Hemiparasitic plants are known to be able to diversify degraded grasslands by lowering the competitive power of dominant grasses. Recent research indicates that hemiparasites may also be used against invasive alien plants. Here, we tested the effects of Odontites luteus, a native European hemiparasite, on Sporobolus cryptandrus, a recently established and rapidly spreading C4 grass of North-American origin. We found that Odontites considers Sporobolus a suitable host and reduces its biomass production (and potentially its competitive ability) by approx. 50%, equaling the effect on its major native host, Festuca vaginata. However, Festuca showed severe metabolic impairment (reduced photosynthetic capacity and increased physiological stress) under hemiparasite pressure. So, the application of hemiparasites is a promising biocontrol tool against Sporobolus (and potentially other invasive C4 grasses), but it is not a silver bullet. We cannot expect a full eradication of the invasive species and a recovery of the native community but thinning monodominant Sporobolus stands to allow certain populations of native species, particularly those resistant to Odontites, to come back is a more realistic goal. This could lead to a partial recovery of the former species composition and an improvement of ecosystem functions, such as providing food for pollinators.

Nocturnal red light application affects defence-related enzymes in wheat, in particular antioxidants and glutathione transferases (GSTs), which are crucial for successful plant defence. In our study, we sought to answer the question of whether night-time illumination during anthesis induces detectable changes in the infection responses of wheat cultivars with different levels of Fusarium resistance. To address this question, we investigated a range of factors from yield parameters and membrane status to changes in enzyme activities and gene expression and its regulation. Nocturnal red light treatment increased the activities of superoxide dismutase, catalase, guaiacol-dependent peroxidase and GSTs. In parallel with increased activity of detoxification enzymes, a higher grain yield was observed in the more resistant wheat line during infection by Fusarium graminearum. Notably, GSTs, which are typically down-regulated in darkness, were strongly up-regulated by red light at night in the more susceptible cultivar, especially TaGSTU1B and TaGSTF5. In addition, an exceptionally high and light-dependent transcriptional activity of TaGSTF5 was detected in the sensitive line. Sequence analysis of the regulatory region of TaGSTF5 identified an additional GATA box, a circadian regulatory element, which may be responsible for the increased transcript levels. These results suggest that nocturnal red light can effectively enhance antioxidant and GST activity as part of the defence of wheat against Fusarium head blight, but this depends on the Fusarium resistance of the selected wheat genotypes.

The interaction between ethylene (ET) and light/dark cycles is complex and regulates plant growth, development and stress responses. While ET synthesis is influenced by circadian rhythms, light -especially red light- it can also affect ET-regulated processes, depending on the developmental stage and organ type. This study investigated the effects of nocturnal red light exposure on mature tomato plant leaves, using wild-type (WT) and ET-insensitive Never ripe (Nr) mutant. Red light application for one week at night did not significantly affect leaf biomass and area, but it altered structural traits such as leaf thickness and internode length, particularly in WT plants. Transcriptomic analyses indicated significant differences in gene expression between WT and Nr plants, particularly in genes related to photosynthesis, growth regulation and the circadian clock. Red light also modulated the expression of hormone-related genes and increased the levels of defence-related phytohormones (ET, salicylic acid, abscisic acid) as well as the activity of antioxidant enzymes (e.g. guaiacol peroxidase, glutathione S-transferase) in a manner dependent on ET in WT plants. Interestingly, although ET is involved in many of these processes, red light was also found to increase biotic stress resistance in Nr mutants, as evidenced by reduced Botrytis cinerea infection. This suggests that red light may activate defence pathways independently of ET. Our findings highlight the potential of red light as an environmentally friendly tool for improving crop disease resistance and emphasise the pivotal role of ET signalling, which can be regulated by specific light spectra, in plant’s defence reactions.

Salt stress is one of the critical global issues significantly lowering crop yield and agricultural production. As agricultural soil salt concentration keeps rising owing to natural and anthropogenic factors, plants face severe challenges such as osmotic stress, ion toxicity, and oxidative damages, which collectively inhibit growth and development. Among the myriad of plant responses to salt stress, manipulation of abscisic acid (ABA) proves to be effective and promising approach for inducing plant salt stress tolerance. The current review presents a detailed discussion on how ABA fortifiesdefense systems against oxidative damages under salt stress. Additionally, it also focuses on ABA interaction with plant growth regulators and transcription factors (TFs) to activate salt stress-responsive genes/proteins/metabolites to enhance plant salt stress resilience. This review also highlights the complex ABA-mediated regulatory networks responsible for salt tolerance, and also presents the recent progress made in functional genomics on ABA biosynthesis and signaling. By integrating existing studies, this review propounds the potentiality of ABA-targeted approaches to enhance crop tolerance in salt environments for sustainable agriculture.

Photosynthesis is one of the main processes affected by salinity. Salt stress limits the availability of CO2 by restricting its diffusion through stomata; leads to chlorophyll degradation, damage to light-harvesting complexes, suppression of PSII activity and reduced biomass production. Nitric oxide (NO) is an important signalling molecule with many physiological functions. NO can alleviate salt-induced changes in photosynthesis. However, the role of NO in the photosynthetic apparatus (especially PSI) of salt-stressed plants is poorly understood, especially at different leaf ages. Our results showed that the effect of exogenous NO donor sodium nitroprusside (SNP) application on photosynthetic performance measured by Dual-PAM and LI-COR portable photosynthesis system in tomato leaves was dependent on leaf developmental stage. After one week, 0.1 mM SNP treatments via the rooting medium significantly attenuated the decrease in photosynthetic parameters, especially in young leaves, such as leaf chlorophyll content, net photosynthetic rate, stomatal conductance, effective quantum yield of PSII and PSI, and counteracted the increase in the quantum yield of regulated non-photochemical quenching [Y(NPQ)] and cyclic electron flow [Y(CEF)]. At the same time, salt stress-induced deleterious effects were the most pronounced in old leaves based on changes in biomass, maximum PSII quantum yield (Fv/Fm), photosynthetic pigment loss and lipid peroxidation, which were only partially alleviated by SNP. The results showed that exogenous application of SNP improved photosynthetic performance in salt-stressed tomato plants in a leaf level-dependent manner and was the most effective in young, developing leaves, which was associated with an increase in PSII and PSI efficiency.

The global rise in resistance to chemical fungicides and their strict regulation by the EU, has created an urgent need for alternative antifungal strategies in agriculture. Plant defensins represent promising alternatives owing to their broad-spectrum antifungal activity, structural stability, and low toxicity to mammalian cells and plants. In this study, we identified and characterized a novel antifungal defensin, K4CBP6, from Solanum lycopersicum L., along with its γ-core peptide derivatives, K4CBP6γ1 and K4CBP6γ2, as potential biofungicide agents. Protein database mining revealed a widespread distribution of K4CBP6 homologs within the Solanaceae family. Recombinant K4CBP6 (rK4CBP6) was successfully produced using a Komagataella phaffii-based expression system, while K4CBP6γ1 and K4CBP6γ2 were chemically synthesized. Structural analyses via electrospray ionization mass spectrometry and electronic circular dichroism spectroscopy confirmed a cysteine-stabilized α-helix β-strand folded structure for rK4CBP6. In vitro susceptibility assays demonstrated that both rK4CBP6 and K4CBP6γ2 exhibited antifungal activity against major tomato pathogens, Botrytis cinerea, Cladosporium herbarum, and Fusarium oxysporum with minimum inhibitory concentrations ranging from 12.5 to 25 µg ml-1. Furthermore, neither rK4CBP6 nor K4CBP6γ2 exhibited cytotoxic effects on mammalian cell lines or adverse effects in animal and plant model systems even at concentrations of 200 and 400 µg ml-1. Proof-of-concept experiments on tomato plants and fruits confirmed their protective efficacy against B. cinerea and C. herbarum. These findings highlight the potential of rK4CBP6 and K4CBP6γ2 as sustainable biofungicide candidates for plant disease management, owing to their antifungal efficacy both in vitro and in planta, along with their lack of cytotoxic effects.

Bacterial flagellin (flg22) induces rapid and permanent stomatal closure. However, its local and systemic as well as tissue- and cell-specific effects are less understood. Our results show that flg22 induced local and systemic stomatal closure in intact tomato plants, which was regulated by reactive oxygen- and nitrogen species, and also affected the photosynthetic activity of guard cells but not of mesophyll cells. Interestingly, rapid and extensive local expression of Ethylene response factor 1 was observed after exposure to flg22, whereas the relative transcript levels of Defensin increased only after six hours, especially in systemic leaves. Following local and systemic ethylene emission already after one and six hours, jasmonic acid levels increased in the local leaves after six hours of flg22 treatment. Using immunohistochemical methods, significant defensin accumulation was found in the epidermis and stomata of flg22-treated leaves and above them. Immunogold labelling revealed significant levels of defensins in the cell wall of the mesophyll parenchyma and guard cells. Furthermore, single cell qRT-PCR confirmed that guard cells are able to synthesise defensins. It can be concluded that guard cells are not only involved in the first line of plant defense by regulating stomatal pore size, but can also defend themselves and the plant by producing and accumulating antimicrobial defensins where phytopathogens can penetrate.

Alpha-tocopherol (α-tocopherol), a major member of the tocochromanol family, plays a crucial role in scavenging reactive oxygen species generated during photosynthesis. Recent studies have revealed additional roles of α-tocopherol in metabolic processes, development, and stress responses, indicating its complex interaction with plant phytohormones. However, the metabolism and hormonal regulation of α-tocopherol under normal or stressful conditions has not been thoroughly investigated. Furthermore, the molecular and biochemical regulation of α-tocopherol in different plant organs in response to biotic or abiotic stress, and its hormonal regulation, have received less attention. The aim of this review is to assess and summarize the existing literature in order to better understand the biosynthesis and role of α-tocopherol mediated by phytohormones. Based on these data, the amount of α-tocopherol changes not only in photosynthesising leaves, but also during fruit ripening and in roots, seed development and germination (in the dark), which is influenced by many hormones such as auxin, cytokinins, abscisic acid and ethylene. In addition, the levels of defense hormones such as salicylic acid, ethylene or abscisic acid are higher in several vte mutants, further demonstrating the close relationship between the regulation of tocopherol metabolism and phytohormones. These interactions have the potential to influence key biological processes such as growth, development and various stress responses. By summarising current knowledge, this review highlights the multiple roles of α-tocopherol and provides evidence linking α-tocopherol metabolism and phytohormone signaling. Understanding these interactions may provide alternative ways to enhance plant defense responses and productivity through biotechnology and agricultural practices.

This study explores the long-term effects of nocturnal red light treatment on tomato plants, focusing on photosynthesis, metabolism, and defence mechanisms. The impact of red light treatment applied at night to both young and old leaves at various times of day was investigated. The results showed that, after three weeks, nocturnal red light treatment improved photosynthetic efficiency in both upper and lower leaves, particularly in the morning and at noon. This enhancement in photosynthesis was associated with higher CO2 assimilation. Interestingly, older leaves, which usually demonstrate reduced photosynthetic activity, also benefited from red light exposure. Additionally, red light treatment resulted in significant changes to the accumulation of starch and sugars. Higher levels of starch were found in the leaves in the afternoon, alongside increased levels of sucrose in both leaves. Metabolomics analysis revealed that the level of several defence-related metabolites, including 4-guanidinobutyric acid, fucose and quinic acid, increased following exposure to red light. This suggests that red light applied at night could have a priming effect, enhancing defence against pathogens. Conversely, the levels of some metabolites, such as myo-inositol and N-acetylaspartate, decreased, indicating adjustments in plant stress responses. Red light influenced plant height and leaf area and enhanced callose content in older leaves. Moreover, red light can hard plants against fungal pathogens, such as Botrytis cinerea. These results suggest that exposure to red light at night is an effective, environmentally friendly approach to enhance the resilience of tomato plants and optimise greenhouse farming practices, particularly through supplemental or interlighting systems.

Fusarium pathogens are causal agents of several crop diseases and produce harmful mycotoxins resulting in crop and yield reduction worldwide. Among crop diseases, Fusarium wilt, Fusarium head blight, and Fusarium root blight are mostly reported diseases in numerous vegetables, crops, and fruits and have posed pressure on current food production and safety. In addition, the production of mycotoxins further aggravates plant health and causes serious health risks in humans and animals through food chain contamination. Different management practices have been enlisted in this chapter to reduce or eradicate Fusarium wilt in different crops. Interestingly, various mechanisms developed by plants have also been highlighted to fight against Fusarium pathogens and limit the growth of mycotoxins. One of defence mechanisms is plant antioxidant mechanisms to reduce oxidative stress by increasing enzymatic and non-enzymatic antioxidants to maintain cellular homeostasis under Fusarium infection. The other defence response is through hormonal signalling to combat fungal pathogens. Different phytohormones such as salicylic acid, ethylene, jasmonate, abscisic acid, cytokinin, auxin, and other plant secondary metabolites play a crucial part in the reduction of Fusarium growth and inhibit mycotoxin production through defence-related genes. Further, the use of different pre-harvest and post-harvest strategies has been elucidated to enhance plant resistance and growth by decreasing fungal pathogenicity and virulence.

Plant infections caused by fungi lead to significant crop losses worldwide every year. This study aims to better understand the plant defence mechanisms regulated by red light, in particular, the effects of red light at night when most phytopathogens are highly infectious. Our results showed that superoxide production significantly increased immediately after red light exposure and, together with hydrogen peroxide levels, was highest at dawn after 30 min of nocturnal red-light treatment. In parallel, red-light-induced expression and increased the activities of several antioxidant enzymes. The nocturnal red light did not affect salicylic acid but increased jasmonic acid levels immediately after illumination, whereas abscisic acid levels increased 3 h after nocturnal red-light exposure at dawn. Based on the RNAseq data, red light immediately increased the transcription of several chloroplastic chlorophyll a-b binding protein and circadian rhythm-related genes, such as Constans 1, CONSTANS interacting protein 1 and zinc finger protein CONSTANS-LIKE 10. In addition, the levels of several transcription factors were also increased after red light exposure, such as the DOF zinc finger protein and a MYB transcription factor involved in the regulation of circadian rhythms and defence responses in tomato. In addition to identifying these key transcription factors in tomato, the application of red light at night for one week not only reactivated key antioxidant enzymes at the gene and enzyme activity level at dawn but also contributed to a more efficient and successful defence against Botrytis cinerea infection.

Plant hormones such as ethylene (ET) and salicylic acid (SA) have an elementary role in the regulation of ER stress and unfolded protein response (UPR) in plants via modulating defence responses or inducing oxidative stress. Chloroplasts can be sources and targets of reactive oxygen species (ROS) that affect photosynthetic efficiency, which has not been investigated under tunicamycin (Tm)-induced ER stress. In this study, the direct and indirect effects of Tm on chloroplastic ROS production were first investigated in leaves of wild-type tomato (Solanum lycopersicum L.) plants. Secondly changes in activities of photosystem II and I were analysed under Tm exposure and after application of the chemical chaperone 4-phenylbutyrate (PBA) in different genotypes, focusing on the regulatory role of SA and ET Tm treatments significantly but indirectly induced ROS production in tomato leaves and in parallel it decreased the effective quantum yield of PSII [Y(II)] and PSI [Y(I)], as well as the photochemical quenching coefficient (qP) and the quantum yield of non-photochemical energy dissipation in PSI due to acceptor-side limitation [Y(NA)]. At the same time, Tm increased non-photochemical quenching (NPQ) and cyclic electron flow (CEF) in tomato leaves after 24 h. However, the photosynthetic activity of the SA hydroxylase-overexpressing NahG tomato plants was more severely affected by Tm as compared to wild-type and ET-insensitive Never ripe (Nr) plants. These results suggest the protective role of SA in the regulation of photosynthetic activity contributing to UPR and the survival of plants under ER stress. Interestingly, the activation of photoprotective mechanisms by NPQ was independent of SA but dependent on active ET signalling under ER stress, whereas CEF was reduced by ET due to its higher ratio in Nr plants.

Agricultural sufficient productivity is of paramount importance for ensuring food security and conserving soil health to support the world's agronomy. Climatic abruptions have been emerging as one of the most nerve-pressing issues for the sustainment of the planet Earth in the twenty-first century. Among the various environmental constraints, drought stress stands out as a potent factor restricting crop growth and productivity. It triggers a myriad of intricate responses in plants to combat the underlying stress-mediated adversities. Gaining a comprehensive understanding of the key physiological and molecular mechanisms that enable plants to withstand drought stress is crucial for developing effective strategies to enhance crop resilience. Ethylene, a gaseous plant hormone, influences the adaptive measures adopted by plants subjected to drought stress by regulating the drought stress-mediated signal transduction-associated responses. The present review article provides an in-depth understanding of the critical roles of ethylene in enhancing plants' ability to restrain the severity of drought stress. It also highlights the significance of ethylene signaling components in regulating plant survival and drought stress tolerance. Additionally, we have illustrated the additive and antagonistic interactions of ethylene with other plant growth regulators, which instigate the tolerance responses. Conclusively, this review emphasizes the significance of complex networks involved in ethylene-mediated drought tolerance, providing valuable insights for future research and uncovering novel studies in the field of ethylene biology.

Plants produce a wide variety of secondary metabolites to sustain and protect themselves against a wide range of stresses. Among these metabolites, tannins are one of the most abundant polyphenolic compounds, accounting for 25% of the dry weight of leaves, roots and bark of woody plants, but are also abundant in flowering and seed-producing plants. The presence of tannins in these organs serves to protect plants against herbivorous and pathogenic attack through their antidigestive and antimicrobial properties. In addition, tannins play a role in regulating plant growth and development by inhibiting the consumption of unripe fruits due to their astringency. In addition, several studies have also revealed various roles of them under environmental stresses. Tannins can be classified into condensed tannins (CTs), hydrolysable tannins (HTs) and phlorotannins. They are synthesised in plants via the acetate–malonate and shikimic acid pathways. Their accumulation is regulated by several transcription factors during normal development and under different stress conditions. Despite their multiple roles in plant life, information on the regulation of tannin metabolism by defence-related phytohormones is very limited. To cope with biotic and abiotic stresses, plant responses are regulated by defence-related phytohormones such as salicylic acid (SA), jasmonic acid (JA), ethylene (ET) and abscisic acid (ABA), which act as regulators of tannin production under adverse conditions. This review focuses on tannin production, moreover its occurrence, defence potential and regulation by phytohormones under different environmental and biotic stresses, based on the most recent and relevant data. Graphical Abstract

Plants have to change their metabolism constantly by fluctuations in environmental conditions and stress effects. These processes are mediated by the key defense-related phytohormones, such as salicylic acid, jasmonic acid, and ethylene. These phytohormones play a crucial role in the regulation of various stress responses in physiological, biochemical, and molecular levels. Polyamines (PAs) are important participants in the stress tolerance mechanism in crops, but their metabolism is regulated in a complex manner. In this chapter, we would like to summarize the current knowledge about the mode of action of these phytohormones on PA metabolism in different plant species, genotypes or organs of crops. Moreover, effects of exogenous PAs application were discussed on defense-related phytohormone biosynthesis and signaling in crops. Understanding the role of phytohormones on PA metabolism and vice versa can help to increase our ability to improve stress resistance in crops in the future.

Plants are exposed to various biotic stressors during their life which often leads to a localized cell death termed as hypersensitive response (HR) and induces systemic responses in their distal organs from the infected ones which often promotes the development of systemic acquired resistance (SAR) against secondary pathogen infection. These processes are regulated by various phytohormones, defense-related molecules, and free radicals such as reactive oxygen species (ROS) and nitric oxide (NO). NO acts together with these compounds regulating HR and rapid systemic defense responses of plants such as SAR, as well as taking part in the induced systemic resistance (ISR). In this chapter, the production and transport of NO and its signaling functions are summarized and shown in the acquired- or induced-, rapid- and long-term systemic responses of plants.

Plant defence responses induced by the bacterial elicitor flg22 are highly dependent on phytohormones, including gaseous ethylene (ET). While the regulatory role of ET in local defence responses to flg22 exposure has been demonstrated, its contribution to the induction of systemic responses is not clearly understood. For this consideration, we examined the effects of different ET modulators on the flg22-induced local and systemic defence progression. In our experiments, ET biosynthesis inhibitor aminoethoxyvinyl glycine (AVG) or ET receptor blocker silver thiosulphate (STS) were applied 1 h before flg22 treatments and 1 h later the rapid local and systemic responses were detected in the leaves of intact tomato plants (Solanum lycopersicum L.). Based on our results, AVG not only diminished the flg22-induced ET accumulation locally, but also in the younger leaves confirming the role of ET in the whole-plant expanding defence progression. This increase in ET emission was accompanied by increased local expression of SlACO1, which was reduced by AVG and STS. Local ET biosynthesis upon flg22 treatment was shown to positively regulate local and systemic superoxide (O2.-) and hydrogen peroxide (H2O2) production, which in turn could contribute to ET accumulation in younger leaves. Confirming the role of ET in flg22-induced rapid defence responses, application of AVG reduced local and systemic ET, O2.and H2O2 production, whereas STS reduced it primarily in the younger leaves. Interestingly, in addition to flg22, AVG and STS induced stomatal closure alone at whole-plant level, however in the case of combined treatments together with flg22 both ET modulators reduced the rate of stomatal closure in the older- and younger leaves as well. These results demonstrate that both local and systemic ET production in sufficient amounts and active ET signalling are essential for the development of flg22-induced rapid local and systemic defence responses.