Insights into the physiological and biochemical responses of peanut plants under combined arsenic and flooding stress.

Plant responses to a combination of drought and bacterial pathogen infection, an agronomically important and altogether a new stress, are not well-studied. While occurring concurrently, these two stresses can lead to synergistic or antagonistic effects on plants due to stress-interaction. It is reported that plant responses to the stress combinations consist of both strategies, unique to combined stress and those shared between combined and individual stresses. However, the combined stress response mechanisms governing stress interaction and net impact are largely unknown. In order to study these adaptive strategies, an accurate and convenient methodology is lacking even in model plants like Arabidopsis thaliana. The gradual nature of drought stress imposition protocol poses a hindrance in simultaneously applying pathogen infection under laboratory conditions to achieve combined stress. In present study we aimed to establish systematic combined stress protocol and to study physiological responses of the plants to various degrees of combined stress. Here, we have comprehensively studied the impact of combined drought and Pseudomonas syringae pv. tomato DC3000 infection on A. thaliana. Further, by employing different permutations of drought and pathogen stress intensities, an attempt was made to dissect the contribution of each individual stress effects during their concurrence. We hereby present two main aspects of combined stress viz., stress interaction and net impact of the stress on plants. Mainly, this study established a systematic protocol to assess the impact of combined drought and bacterial pathogen stress. It was observed that as a result of net impact, some physiological responses under combined stress are tailored when compared to the plants exposed to individual stresses. We also infer that plant responses under combined stress in this study are predominantly influenced by the drought stress. Our results show that pathogen multiplication was reduced by drought stress in combined stressed plants. Combined stressed plants also displayed reduced ROS generation and declined cell death which could be attributed to activation of effective basal defense responses. We hypothesize a model on ABA mediated gene regulation to partly explain the possible mechanistic basis for reduced in planta bacterial numbers under combined stress over individual pathogen stress.

The present study was carried out to investigate the effect of individual drought, heat, and combined drought and heat stress on tomato plants. Combined stress resulted in the higher accumulation of Proline (101.9%), MDA (38.55%), H2O2 (101.19%), and lower levels of RWC (53.84%). Individual drought and heat stress decreased photosynthetic pigments like total chlorophyll content by (45.45%) and (25.35%), respectively, higher rates of pigment reduction (79.42%) were observed under combined drought and heat stress. Combined stress decreased PSII efficiency (Fv/Fm), quantum yield (ΦPSII), and photochemical efficiency (qp) and increased non-photochemical quenching (NPQ) levels. Moreover, the gas exchange parameters E, A, and Pn decreased by 5.36%, 36.45%, and 51.00%, respectively, in comparison to control plants. Antioxidant enzymes, SOD, APX, CAT, and GR showed a two- to threefold increase under combined drought and heat stress; however, the non-enzymatic antioxidants AsA and GSH displayed one-twofold increase under combined stress. Moreover, 2- to 2.5-fold decrease was observed in MDHAR and DHAR enzyme transcripts under combined stress conditions. The transcripts corresponding to AsA-GSH pathway enzymes SOD, APX, GR, DHAR, and MDHAR were up-regulated by 8- to 12-fold under combined drought and heat. Furthermore, DREB and LEA transcripts were up-regulated under drought and combined stress and down-regulated under drought stress. In the same manner, HSP70 and HSP90 transcripts were up-regulated under heat and combined stress; however, the transcription levels got down-regulated under drought stress. Additionally, rbcL and RCA transcripts were down-regulated especially under combined stress in comparison to individual drought and heat conditions. PSIP680 relative expression levels were up-regulated under drought stress; however, the transcripts were down-regulated under heat and combined stress. Taken together, the results suggest that the combined stress has a predominant effect over individual stress.

Role of Xanthoceras sorbifolium MYB44 in tolerance to combined drought and heat stress via modulation of stomatal closure and ROS homeostasis

Thriving in adversity: Understanding how maize seeds respond to the challenge of combined cold and high humidity stress.

AtGBF3 confers tolerance to Arabidopsis thaliana against combined drought and Pseudomonas syringae stress

Differential regulation of the banana stress NAC family by individual and combined stresses of drought and heat in susceptible and resistant genotypes

In nature plants are often simultaneously challenged by different biotic and abiotic stresses. Although the mechanisms underlying plant responses against single stress have been studied considerably, plant tolerance mechanisms under combined stress is not understood. Also, the mechanism used to combat independently and sequentially occurring many number of biotic and abiotic stresses has also not systematically studied. From this context, in this study, we attempted to explore the shared response of sunflower plants to many independent stresses by using meta-analysis of publically available transcriptome data and transcript profiling by quantitative PCR. Further, we have also analyzed the possible role of the genes so identified in contributing to combined stress tolerance. Meta-analysis of transcriptomic data from many abiotic and biotic stresses indicated the common representation of oxidative stress responsive genes. Further, menadione-mediated oxidative stress in sunflower seedlings showed similar pattern of changes in the oxidative stress related genes. Based on this a large scale screening of 55 sunflower genotypes was performed under menadione stress and those contrasting in oxidative stress tolerance were identified. Further to confirm the role of genes identified in individual and combined stress tolerance the contrasting genotypes were individually and simultaneously challenged with few abiotic and biotic stresses. The tolerant hybrid showed reduced levels of stress damage both under combined stress and few independent stresses. Transcript profiling of the genes identified from meta-analysis in the tolerant hybrid also indicated that the selected genes were up-regulated under individual and combined stresses. Our results indicate that menadione-based screening can identify genotypes not only tolerant to multiple number of individual biotic and abiotic stresses, but also the combined stresses.

Purslane (Portulaca oleracea L.) is a fleshy herbaceous plant. So far, little information is available on the response of this plant to combined drought and heat stress. In this study, changes in physiological and metabolic levels were characterized after treatments with drought, heat and combined stresses. Both individual and combined stress treatments increased malondialdehyde (MDA), electrolyte leakage (EL), and activities of superoxide dismutase (SOD), peroxidase (POD), while declined chlorophyll content. No significant differences were found between control and treatments in leaf water content (LWC) and catalase (CAT) activity. Additionally, 37 metabolic compounds were detected in purslane. Through pathway analysis, 17 metabolites were directly involved in the glycolysis metabolic pathway. The present study indicated that combined drought and heat stress caused more serious damage in purslane than individual stress. To survive, purslane has a high capability to cope with environmental stress conditions through activation of physiological and metabolic pathways.

Global transcriptome studies demonstrated the existence of unique plant responses under combined stress which are otherwise not seen during individual stresses. In order to combat combined stress plants use signaling pathways and ‘cross talk’ mediated by hormones involved in stress and growth related processes. However, interactions among hormones’ pathways in combined stressed plants are not yet known. Here we studied dynamics of different hormones under individual and combined drought and pathogen infection in Arabidopsis thaliana by liquid chromatography-mass spectrometry (LC-MS) based profiling. Our results revealed abscisic acid (ABA) and salicylic acid (SA) as key regulators under individual drought and pathogen stress respectively. Under combined drought and host pathogen stress (DH) we observed non-induced levels of ABA with an upsurge in SA and jasmonic acid (JA) concentrations, underscoring their role in basal tolerance against host pathogen. Under a non-host pathogen interaction with drought (DNH) stressed plants, ABA, SA and JA profiles were similar to those under DH or non-host pathogen alone. We propose that plants use SA/JA dependent signaling during DH stress which antagonize ABA biosynthesis and signaling pathways during early stage of stress. The study provides insights into hormone modulation at different time points during combined stress.

Combined transcriptome and metabolome analysis revealed the toxicity mechanism of individual or combined of microplastic and salt stress on maize.

In this study, we aimed to identify differentially accumulated proteins (DAPs) involved in PEG mock osmotic stress, cadmium (Cd2+) stress, and their combined stress responses in Brachypodium distachyon seedling roots. The results showed that combined PEG and Cd2+ stresses had more significant effects on Brachypodium seedling root growth, physiological traits, and ultrastructures when compared with each individual stress. Totally, 106 DAPs were identified that are responsive to individual and combined stresses in roots. These DAPs were mainly involved in energy metabolism, detoxification and stress defense and protein metabolism. Principal component analysis revealed that DAPs from Cd2+ and combined stress treatments were grouped closer than those from osmotic stress treatment, indicating that Cd2+ and combined stresses had more severe influences on the root proteome than osmotic stress alone. Protein–protein interaction analyses highlighted a 14-3-3 centered sub-network that synergistically responded to osmotic and Cd2+ stresses and their combined stresses. Quantitative real-time polymerase chain reaction (qRT-PCR) analysis of 14 key DAP genes revealed that most genes showed consistency between transcriptional and translational expression patterns. A putative pathway of proteome metabolic changes in Brachypodium seedling roots under different stresses was proposed, which revealed a complicated synergetic responsive network of plant roots to adverse environments.

Several studies regarding the imposition of stresses simultaneously in plants have shown that plant responses are different under individual and combined stress. Pathogen infection in combination with drought can act both additively and antagonistically, suggesting a tailored-made plant response to these stresses. The aforementioned combination of stresses can be considered as one of the most important factors affecting global crop production. In the present research we studied eggplant responses to simultaneous Verticillium dahliae infection and drought with respect to the application of the individual stresses alone and investigated the extent to which these responses were cultivar dependent. Two eggplant cultivars (Skoutari and EMI) with intermediate resistance to V. dahliae were subjected to combined stress for a 3-week period. Significant differences in plant growth, several physiological and biochemical parameters (photosynthesis rate, leaf gas exchanges, Malondialdehyde, Proline) and gene expression, were found between plants subjected to combined and individual stresses. Furthermore, plant growth and molecular (lipid peroxidation, hydrogen peroxide, gene expression levels) changes highlight a clear discrimination between the two cultivars in response to simultaneous V. dahliae infection and drought. Our results showed that combined stress affects significantly plants responses compared to the application of individual stresses alone and that these responses are cultivar dependent.

Climate change exacerbates combined environmental stresses, leading to significant crop losses globally. This study investigated the physiological and metabolomic responses of adzuki bean (Vigna angularis) leaves to individual and combined chilling-waterlogging stresses during the flowering stage. Results demonstrated that both stresses significantly inhibited photosynthesis, elevated reactive oxygen species accumulation, and induced membrane lipid peroxidation. Waterlogging exhibited more severe impacts, triggering extreme ABA accumulation and plant death at 4 days post-treatment, resulting in total yield loss. Notably, combined stresses induced antagonistic effects, reducing photosynthetic decline by 14.10-32.40% and mitigating oxidative damage by 5.79-10.75% compared to waterlogging alone after 4 days. Metabolomic analysis revealed that combined stress activated more metabolic pathways than individual stress, including flavone/flavonol biosynthesis and cGMP-PKG signaling, which are critical for plant adaptation. This study provides valuable insights into the physiological and metabolic mechanisms underlying adzuki bean's response to combined chilling-waterlogging stress.

Dissecting the molecular responses of lentil to individual and combined drought and heat stresses by comparative transcriptomic analysis

In tropics, combined stresses of drought and heat often reduce crop productivity in plants like Musa acuminata L. We compared responses of two contrasting banana genotypes, namely the drought-sensitive Grand Nain (GN; AAA genome) and drought tolerant Hill banana (HB; AAB genome) to individual drought, heat and their combination under controlled and field conditions. Drought and combined drought and heat treatments caused greater reduction in leaf relative water content and greater increase in ion leakage and H2 O2 content in GN plants, especially in early stages, while the responses were more pronounced in HB at later stages. A combination of drought and heat increased the severity of responses. Real-time expression patterns of the A-1 and A-2 group DEHYDRATION-RESPONSIVE ELEMENT BINDING (DREB) genes revealed greater changes in expression in leaves of HB plants for both the individual stresses under controlled conditions compared to GN plants. A combination of heat and drought, however, activated most DREB genes in GN but surprisingly suppressed their expression in HB in controlled and field conditions. Its response seems correlated to a better stomatal control over transpiration in HB and a DREB-independent pathway for the more severe combined stresses unlike in GN. Most of the DREB genes had abscisic acid (ABA)-responsive elements in their promoters and were also activated by ABA suggesting at least partial dependence on ABA. This study provides valuable information on physiological and molecular responses of the two genotypes to individual and combined drought and heat stresses.