulates the Effects of Short-Term Heat, Drought and Combined Stresses after Anthesis on Photosynthesis, Nitrogen Metabolism, Yield, and Water and Nitrogen Use Efficiency of Wheat

More frequent and more intense heat waves and greater drought stress will occur in the future climate environment. Short-term extreme heat and drought stress often occur simultaneously after winter wheat anthesis, which has become the major constraint threatening future wheat yield. In this study, short-term heat, drought and their combination stress were applied to wheat plants after anthesis, and all wheat plants were restored to the outdoor normal temperature and full watering after stress treatment. The aim of the current study was to evaluate the role of nitrogen (N) in modulating the effects of post-anthesis short-term heat, drought and their combination stress on photosynthesis, N metabolism-related enzymes, the accumulation of N and protein and growth, as well as on the yield and water (WUE) and N use efficiency (NUE) of wheat after stress treatment. The results showed that compared with low N application (N1), medium application (N2) enhanced the activities of nitrate reductase (NR) and glutamine synthase (GS) in grains under post-anthesis heat and drought stress alone, which provided a basis for the accumulation of N and protein in grains at the later stage of growth. Under post-anthesis individual stresses, N2 or high application (N3) increased the leaf photosynthetic rate (An), PSII photochemical efficiency and instantaneous WUE compared with N1, whereas these parameters were usually significantly improved by N1 application under post-anthesis combined stress. The positive effect of increased An by N application on growth was well represented in a higher green leaf area, aboveground dry mass and plant height, and the variation in An can be explained more accurately by the N content per unit leaf area. Short-term heat, drought and combined stress after anthesis resulted in a pronounced decrease in yield by reducing grain number per spike and thousand kernel weight. The reduction in NUE under combined stress was higher than that under individual heat and drought stress. Compared with N1, N2 or N3 application significantly prevented the decrease in yield and NUE caused by post-anthesis heat and drought stress alone. However, N1 application was conducive to improving the productivity, WUE and NUE of wheat when exposed to post-anthesis combined stress. The current data indicated that under short-term individual heat and drought stress after anthesis, appropriately increasing N application effectively improved the growth and physiological activity of wheat compared with N1, alleviating the reduction in yield, WUE and NUE. However, under combined stress conditions, reducing N application (N1) may be a suitable strategy to compensate for the decrease in yield, WUE and NUE.

Effect of Drought and Low P on Yield and Nutritional Content in Common Bean

Common bean (Phaseolus vulgaris L.) production in the tropics typically occurs in rainfed systems on marginal lands where yields are low, primarily as a consequence of drought and low phosphorus (P) availability in soil. This study aimed to investigate the physiological and chemical responses of 12 bush bean genotypes for adaptation to individual and combined stress factors of drought and low P availability. Water stress and P deficiency, both individually and combined, decreased seed weight and aboveground biomass by ∼80%. Water deficit and P deficiency decreased photosynthesis and stomatal conductance during plant development. Maximum rates of carboxylation, electron transport, and triose phosphate utilization were superior for two common bean genotypes (SEF60 and NCB226) that are better adapted to combined stress conditions of water deficit and low P compared to the commercial check (DOR390). In response to water deficit treatment, carbon isotope fractionation in the leaf tissue decreased at all developmental stages. Within the soluble leaf fraction, combined water deficit and low P, led to significant changes in the concentration of key nutrients and amino acids, whereas no impact was detected in the seed. Our results suggest that common bean genotypes have a degree of resilience in yield development, expressed in traits such as pod harvest index, and conservation of nutritional content in the seed. Further exploration of the chemical and physiological traits identified here will enhance the resilience of common bean production systems in the tropics.

Morphological, physiological and biochemical responses to combined cadmium and drought stress in radish (Raphanus sativus L.)

Drought and heavy metal stress are among the most important stress factors that negatively affect plant growth. This study was carried out to determine the individual and combined effects of cadmium (Cd) and drought stress on growth (plant leaf area, stem and root diameter, shoot and root fresh weight, shoot and root dry weight), physiological [electrolyte leakage (EL), leaf relative water content (LRWC)] and biochemical [antioxidant enzyme activity, hydrogen peroxide (H2O2), malondialdehyde (MDA), proline, sucrose and mineral element content] parameters of radish. In the study, four Cd concentrations (0 mg kg−1, 100 mg kg−1, 150 mg kg−1 and 200 mg kg−1), three irrigation levels (100%, 75% and 50% of field capacity—FC) were used. Leaf area, stem and root diameter, shoot and root fresh weight, shoot and root dry weight, LRWC, chlorophyll a, chlorophyll b and total chlorophyll content decreased with increased level of drought and Cd stress, but EL has increased. The effect of water deficit on these parameters was more detrimental than heavy metal stress; however, the stress-related damage was greater under combined stress conditions. In addition, H2O2, MDA, proline and sucrose content of radish leaves increased with increased water deficit and Cd stress levels. POD, CAT and SOD enzyme activities of radish leaves under combined stresses increased more than individual stress conditions. There was a significant increase in the content of Cd in the plant leaves and roots under Cd stress compared to the control. This increase in leaves was more pronounced than roots. Although individual drought and Cd stress negatively influenced radish growth and development, the damage was greater with the simultaneous occurrence of these two stress factors.

Transcriptomic Reprogramming, Alternative Splicing and RNA Methylation in Potato (Solanum tuberosum L.) Plants in Response to Potato Virus Y Infection.

Plant-virus interactions are greatly influenced by environmental factors such as temperatures. In virus-infected plants, enhanced temperature is frequently associated with more severe symptoms and higher virus content. However, the mechanisms involved in controlling the temperature regulation of plant-virus interactions are poorly characterised. To elucidate these further, we analysed the responses of potato plants cv Chicago to infection by potato virus Y (PVY) at normal (22 °C) and elevated temperature (28 °C), the latter of which is known to significantly increase plant susceptibility to PVY. Using RNAseq analysis, we showed that single and combined PVY and heat-stress treatments caused dramatic changes in gene expression, affecting the transcription of both protein-coding and non-coding RNAs. Among the newly identified genes responsive to PVY infection, we found genes encoding enzymes involved in the catalysis of polyamine formation and poly ADP-ribosylation. We also identified a range of novel non-coding RNAs which were differentially produced in response to single or combined PVY and heat stress, that consisted of antisense RNAs and RNAs with miRNA binding sites. Finally, to gain more insights into the potential role of alternative splicing and epitranscriptomic RNA methylation during combined stress conditions, direct RNA nanopore sequencing was performed. Our findings offer insights for future studies of functional links between virus infections and transcriptome reprogramming, RNA methylation and alternative splicing.

Plant growth promoting bacteria improve growth and phytostabilization potential of Zea mays under chromium and drought stress by altering photosynthetic and antioxidant responses

Drought in heavy metal polluted arid and semiarid regions severely inhibits the plant growth and phytoremediation potential by affecting photosynthesis, antioxidant defense mechanism, and other biochemical processes. In the present study, we explored the role of plant growth-promoting bacteria (PGPB) on Zea mays growth and phytoremediation efficiency in Chromium (Cr) contaminated soils under drought stress by assessing plant stress tolerance, photosynthetic gas exchange activities, chlorophyll fluorescence, and Cr accumulation. Two efficient Cr and drought resistant PGPB with the potential to reduce Cr(VI) to Cr(III) and produce plant growth-promoting metabolites even under Cr, drought, or Cr+drought stress conditions were isolated and identified as Providencia sp. (TCR05) and Proteus mirabilis (TCR20). In pot experiments, the inoculation of TCR05 and TCR20 increased the plant growth, pigments, protein, phenolics, and relative water content and decreased the lipid peroxidation, proline, and superoxide dismutase activity under Cr, drought, or Cr+drought conditions. Irrespective of stress treatment, TCR05 and TCR20 also improved plant photosynthetic efficiency by increasing the CO 2 assimilation rate, stomatal conductance to water vapor, transpiration rate, maximum quantum efficiency of PSII, actual quantum efficiency of PSII, electron transport rate, photochemical quenching, reducing the internal CO 2 concentration and non-photochemical quenching. Besides, the PGPB decreased the translocation of Cr through immobilization of Cr in root. These results denoted that strains TCR05 and TCR20 could be a capable bio-inoculant for improving plant growth and phytostabilization practices in Cr contaminated sites even under water-limited conditions. • Potential Cr(VI) reducing MST-PGPB strains TCR05 and TCR20 were isolated. • MST-PGPB enhanced stress tolerance of Z. mays under combined stress conditions. • PGPB inoculation improved the PSII performance of Z. mays under combined stresses. • PGPB inoculation improved Cr phytostabilization under combined stress conditions.

Drought and heat stress mitigation in rice for yield improvement using temperature induction response technique

The investigation was conducted in two experiments in the College of Agriculture Vellayani, Kerala Agricultural University. First experiment was done to standardize the Temperature Induction Response (TIR) protocol for rice. Second experiment was conducted to study the effect of TIR technique on yield and yield attributes under drought, heat and combined drought and heat stress; 52°C for 3 h was selected as lethal temperature and 32–42°C for 5h & 42–52°C for 30 min were selected as induction temperatures. Results revealed that TIR induction had significant effect on yield and yield attributes under combined drought and heat stress. TIR induced plants without any stress showed the highest growth and yield attributes. Performance of rice genotypes Nagina-22 and Apo improved under combined stress condition using TIR induced seedlings. Apart from these two genotypes, Ptb-15 and Ptb-7 recorded better performance under heat stress and drought, respectively. For combined stress, Ptb-30 and Ptb-15 showed better performance compared to other genotypes. Ptb39 was identified as the most susceptible genotype for both drought and heat stress conditions, but TIR induced plants of susceptible genotype showed improved stress tolerance. Hence, this technique can be used as a potential tool for improving the performance of high yielding abiotic stress susceptible genotypes under stress conditions.

Physiological Characteristics of Cultivated Tepary Bean (Phaseolus acutifolius A. Gray) and Its Wild Relatives Grown at High Temperature and Acid Soil Stress Conditions in the Amazon Region of Colombia.

Common bean (Phaseolus vulgaris L.) is sensitive to different types of abiotic stresses (drought, high temperature, low soil fertility, and acid soil), and this may limit its adaptation and consequently to its yield under stress. Because of this, a sister species, tepary bean (Phaseolus acutifolius A. Gray), has recently gained attention in breeding for improved abiotic stress tolerance in common bean. In this study, we evaluated the adaptation of 302 accessions of tepary bean (Phaseolus acutifolius A. Gray) and its wild relatives (grouped in four types of tepary bean genetic resource: cultivated, acutifolius regressive, acutifolius wild, tenuifolius wild) when grown under high temperature and acid soil conditions with aluminum toxicity in the Amazon region of Colombia. Our objective was to determine differences among four types of tepary bean genetic resource in their morpho-phenological, agronomic, and physiological responses to combined high temperature and acid soil stress conditions. We found that cultivated P. acutifolius var acutifolius presented a greater number of pods per plant, as well as larger seeds and a greater number of seeds per pod. Some traits, such as root biomass, days to flowering and physiological maturity, specific leaf area, and stomatal density, showed significant differences between types of tepary bean genetic resource, probably contributing to difference in adaptation to combined stress conditions of high temperature and acid soil conditions. The photochemical quenching (qP) was higher in cultivated P. acutifolius var. acutifolius, while energy dissipation by non-photochemical quenching (NPQ) in the form of heat and the coefficient of non-photochemical dissipation (qN) were higher in acutifolius regressive and tenuifolius wild accessions. We have identified 6 accessions of cultivated and 19 accessions of tenuifolius wild that exhibited grain yields above 1800 kg ha−1. These accessions could be suitable to use as parents to improve dry seed production of tepary bean under combined stress conditions of high temperature and acid soil.

Combined Stress Conditions in Melon Induce Non-additive Effects in the Core miRNA Regulatory Network.

Climate change has been associated with a higher incidence of combined adverse environmental conditions that can promote a significant decrease in crop productivity. However, knowledge on how a combination of stresses might affect plant development is still scarce. MicroRNAs (miRNAs) have been proposed as potential targets for improving crop productivity. Here, we have combined deep-sequencing, computational characterization of responsive miRNAs and validation of their regulatory role in a comprehensive analysis of response of melon to several combinations of four stresses (cold, salinity, short day, and infection with a fungus). Twenty-two miRNA families responding to double and/or triple stresses were identified. The regulatory role of the differentially expressed miRNAs was validated by quantitative measurements of the expression of the corresponding target genes. A high proportion (ca. 60%) of these families (mainly highly conserved miRNAs targeting transcription factors) showed a non-additive response to multiple stresses in comparison with that observed under each one of the stresses individually. Among those miRNAs showing non-additive response to stress combinations, most interactions were negative, suggesting the existence of functional convergence in the miRNA-mediated response to combined stresses. Taken together, our results provide compelling pieces of evidence that the response to combined stresses cannot be easily predicted from the study individual stresses.

Abiotic stress-by-competition interactions drive hormone and nutrient changes to regulate Suaeda salsa growth

During the growth cycle, complex and variable environmental conditions, such as salinity, moisture, nutrients, and plant-plant interactions, may prompt plants to modulate ecological strategies. As a typical halophyte, the response mechanism and adaptation strategy of Suaeda salsa to various abiotic stress-by-competition interactions are still unclear. In this study, we aimed to explore the responses of S. salsa to combined abiotic stress and competition conditions to gain further insights into the ecological adaptation of halophytes to stress conditions. In this study, we aimed to explore the responses of S. salsa to combined abiotic stress and competition conditions to gain further insights into the ecological adaptation of halophytes to stress conditions. In a pot experiment, we set five density gradients of 1, 3, 6, 9, and 12 plants and conducted salt and drought stress experiments to explore the ecological adaptation strategies under abiotic stress-by-competition and the direct and/or indirect effects of key endogenous hormones and nutrients on plant growth. The results demonstrated that drought and planting density were the main environmental factors that restricted growth. Drought decreased biomass accumulation and competition intensity and delayed reproductive phenology and senescence. Competition promoted early anthesis and fructescence and reduced the vegetative organ to reproductive organ ratio to improve fitness. Changes in hormone and nutrient levels driven by the environment directly and/or indirectly affected growth independently and/or jointly. Total leaf phosphorus content and the endogenous hormone strigolactones directly affected biomass in different interaction modes and had positive and negative effects, respectively. This study improves our understanding of the importance of hormones and nutrients in plant ecological adaptation strategies and provides an effective reference for explaining the physiological mechanisms of plant ecological adaptation.

Physiological Variation in Response to Vibrio and Hypoxia by Aquacultured Eastern Oysters in the Southeastern United States.

Eastern oysters (Crassostrea virginica) have long been recognized as model organisms of extreme environmental tolerance, showing resilience to variation in temperature, salinity, hypoxia, and microbial pathogens. These phenotypic responses, however, show variability between geographic locations or habitats (e.g., tidal). Physiological, morphological, and genetic differences occur in populations throughout a species' geographical range, which may have been shaped by regional abiotic and biotic variations. Few studies of C. virginica have explored the combined factors of physiological mechanisms of divergent phenotypes between locations and the genetic relationships of individuals between these locations. To characterize genetic relationships of four locations with aquacultured oysters along the North Carolina and Virginia coast, we sequenced a portion of cytochrome oxidase subunit I (COI) that revealed significant variation in haplotype distribution between locations. We then measured mitochondrial physiology and expression of the innate immunity response of hemocytes to lab acclimation and combined stress conditions to compare basal expression and stress response in oysters between these locations. For stress sensing genes, toll-like receptors had the strongest location-specific response to hypoxia and Vibrio, whereas mannose receptor and a stress-receptor were specific to hypoxia and bacteria, respectively. The expression of stress response genes also showed location-specific and stressor-specific changes in expression, particularly for big defensin and the complement gene Cq3. Our results further suggested that genetic similarity of oysters from different locations was not clearly related to physiological and molecular responses. These results are informative for understanding the range of physiological plasticity for stress responses in this commercially important oyster species. They also have implications in the oyster farming industry as well as conservation efforts to restore endangered native oyster beds.

Modeling of dowel action for cast-in and post-installed anchors considering bond property

In reinforced concrete structures, cast-in anchors are applied to beam–column or slab–beam joints. Furthermore, in seismically strengthened structures, post-installed anchors are used to connect new members to existing members. These anchors are subjected to shear and tensile stresses during an earthquake. However, a mechanical model that can estimate the behavior of these anchors when subjected to combined stress has not yet been proposed. Therefore, in this study, various anchors were tested under combined stress conditions. The test parameters were the type of anchorage method, shape of anchor bolt, anchorage length, hole diameter of the drilling, type of adhesive, and tensile stress ratio. It was observed that the shear force of the post-installed anchors was larger than that of the cast-in anchors. Moreover, as the diameter of the hole increased, the shear force also increased. Subsequently, the mechanical model, which was proposed for a post-installed anchor in a previous study, was modified for application to various anchors. By considering the diameter of the hole in the bearing resistance and introducing the bond strength to catenary action, the test results of the various anchors could be reasonably estimated.

Foliar Growth Regulator Sprays Induced Tolerance to Combined Heat Stress by Enhancing Physiological and Biochemical Responses in Rice.

Rice yield has decreased due to climate variability and change in Colombia. Plant growth regulators have been used as a strategy to mitigate heat stress in different crops. Therefore, this study aimed to evaluate the effect of foliar applications of four growth regulators [auxins (AUX), brassinosteroids (BR), cytokinins (CK), or gibberellins (GA)] on physiological (stomatal conductance, total chlorophyll content, Fv/Fm ratio, plant canopy temperature, and relative water content) and biochemical (Malondialdehyde (MDA) and proline contents) variables in two commercial rice genotypes exposed to combined heat stress (high day and nighttime temperatures). Two separate experiments were carried out using plants of two rice genotypes, Fedearroz 67 (“F67”) and Fedearroz 2000 (“F2000”) for the first and second experiments, respectively. Both trials were analyzed together as a series of experiments. The established treatments were as follows: absolute control (AC) (rice plants grown under optimal temperatures (30/25°C day/nighttime temperatures), heat stress control (SC) [rice plants only exposed to combined heat stress (40/30°C)], and stressed rice plants and sprayed twice (5 days before and after heat stress) with a plant growth regulator (stress+AUX, stress+BR, stress+CK, or stress+GA). The results showed that foliar CK sprays enhanced the total chlorophyll content in both cultivars (3.25 and 3.65 mg g−1 fresh weight for “F67” and “F2000” rice plants, respectively) compared to SC plants (2.36 and 2.56 mg g−1 fresh weight for “F67,” and “F2000” rice plants, respectively). Foliar CK application also improved stomatal conductance mainly in “F2000” rice plants compared to their heat stress control (499.25 vs.150.60 mmol m−2s−1). Foliar BR or CK sprays reduced plant canopy temperature between 2 and 3°C and MDA content in plants under heat stress. The relative tolerance index suggested that foliar CK (97.69%), and BR (60.73%) applications helped to mitigate combined heat stress mainly in “F2000” rice plants. In conclusion, foliar BR or CK applications can be considered an agronomic strategy to help to ameliorate the negative effect of combined heat stress conditions on the physiological behavior of rice plants.

Morpho-Physio-Biochemical and Molecular Responses of Maize Hybrids to Salinity and Waterlogging during Stress and Recovery Phase.

Maize is one of the most economically important cereal crops worldwide. Salinity coupled with waterlogging is a major challenge for successful crop production. Understanding the underlying mechanisms and impacts of individual and combined salinity and waterlogging stress on the morpho-physio-biochemical and molecular responses and oxidative metabolism of maize during stress and recovery periods is essential. The present study was carried out to assess the response of four hybrid maize cultivars viz. DK-6142, FH-1231, FH-949, and MALKA-2016 under individual and combined salinity and waterlogging conditions. The treatments comprised the control (no stress), NaCl (salinity with 10 dSm−1), WL (waterlogged conditions with 3 cm flooding), and NaCl + WL (combined salinity and waterlogging stress). The data regarding morpho-physiological attributes were collected at 22 days after sowing (DAS; stress phase) and 30 DAS (recovery phase). The results revealed that both stresses, either individually or in combination, substantially reduced the root-shoot length, root-shoot fresh and dry weights, leaf width, and the number of leaves per plant as well as the leaf chlorophyll (Chl) and carotenoids contents; however, the inhibitory effects were more severe in combined stresses than for individual stress factors in many cultivars. Both individual and combined stress conditions enhanced hydrogen peroxide (H2O2) accumulation, whereas the antioxidant enzyme activities, i.e., superoxide dismutase (SOD), peroxidase (POD) catalase (CAT), and ascorbate peroxidase (APX), remained higher under stress conditions compared to the control. The expression levels of antioxidant genes (CAT and POD) were also upregulated under stress conditions. All of the cultivars recovered better from individual stresses than combined stress conditions; however, the hybrid DK-6142 performed better than the other maize hybrids under stress conditions and showed faster recovery.

Stress markers and physiochemical responses of the Mediterranean shrub Phillyrea angustifolia under current and future drought and ozone scenarios

Mediterranean plants are particularly threatened by the exacerbation of prolonged periods of summer drought and increasing concentrations of ground-level ozone (O3). The aims of the present study were to (i) test if selected markers (i.e., reactive oxygen species, ROS; malondialdehyde, MDA; photosynthetic pigments) are able to discriminate the oxidative pressure due to single and combined stress conditions, and (ii) elucidate the physiochemical adjustments adopted by Phillyrea angustifolia (evergreen woody species representative of the maquis, also known as narrow-leaved mock privet) to perceive and counter to drought and/or O3. Plants were grown from May to October under the combination of two levels of water irrigation [i.e., well-watered (WW) and water-stressed (WS)] and three levels of O3 [i.e., 1.0, 1.5 and 2.0 times the ambient air concentrations, i.e. AA (current O3 scenario), 1.5 × AA and 2.0 × AA (future O3 scenarios), respectively], using a new-generation O3 Free Air Controlled Exposure (FACE) system. Overall, this species appeared relatively sensitive to drought (e.g., net CO2 assimilation rate and stomatal conductance significantly decreased, as well as total chlorophyll and carotenoid contents), and tolerant to O3 (e.g., as confirmed by the absence of visible foliar injury, the unchanged values of total carotenoids, and the detrimental effects on stomatal conductance, total chlorophylls and terpene emission only under elevated O3 concentrations). The combination of both stressors led to harsher oxidative stress. Only when evaluated together (i.e., combining the information provided by the analysis of each stress marker), ROS, MDA and photosynthetic pigments, were suitable stress markers to discriminate the differential oxidative stress induced by drought and increasing O3 concentrations applied singly or in combination: (i) all these stress markers were affected under drought per se; (ii) hydrogen peroxide (H2O2) and MDA increased under O3per se, following the gradient of O3 concentrations (H2O2: about 2- and 4-fold higher; MDA: +22 and + 91%; in 1.5 × AA_WW and 2.0 × AA_WW, respectively); (iii) joining together the ROS it was possible to report harsher effects under 2.0 × AA_WS and 1.5 × AA_WS (both anion superoxide and H2O2 increased) than under 2.0 × AA_WW (only H2O2 increased); and (iv) MDA showed harsher effects under 2.0 × AA_WS than under 1.5 × AA_WS (increased by 49 and 18%, respectively). Plants activated physiological and biochemical adjustments in order to partially avoid (e.g., stomatal closure) and tolerate (e.g., increased terpene emission) the effects of drought when combined with increasing O3 concentrations, suggesting that the water use strategy (isohydric) and the sclerophyllous habit can further increase the plant tolerance to environmental constraints in the Mediterranean area.

Differential Response to Single and Combined Salt and Heat Stresses: Impact on Accumulation of Proteins and Metabolites in Dead Pericarps of Brassica juncea.

Dead organs enclosing embryos, such as seed coats and pericarps, are emerging as important maternally-derived components of the dispersal unit that affect seed performance and fate. In the face of climate change and increased incidents of heatwaves, we sought to investigate the effect of salinity (S), short episodes of high temperature (HS), and combination of S + HS (SHS), at the reproductive phase, on the properties of dead pericarps of Brassica juncea. Proteome and metabolome analyses revealed multiple proteins and metabolites stored in dead pericarps whose levels and composition were altered under single and combined stress conditions. The protein profile of SHS showed a higher correlation with salt than with HS indicating the dominant effect of salt over heat stress. On the other hand, the analysis of metabolites showed that the profile of SHS has better correlation with HS than with salt. The integration of metabolic and proteomic data showed that changes in TCA cycle intermediates and certain amino acids (e.g., proline) under salt treatments (S and SHS) are highly correlated with changes in proteins involved in their biosynthetic pathways. Thus, accumulation of proteins and metabolites in dead pericarps is differently affected by single and combination of salt and heat stresses. Salinity appears to dominate plant response to combined stresses at the protein level, while heat appears to be the major factor affecting metabolite accumulation in dead pericarps.

Effects of Nitrogen and Water Deficiency on Agronomic Properties, Root Characteristics and Expression of Related Genes in Soybean

Drought and insufficient nutrient supply are the main limiting factors for field crop production; therefore, the present study aimed to investigate the responses of four registered soybean varieties to limited nitrogen (N) supply in combination with drought stress. Plants were grown in tubes filled with silica sand, under open-air conditions. Water shortage was initiated at the three-leaf stage by providing 50% of water, and N deficiency was obtained by reducing the N content of the half-strength Hoagland solution by 50%. N deficiency did not influence the grain yield, while it significantly increased the root dry biomass in Boglár and Pannónia Kincse. Compared with nitrogen supply, the effects of the water shortage were dominant in root development. The expression levels of the investigated genes also showed genotypic variations. The expression of the Inducible nitrate reductase1 gene increased under N-deficient conditions in Boglár and decreased in Pannónia Kincse under drought conditions. The expression level of the aldehyde dehydrogenase gene and abscisic acid 8’-hydroxylase 3 increased under combined stress conditions. Summarising the agronomic and physiological characteristics, Boglár and Sinara were sensitive to drought, Bagera was sensitive to N deficiency but produced the highest yield under limited watering in each nitrogen treatment, while Pannónia Kincse was tolerant to nitrogen deficiency under well-watered conditions.

Exogenous silicon and hydrogen sulfide alleviates the simultaneously occurring drought stress and leaf rust infection in wheat

Silicon (Si) and hydrogen sulfide (H2S) are known to enhance plant defense against multiple stresses. Current study was conducted to investigate the application of Si and H2S alone as well as in combination, improved physiological resilience of wheat plants to drought stress (DS) and pathogen-Puccinia triticina (Pt) infection. We aimed to increase the wheat plant growth and to enhance the DS tolerance and Pt resistance with the concurrent applications of H2S and Si. In the first experiment, we selected the best growth enhancing concentration of H2S (0.3 mM) and Si (6 mM) to further investigate their tolerance and resistance potential in the pot experiment under DS and pathogen infection conditions. The obtained results reveal that DS has further increased the susceptibility of wheat plants to leaf rust pathogen infection while, the sole application of Si and the simultaneous exogenous treatments of H2S + Si enhanced the plant growth, decreased disease incidence, and significantly improved tolerance and defense mechanisms of wheat under individual and interactive stress conditions. The exogenous treatment of H2S + Si improved the growth criteria, photosynthetic pigments, osmoprotectants, and defense related enzyme activities. The same treatment also reinforced the endogenous H2S, Si, ABA and SA contents while decreased the disease incidence and oxidative stress indicators under individual and combined stress conditions. Overall, results from this study presents the influence of combined drought and P. triticina stress in wheat and reveal the beneficial impacts of concurrent exogenous treatment of H2S + Si to mitigate the drought and pathogen (P. triticina) induced adverse effects.