Physiological and hormonal responses underlying salinity tolerance in wild tomatoes: Insights for cultivated varieties

Physiological responses to Megafol® treatments in tomato plants under drought stress: A phenomic and molecular approach

Tomato (Lycoperiscon esculentum) and rice (Oryza sativa) are the two most important agricultural crops whose productivity is severely impacted by salinity stress. Soil salinity causes an irreversible damage to the photosynthetic apparatus in plants at all developmental stages leading to significant reduction in agricultural productivity. Reduction in photosynthesis is the primary response that is observed in all glycophytic plants during salt stress. Employment of salt-tolerant plant growth-promoting bacteria (PGPB) is an economical and viable approach for the remediation of saline soils and improvement of plant growth. The current study is aimed towards investigating the growth patterns and photosynthetic responses of rice and tomato plants upon inoculation with halotolerant PGPB Staphylococcus sciuri ET101 under salt stress conditions. Tomato and rice plants inoculated with PGPB showed increased growth rate and stimulated root growth, along with higher transpiration rates (E), stomatal conductance (gs), and intracellular CO2 accumulation (Ci). Additionally, correlation of relative water content (RWC) to electrolyte leakage (EL) in tomato and rice plants showed decreased EL in inoculated plants during salt stress conditions, along with higher proline and glycine betaine content. Energy dissipation by non-photochemical quenching (NPQ) and increased photorespiration of 179.47% in tomato and 264.14% in rice plants were observed in uninoculated plants subjected to salinity stress. Furthermore, reduced photorespiration with improved salinity tolerance is observed in inoculated plants. The higher rates of photosynthesis in inoculated plants during salt stress were accompanied by increased quantum efficiency (ΦPSII) and maximum quantum yield (Fv/Fm) of photosystem II. Furthermore, inoculated plants showed increased carboxylation efficiency of RuBisCO, along with higher photosynthetic electron transport rate (ETR) (J) during salinity stress. Although the total cellular ATP levels are drastically affected by salt stress in tomato and rice plants along with increased reactive oxygen species (ROS) accumulation, the restoration of cellular ATP levels in leaves of inoculated plants along with decreased ROS accumulation suggests the protective role of PGPB. Our results reveal the beneficial role of S. sciuri ET101 in protection of photosynthesis and amelioration of salinity stress responses in rice and tomato plants.

Phytopathogen attacks threaten plant biodiversity and food production worldwide and are expected to worsen due to climate change. To reduce agricultural dependence on synthetic pesticides, eco-friendly alternatives must be developed. We have recently shown that aqueous extracts from dried leaves of young Eucalyptus globulus Labill. had promising in vitro antibacterial activity against phytopathogens. However, its in vivo effectiveness remains unclear. Thus, this study aimed to evaluate the efficacy of the extract against tomato seeds and plants infected with Xanthomonas euvesicatoria (Jones et al.) Constantin et al. (Xeu), as well as to assess the plant's physiological responses upon biopesticide application. For this, Solanum lycopersicum L. cv. Roma seeds were inoculated with a Xeu suspension, incubated with the extract (0, 15, and 30 g L-1), and left for germination for 10 days. The treatment of inoculated seeds with the extract increased radicle length and reduced the incidence of symptomatic cotyledons. Parallely, 1-month-old tomato plants were foliar-infected with a Xeu suspension and treated with various concentrations of the extract. Disease symptoms were monitored weekly over 3 weeks, showing a dose-dependent decrease following extract application. After 21 days, the extract at both concentrations equally reduced the leaf bacterial population compared to infected plants. The application of the extract at 15 g L-1 to infected plants improved their physiological status by enhancing antioxidant enzyme activity and photosynthetic performance. Overall, these findings suggest that the extract can be used as an effective tool against Xeu and contribute to reducing pesticide application. © 2025 Society of Chemical Industry.

Although the effects of high-frequency electromagnetic fields on biological systems have been studied frequently, unequivocal results have rarely been obtained, primarily because suitably controlled experiments could not be performed. In the present work, tomato plants were exposed to a homogeneous and isotropic field (900 MHz) using a mode stirred reverberation chamber, and the stress-related transcripts (calmodulin, protease inhibitor and chloroplast mRNA-binding protein) were assayed by real-time quantitative PCR. Exposure to an electromagnetic field induced a biphasic response, in which the levels of all three transcripts increased four-to six-fold 15 min after the end of electromagnetic stimulation, dropped to close to initial levels by 30 min, and then increased again at 60 min. We deliberately focused on the very early molecular responses to high-frequency electromagnetic fields in order to minimize secondary effects.

Effects of uncoated and citric acid coated cerium oxide nanoparticles, bulk cerium oxide, cerium acetate, and citric acid on tomato plants

Enhancing atmospheric CO2 levels in commercial glasshouses is a widely used technique to increase productivity, but has high-energy costs and detrimental environmental impacts due to frequent ventilation of the glasshouse (to prevent plant diseases) releasing CO2 into the atmosphere. Previous studies suggest that enrichment of the root zone (RZ) with CO2 (RZ CO2) may be a more economic and sustainable alternative to aerial CO2 enrichment. This thesis aimed to compare the effects of RZ dissolved inorganic carbon (DIC) enrichment by adding either bicarbonate (HCO3-) or gaseous CO2 to hydroponic and aeroponic systems, and to determine the physiological and molecular mechanisms by which plants respond to RZ DIC. Supplying hydroponically grown plants with high bicarbonate concentrations (20 mM) inhibited growth of lettuce, pepper and tomato. However, lower concentrations increased biomass accumulation in lettuce (10% increase at both 1 mM and 5 mM HCO3-) and pepper (10% increase at 1 mM HCO3-), but had no effect in tomato. Exposing plants to 1 mM NaH13CO3- significantly increased shoot δ13C values over time, therefore confirming the uptake of DIC by the roots. Root δ13C values also significantly increased over time, however higher values at the beginning of NaH13CO3- exposure suggested root-to-shoot transport of DIC. Nutrient solution pH did not affect root carbon uptake, but shoot δ13C values were lower in those plants exposed to lower pH levels (5.8) compared to those exposed to fluctuating pH (between 6.3 and 6.7), suggesting differences in root-to-shoot transport of DIC. Thus, root carbon uptake was independent of the form in which CO2 was provided (gaseous CO2 at pH 5.8; HCO3- at higher pHs). Adding 1 mM HCO3- to hydroponically grown plants did not change foliar nutrient content, but K, P, N, Zn, Cu and Mn concentrations decreased at 20 mM HCO3-, suggesting nutrient deficiencies could limit growth. Applying 2000 ppm RZ CO2 to hydroponically grown lettuce, tomato and pepper did not affect biomass accumulation. Applying 1500 ppm CO2 to the RZ of aeroponically grown lettuce increased shoot biomass between 19-25% (in 4 independent experiments) compared to those grown with 400 ppm RZ CO2. However, leaf gas exchange measurements were inconsistent and therefore increased biomass could not be attributed to higher photosynthetic rates. In another 3 independent experiments, applying 1500 ppm CO2 to the RZ of aeroponically grown lettuce did not stimulate biomass accumulation, probably because the plants were exposed to higher night temperatures. Similarly, pepper and tomato did not show any biomass response to elevated RZ CO2, suggesting that the responses to RZ CO2 concentration are environment- and species-dependent. Nutrient analysis indicated that aeration with high RZ CO2 decreased lettuce foliar Mg and S concentrations, whereas root N concentrations were higher than control plants. Multi-hormone analysis of foliar and root tissues revealed that lettuce plants showed few differences in hormone status following RZ CO2 enrichment. High RZ CO2 increased foliar jasmonic acid concentration of lettuce, but the physiological significance of this change is not clear. Pepper plants showed significantly higher foliar 1-aminocyclopropane-1-carboxylic acid and lower trans-zeatin and salicylic acid concentrations, as well as lower root N6-(Δ2-isopentenyl) adenine and higher salicylic acid and gibberellic acid concentrations. These hormonal responses were associated with lower leaf area expansion of pepper plants exposed to elevated RZ CO2. Finally, transcriptome analysis of lettuce plants indicated that fatty acid biosynthesis, amino acid biosynthesis and carbon metabolism appeared to be the major pathways enriched in roots exposed to elevated RZ CO2. In addition, proteins related to the cell walls and membranes seemed enhanced under elevated RZ CO2. Although increased CO2 concentration around the roots caused major transcriptomic restructuring, the aerial parts of the plants showed limited transcriptomic changes. Taken together, this thesis is the first study of the responses of several horticultural species to elevated RZ CO2 within different growing systems in order to decipher the impact that elevated RZ CO2 has on crop productivity. Although bicarbonate enrichment of hydroponics and RZ CO2 enrichment of aeroponics stimulated biomass accumulation of lettuce in many experiments, further work is required to fully understand the physiological response mechanisms to RZ CO2. Whether the root transcriptomic changes in response to elevated RZ CO2 represent an adaptive response to their environment requires a better temporal understanding of changes in specific genes. Ultimately, whether these changes are functionally significant to shoot growth seems to be strongly environmentally regulated.

The aim of the present study was to investigate the physiological responses of six tomato (Lycopersicon esculentum Mill .) cultivars to water stress. To this end, plants were exposed to slow dehydration at the third unfolded leaf stage for 23 days. The relative water content (RWC), leaf area and leaf L-proline were determined at 10, 17 and 23 days after treatment application. Our results showed that during slow dehydration, the leaf RWC declined in all studied genotypes, whereas L–proline accumulated. A statistically significant effect of the sampling date (water stress duration) on RWC values was also observed. In addition, the differences in proline content were significantly influenced by tomato genotype, sampling date and the level of substrate saturation. Putting all these together, the results of this study indicate that the adaptive potential of the studied genotypes was expressed in a different relationship between the relative water content and growth of the leaf area. However, three of the tomato genotypes exhibited reduced growth in leaf area in response to the decreased RWC, whereas other tomato genotypes retained a balanced RWC accompanied by further growth of the leaf area.

Bacillus spizizenii is for the first time described as a plant growth salt-tolerant bacterium able to alleviate salt stress in crop plants by improving physiological parameters and antioxidant defense mechanisms. Agricultural soil salinization is a serious issue worldwide affecting agricultural yield. Plant growth promoting bacteria can enhance salt tolerance and plant yield. Bacillus spizizenii FMH45 has been shown to inhibit fungal attacks in tomato fruits and to augment tomato seed germination in presence of abiotic stresses. During this study, we reported for the first time B. spizizenii as a salt-tolerant bacterium able to alleviate salt stress in tomato plants. B. spizizenii FMH45 was examined in vitro for its potential to produce several plant growth promoting characters (siderophores, IAA, and phosphate solubilization) and hydrolytic enzymes (cellulase, glucanase and protease) in the presence of saline conditions. FMH45 was also investigated in vivo in pot experiments to evaluate its ability to promote tomato plant growth under salt stress condition. FMH45 inoculation, enhanced tomato seedling length, vigor index, and plant fresh and dry weights when compared to the non-inoculated controls exposed and not exposed to a regular irrigation with salt solutions containing: 0; 3.5; 7; and 10g L-1 of NaCl. FMH45-treated plants also presented improved chlorophyll content, membrane integrity (MI), and phenol peroxidase (POX) concentrations, as well as reduced malondialdehyde (MDA) and hydrogen peroxide (H2O2) levels under saline conditions with a significant salinity × strain interaction. Furthermore, FMH45 inoculation significantly decreased endogenous Na+ accumulation, increased K+ and Ca2+ uptake, and thereby improved K+/Na+ and Ca2+/Na+ ratios. This study proves that bio-inoculation of FMH45 efficiently increases salt tolerance in tomato plants. This sustainable approach can be applied to other stressed plant species in affected soils.

Water stress is a major limiting factor in agriculture, particularly in the Mediterranean region, where climate change exacerbates drought conditions. Soil microbiome composition plays a crucial role in plant resilience to environmental stressors, particularly water scarcity and excess. This study examines the impact of different irrigation regimes (optimal, severe deficit, and excess) on tomato soil microbiome composition and plant physiology in a Mediterranean context. Metataxonomic profiling revealed significant shifts in microbial community structure: Proteobacteria dominated under optimal irrigation (WO), Acidobacteria under water deficit (WD), and Actinobacteria under both water deficit and excess (WE). Functional analysis indicated irrigation-induced alterations in microbial metabolic pathways, influencing nutrient cycling. Soil respiration varied, peaking in the WE condition. Plant physiological responses, including gas exchange and Proline content, were significantly affected by water stress. An inverse correlation was observed between microbial diversity and chlorophyll content, suggesting a link between plant stress responses and soil microbial composition. This study underscores for the first time the intricate relationship between water availability and microbial community dynamics, emphasizing the importance of microbiome-driven soil and plant resilience, thus showing this be a key factor in agricultural sustainability under changing climatic conditions.

Soil compaction occurs when external pressures (from heavy machinery or grazing animals) exerted on the soil surface increase soil bulk density, reducing porosity and aggregation. Nutrient, air and water holding capacities of the soil are reduced, and plant roots encounter increased mechanical resistance as they grow. Soil compaction also stunts shoot growth, with hydraulic and chemical signalling systems between below- and above-ground parts allowing the plant to adapt to this multi-stress environment. However, relatively few studies have characterised root-to-shoot signalling systems of plants with mechanically-impeded roots. Tomato plants (Solanum lycopersicum cv. Ailsa Craig) were grown under low and high soil bulk densities, and allowed to dry the soil to investigate plant physiological responses. Compact soil stunted plant growth, decreased stomatal conductance of well-watered plants and decreased plant water status at higher soil water contents. Multi-hormone analyses of root xylem sap and foliar tissues revealed that high bulk density soils attenuated the soil drying-induced increase in xylem [ABA]. Moreover, high bulk density soil increased xylem jasmonic acid concentrations and decreased foliar bioactive gibberellins, which were correlated with reduced shoot growth. Root drenches of bioactive gibberellic acid (GA3) were then applied to determine its ability to improve tomato shoot growth in compact soil. GA3 was transported from root to shoot tissues and significantly increased leaf expansion, but at the expense of plant water status. Further multi-hormone analyses indicated that GA3 application increased foliar cytokinin (trans-Zeatin) levels and decreased xylem jasmonic acid concentrations. Finally, to isolate soil strength from possible confounding effects of nutrient and water availability, tomato plants were grown in a sand culture system. A light foam block or 17 kg weight was placed upon the surface of the sand to increase substrate strength, while tanks were supplied with ample nutrients and water by capillary action. While GA3 again rescued shoot growth, shoot and leaf water potentials were reduced. Furthermore, xylem jasmonic acid concentration consistently decreased in both sand- and soil-grown plants as soil strength increased, which was not attributed to any decrease in leaf water status. Taken together, this thesis is the first to employ multi-hormone analyses on tissues and sap from plants growing in compact or strong soils. Novel roles for gibberellins and jasmonic acid in regulating plant growth when roots are mechanically impeded were discovered. GA3 appears to promote shoot growth against water potential gradients. Further study of the physiological significance of xylem-transported jasmonic acid and its cross-talk with gibberellins seem necessary to help determine how plants respond to soil mechanical stresses.

Trichoderma parareesei and Trichoderma reesei (teleomorph Hypocrea jecorina) produce cellulases and xylanases of industrial interest. Here, the anamorphic strain T6 (formerly T. reesei) has been identified as T. parareesei, showing biocontrol potential against fungal and oomycete phytopathogens and enhanced hyphal growth in the presence of tomato exudates or plant cell wall polymers in in vitro assays. A Trichoderma microarray was used to examine the transcriptomic changes in T6 at 20 h of interaction with tomato plants. Out of a total 34,138 Trichoderma probe sets deposited on the microarray, 250 showed a significant change of at least 2-fold in expression in the presence of tomato plants, with most of them being downregulated. T. parareesei T6 exerted beneficial effects on tomato plants in terms of seedling lateral root development, and in adult plants it improved defense against Botrytis cinerea and growth promotion under salt stress. Time course expression patterns (0 to 6 days) observed for defense-related genes suggest that T6 was able to prime defense responses in the tomato plants against biotic and abiotic stresses. Such responses undulated, with a maximum upregulation of the jasmonic acid (JA)/ethylene (ET)-related LOX1 and EIN2 genes and the salt tolerance SOS1 gene at 24 h and that of the salicylic acid (SA)-related PR-1 gene at 48 h after T6 inoculation. Our study demonstrates that the T. parareesei T6-tomato interaction is beneficial to both partners.

Pre-sowing seed priming is one of the methods used to improve the performance of tomato plants under salt stress, but its effect photosynthesis, yield, and quality have not yet been well investigated. This experiment aimed to alleviate the impact of sodium chloride stress on the photosynthesis parameters of tomato cv. Micro-Tom (a dwarf Solanum lycopersicum L.) plants exposed to salt stress conditions. Each treatment combination consisted of five different sodium chloride concentrations (0 mM, 50 mM, 100 mM, 150 mM, and 200 mM) and four priming treatments (0 MPa, -0.4 MPa, -0.8 MPa, and -1.2 MPa), with five replications. Microtome seeds were subjected to polyethylene glycol (PEG6000) treatments for 48 hours for priming, followed by germination on a moist filter paper, and then transferred to the germination bed after 24 h. Subsequently, the seedlings were transplanted into the Rockwool, and the salinity treatments were administered after a month. In our study salinity significantly affected tomato plants' physiological and antioxidant attributes. Primed seeds produced plants that exhibited relatively better photosynthetic activity than those grown from unprimed seeds. Our findings indicated that priming doses of -0.8 MPa and -1.2 MPa were the most effective at stimulating tomato plant photosynthesis, and biochemical contents under salinity-related conditions. Moreover, primed plants demonstrated relatively superior fruit quality features such as fruit color, fruit Brix, sugars (glucose, fructose, and sucrose), organic acids, and vitamin C contents under salt stress, compared to non-primed plants. Furthermore, priming treatments significantly decreased the malondialdehyde, proline, and hydrogen peroxide content in plant leaves. Our results suggest that seed priming may be a long-term method for improving crop productivity and quality in challenging environments by enhancing the growth, physiological responses, and fruit quality attributes of Micro-Tom tomato plants under salt stress conditions.

Heat and flooding are environmental stresses that inhibit tomato growth and productivity during the hot season in Taiwan. Selecting plant lines tolerant to flooding and heat would increase the productivity of tomato during the hot season. Two-month-old plants from the tomato lines Solanum pimpinellifolium L4422, S. habrochaites L3683, S. peruvianum L1947, and the tomato (S. lycopersicum L.) 'ASVEG #6' were flooded for 5 d during the hot season in Taipei. The relative water content, stomatal conductance, and chlorophyll fluorescence in the leaves, and the antioxidant contents, and activity of antioxidative and fermentative enzymes in the roots were measured. At 12 h after flooding, L1947 revealed a rapid decrease in stomatal conductance and Fm value, higher α-tocopherol content and Fv/Fm value than L4422, and higher alcohol dehydrogenase activity than that in the other three Solanum plants. The Fm values for L1947 and L3683 decreased earlier (at 12 h) than 'ASVEG #6' and L4422 (at 24 h) after flooding. The ascorbate peroxidase activity and fresh weight in L1947 root were increased at 48 h after flooding. Thus, among the four Solanum plants studied, L1947 is more tolerant to flooding during the hot season in Taipei.

Intercropping salt-sensitive Solanum lycopersicum L. and salt-tolerant Arthrocaulon macrostachyum in salt-affected agricultural soil under open field conditions: Physiological, hormonal, metabolic and agronomic responses

Global climate change will modify plants in terms of growth and physiology. To better understand the consequences of this effect, the responses of the leaf water relations and nitrogen (N) use efficiency of barley and tomato plants to elevated CO2 (e[CO2], 800 ppm) combined with progressive drought stress at two levels of N supply (N1, 0.5 g N pot−1 and N2, 1.0 g N pot−1) were studied. The plants were grown in two separate phytotrons at ambient CO2 (a[CO2], 400 ppm) and e[CO2], respectively. The leaf physiological parameters as well as carbon (C) and N concentrations were determined; plant growth, water and N use efficiencies were evaluated. The results showed that e[CO2] increased photosynthesis and water use efficiency (WUE) while decreased specific leaf area (SLA) in both species, whereas N supply level differentially influenced WUE in barley and tomato plants. The abscisic acid (ABA)-induced stomatal closure during progressive soil drying varied between the two species where the stomatal conductance (gs) of barley plants was more sensitive to leaf ABA than tomato plants, though CO2 environment did not affect the response in both species. Compared to a[CO2], e[CO2] reduced plant transpiration rate (Tplant) in barley but not in tomato. e[CO2] increased the leaf C:N ratio ([C:N]leaf) in plants by enhancing leaf C concentration ([C]leaf) in barley and by dilution of leaf N concentration ([N]leaf) in tomato, respectively, but N2 substantially decreased [C:N]leaf, and thus, N treatment was the dominant factor controlling [C:N]leaf. Collectively, appropriate N supply may modulate the acclimation of plants to e[CO2] and soil water deficits. This study provides some novel insights into N management of different plant species for adapting to future drier and CO2-enriched environment.