Unravelling the biostimulant activity of a protein hydrolysate in lettuce plants under optimal and low N availability: a multi-omics approach.

The application of protein hydrolysates (PH) biostimulants is considered a promising approach to promote crop growth and resilience against abiotic stresses. Nevertheless, PHs bioactivity depends on both the raw material used for their preparation and the molecular fraction applied. The present research aimed at investigating the molecular mechanisms triggered by applying a PH and its fractions on plants subjected to nitrogen limitations. To this objective, an integrated transcriptomic-metabolomic approach was used to assess lettuce plants grown under different nitrogen levels and treated with either the commercial PH Vegamin® or its molecular fractions PH1(>10 kDa), PH2 (1-10 kDa) and PH3 (<1 kDa). Regardless of nitrogen provision, biostimulant application enhanced lettuce biomass, likely through a hormone-like activity. This was confirmed by the modulation of genes involved in auxin and cytokinin synthesis, mirrored by an increase in the metabolic levels of these hormones. Consistently, PH and PH3 upregulated genes involved in cell wall growth and plasticity. Furthermore, the accumulation of specific metabolites suggested the activation of a multifaceted antioxidant machinery. Notwithstanding, the modulation of stress-response transcription factors and genes involved in detoxification processes was observed. The coordinated action of these molecular entities might underpin the increased resilience of lettuce plants against nitrogen-limiting conditions. In conclusion, integrating omics techniques allowed the elucidation of mechanistic aspects underlying PH bioactivity in crops. Most importantly, the comparison of PH with its fraction PH3 showed that, except for a few peculiarities, the effects induced were equivalent, suggesting that the highest bioactivity was ascribable to the lightest molecular fraction.

Effects of vegetal protein hydrolysate application method, nitrogen level, and nitrate-to-ammonium ratio on growth and composition of hydroponic lettuce.

BACKGROUND: Vegetal-derived protein hydrolysates (PHs) have been recognized as sustainable biostimulant products due to their beneficial effects on crops. However, most studies on PHs have been conducted at a fixed ratio of nitrate-to-ammonium (NO3 -:NH4 +) without considering other N application scenarios, leading to inconsistent results among the studies. This study compared the influences of N levels (2 or 10 mM N), NO3:NH4 ratios (100:0, 75:25, 50:50, or 25:75), and PH application methods - control, foliar spray (PH-F) or root application (PH-R) - on the yield, morphology, nutrients, and nutraceutical quality of hydroponic lettuce. RESULTS: Nitrogen level, NO3:NH4 ratio, and PH application affected plant growth, morphology, and quality significantly, highlighting the importance of the interactions among these factors. Shoot growth was influenced by NO3:NH4 ratios, PH, and their interactions. Similar trends were observed in chlorophyll content. The interactions among all three factors significantly influenced root growth and morphology. Root application (PH-R) protected lettuce from yield loss caused by low NO3:NH4 ratios and from reduced antioxidant compounds caused by high N levels. Vegetal-derived protein hydrolysates improved nutrient uptake through two-way and three-way interactions although neither PH nor any interactions affected nitrate concentrations. CONCLUSION: This study demonstrated that PH interacts with N level and NO3:NH4 ratio, affecting hydroponic lettuce yield and quality. In particular, the root application of PH was the most effective method for enhancing yield (shoot fresh weight), quality (chlorophylls, carotenoids, flavonoids, and phenols), and nutrient uptake in hydroponically grown lettuce in relation to N form and level. © 2024 Society of Chemical Industry.

Plant-derived biostimulant as priming agents enhanced antioxidant and nutritive properties in brassicaceous microgreens.

BACKGROUND: Microgreens constitute dietary sources of bioactive compounds imparting numerous health benefits and enhancing sensory experience. They can be successfully cultivated in soilless systems where biostimulants can be easily integrated as seed-priming and post-germination agents improving the sustainability of a crop's final production. Compared to an untreated control, three priming agents (a commercial legume-derived protein hydrolysate (A250), a novel protein hydrolysate derived from peanut biomass (H250) and hydropriming (H2O)) were applied to Komatsuna and Mibuna seeds grown as microgreens and compared for their effects on yield parameters, mineral composition, ABTS and FRAP antioxidant capacity, carotenoid concentration and phenolic compounds. RESULTS: Significant effects of the main experimental factors and their interactions were identified on antioxidant capacity. Compared to the control and hydropriming, the highest ABTS and FRAP values were observed in Mibuna with the A250 and H250 treatments, respectively. Additionally, the H250 treatment increased the total concentrations of phenolic acid derivatives and flavonoid derivatives in Mibuna and Komatsuna, in tune with the levels of total flavonoids. Concerning mineral composition, the highest concentrations in both species were those of phosphorus and nitrate. CONCLUSION: These results highlight the potential of select plant-based biostimulants as priming agents to enhance the antioxidant capacity, nutrient content and bioactive compound content, thus further increasing their functional and nutritive quality. In the light of this, the possibility of reducing the application of fertilizers by promoting a green transition for the intensive production of microgreens could subsequently be evaluated. © 2024 Society of Chemical Industry.

Foliar applications of a Malvaceae-derived protein hydrolysate and its fractions differentially modulate yield and functional traits of tomato under optimal and suboptimal nitrogen application.

BACKGROUND: Protein hydrolysates (PHs) can enhance plant nitrogen nutrition and improve the quality of vegetables, depending on their bioactive compounds. A tomato greenhouse experiment was conducted under both optimal (14 mM) and suboptimal (2 mM) nitrogen (N-NO3) conditions. Tomatoes were treated with a new Malvaceae-derived PH (MDPH) and its molecular fractions (MDPH1, >10 kDa; MDPH2, 1-10 kDa and MDPH3, <1 kDa). RESULTS: Under optimal N conditions, the plants increased biomass and fruit yield, and showed a higher photosynthetic pigment content in leaves in comparison with suboptimal N, whereas under N-limiting conditions, an increase in dry matter, soluble solid content (SSC) and lycopene, a reduction in firmness, and changes in organic acid and phenolic compounds were observed. With 14 mM N-NO3, MDPH3 stimulated an increase in dry weight and increased yield components and lycopene in the fruit. The MDPH2 fraction also resulted in increased lycopene accumulation in fruit under 14 mM N-NO3. At a low N level, the PH fractions showed distinct effects compared with the whole MDPH and the control, with an increase in biomass for MDPH1 and MDPH2 and a higher pigment content for MDPH3. Regardless of N availability, all the fractions affected fruit quality by increasing SSC, whereas MDPH2 and MDPH3 modified organic acid content and showed a higher concentration of flavonols, lignans, and stilbenes. CONCLUSION: The molecular weight of the peptides modifies the effect of PHs on plant performance, with different behavior depending on the level of N fertilization, confirming the effectiveness of fractioning processes. © 2024 Society of Chemical Industry.

Integrated Metabolomics and Morpho-Biochemical Analyses Reveal a Better Performance of Azospirillum brasilense over Plant-Derived Biostimulants in Counteracting Salt Stress in Tomato.

Increased soil salinity is one of the main concerns in agriculture and food production, and it negatively affects plant growth and crop productivity. In order to mitigate the adverse effects of salinity stress, plant biostimulants (PBs) have been indicated as a promising approach. Indeed, these products have a beneficial effect on plants by acting on primary and secondary metabolism and by inducing the accumulation of protective molecules against oxidative stress. In this context, the present work is aimed at comparatively investigating the effects of microbial (i.e., Azospirillum brasilense) and plant-derived biostimulants in alleviating salt stress in tomato plants by adopting a multidisciplinary approach. To do so, the morphological and biochemical effects were assessed by analyzing the biomass accumulation and root characteristics, the activity of antioxidant enzymes and osmotic stress protection. Furthermore, modifications in the metabolomic profiles of both leaves and root exudates were also investigated by ultra-high performance liquid chromatography/quadrupole time-of-flight mass spectrometry (UHPLC/QTOF-MS). According to the results, biomass accumulation decreased under high salinity. However, the treatment with A. brasilense considerably improved root architecture and increased root biomass by 156% and 118% in non-saline and saline conditions, respectively. The antioxidant enzymes and proline production were enhanced in salinity stress at different levels according to the biostimulant applied. Moreover, the metabolomic analyses pointed out a wide set of processes being affected by salinity and biostimulant interactions. Crucial compounds belonging to secondary metabolism (phenylpropanoids, alkaloids and other N-containing metabolites, and membrane lipids) and phytohormones (brassinosteroids, cytokinins and methylsalicylate) showed the most pronounced modulation. Overall, our results suggest a better performance of A. brasilense in alleviating high salinity than the vegetal-derived protein hydrolysates herein evaluated.

Growth-promoting bacteria and arbuscular mycorrhizal fungi differentially benefit tomato and corn depending upon the supplied form of phosphorus.

The ability of plants to take up phosphorus (P) from soil depends on root morphology and root exudates release and can be modulated by beneficial soil microbes. These microbes can solubilize P, affect root elongation and branching, and lead to a higher uptake of P and other nutrients. However, coordination of these mechanisms is unclear, especially the mechanism for changing the available form of P. We aimed to dissect the effects of two different beneficial microbial taxa (plant growth-promoting bacteria (PGPB) and arbuscular mycorrhizal fungi (AMF)) on root morphological traits, plant nutrient content, and growth in tomato and corn fertilized with either Gafsa rock phosphate (RP) or triple superphosphate (TSP), which have contrasting solubility levels. Tomato and corn were grown in pots and inoculated with one of three PGPB species or a mix of two AMF species or were not inoculated. Root traits, botanical fractions, and the contents of various mineral nutrients were measured. TSP stimulated tomato biomass accumulation compared to RP but did not stimulate corn biomass accumulation. PGPB improved the growth of both plant species under RP, with limited differences among the strains, whereas AMF only improved tomato growth under TSP. These differences between microbial systems were explained by a bacterial effect on the total root length but not on the mean root diameter and by the ability of AMF to improve the mineral nutrient content. The effects of PGPB were less dependent on the plant species and on P form than the effects of AMF.These results have implications for the improvement of the early plant growth through the management of beneficial microbes.

Metabolic Insights into the Anion-Anion Antagonism in Sweet Basil: Effects of Different Nitrate/Chloride Ratios in the Nutrient Solution.

Sweet basil (Ocimum basilicum L.) is a highly versatile and globally popular culinary herb, and a rich source of aromatic and bioactive compounds. Particularly for leafy vegetables, nutrient management allows a more efficient and sustainable improvement of crop yield and quality. In this work, we investigated the effects of balanced modulation of the concentration of two antagonist anions (nitrate and chlorine) in basil. Specifically, we evaluated the changes in yield and leaf metabolic profiles in response to four different NO3-:Cl- ratios in two consecutive harvests, using a full factorial design. Our work indicated that the variation of the nitrate-chloride ratio exerts a large effect on both metabolomic profile and yield in basil, which cannot be fully explained only by an anion-anion antagonist outcome. The metabolomic reprogramming involved different biochemical classes of compounds, with distinctive traits as a function of the different nutrient ratios. Such changes involved not only a response to nutrients availability, but also to redox imbalance and oxidative stress. A network of signaling compounds, including NO and phytohormones, underlined the modeling of metabolomic signatures. Our work highlighted the potential and the magnitude of the effect of nutrient solution management in basil and provided an advancement towards understanding the metabolic response to anion antagonism in plants.

Phytochemical Profile, Mineral Content, and Bioactive Compounds in Leaves of Seed-Propagated Artichoke Hybrid Cultivars.

The globe artichoke (Cynara cardunculus L. subsp. Scolymus (L.) Hegi) is a multi-year species rich in various classes of phytochemicals with known nutritional and pharmacological properties, such as polyphenols, sesquiterpene lactones, and terpenoids. Over the last decade, hybrids cultivars are transforming the artichoke market for their higher uniformity and stability over the traditional landraces, further increasing the potential of the artichoke as a source of commercial extracts and bioactive molecules. Our aim was to investigate the mineral and phytochemical profiles of leaves from seven seed-propagated hybrids by using an untargeted metabolomic approach based on ultra-high-pressure liquid chromatography coupled with quadrupole-time-of-flight mass spectrometry. Metabolomics identified several compounds in the tested varieties, namely 98 polyphenols, 123 sesquiterpene lactones, and 221 other metabolites. The phenolic content ranged from 3.01 mg Eq./g fw (for 'Opera') to 4.71 mg Eq./g fw (for 'Opal'). Sesquiterpene lactones were, on average, 2.11 mg Eq./g fw. Multivariate statistics (HCA, PCA and OPLS-DA) highlighted the main metabolomics differences among cultivars, which weakly correlated with their agronomic classification. The seven cultivars showed distinctive metabolomics profiles, with 'Opal' and 'Istar' being the most valuable hybrids. The 3-hydroxyphenyl-valeric acid (a medium-chain fatty acid) and the 6-Gingesulfonic acid (a methoxyphenol) were the most discriminant markers. Our findings illustrated the quantitative and qualitative variation of several classes of phytochemicals in seed-propagated artichoke cultivars and allowed identifying distinctive metabolic signatures for both phenolic compounds and sesquiterpene lactones. This work supports the exploitation of the artichoke leaves from hybrid cultivars as a rich source of bioactive phytochemicals.

Co-inoculation of Glomus intraradices and Trichoderma atroviride acts as a biostimulant to promote growth, yield and nutrient uptake of vegetable crops.

BACKGROUND: The application of beneficial microorganisms at transplanting can promote rapid transplant establishment (starter effect) for achieving early and high yields. The aim of this study was to evaluate the biostimulant effects of Glomus intraradices BEG72 (G) and Trichoderma atroviride MUCL 45632 (T) alone or in combination on plant growth parameters, yield, chlorophyll index (SPAD), chlorophyll fluorescence and mineral composition of several vegetable crops. RESULTS: The T. atroviride strain was capable of producing siderophores and auxin-like compounds under a wide range of substrate pH conditions (5.5-8.0). The highest shoot, root dry weight, SPAD and chlorophyll fluorescence in lettuce, tomato and zucchini was observed in the G + T combination, followed by a single inoculation of G or T, whereas the lowest values were recorded in the uninoculated plants. Under greenhouse conditions, the shoot dry weight was significantly increased by 167%, 56%, 115%, 68% and 58% in lettuce, melon, pepper, tomato and zucchini, respectively, when supplied with both beneficial microorganisms in comparison with the control. This increase in root and shoot weight was associated with an increased level of nutrient uptake (e.g. P, Mg, Fe, Zn and B). Under open field conditions, the lettuce shoot and root dry weight increased by 61% and 57%, respectively, with biostimulant microorganism application in field conditions. For zucchini, early and total yields were significantly increased by 59% and 15%, respectively, when plants were inoculated with both microorganisms. CONCLUSION: The application of the biostimulant tablet containing both G and T can promote transplant establishment and vegetable crop productivity in a sustainable way.

Salinity source-induced changes in yield, mineral composition, phenolic acids and flavonoids in leaves of artichoke and cardoon grown in floating system.

BACKGROUND: Leaves of artichoke (Cynara cardunculus L. subsp. scolymus (L.) Hegi) and cardoon (Cynara cardunculus L. var. altilis DC) are traditionally used as herbal medicine. Moderate salt stress could enhance antioxidant activity and phytochemicals in leaves. The aim of this study was to evaluate the effect of chloride salts (NaCl, KCl and CaCl2) on biomass production, mineral composition, phenolic and flavonoid contents and antioxidant activity in leaves of artichoke and cardoon grown in a floating system. RESULTS: In both crops, NaCl and KCl treatments reduced biomass production, while similar values were recorded in CaCl2 and control treatments. In both crops, KCl treatment enhanced total phenolic and flavonoid contents, antioxidant activity and target polyphenols in leaves harvested at 48, 82 and 105 days after sowing (DAS), while leaf quality was improved by NaCl and CaCl2 treatments only at 82 and 105 DAS. Irrespective of salinity, leaves of cardoon had higher total phenolic and flavonoid contents, antioxidant activity and target polyphenols than those of artichoke. CONCLUSION: The results showed that application of KCl can be considered an effective way to produce high-quality leaves of artichoke and cardoon during the whole cropping cycle, although resulting in a 30% reduction in plant biomass.

An Appraisal of Nonmicrobial Biostimulants' Impact on the Productivity and Mineral Content of Wild Rocket (Diplotaxis tenuifolia (L.) DC.) Cultivated under Organic Conditions.

Modern agriculture urgently requires viable alternatives to synthetic chemical substances, such as pesticides and fertilizers, to comply with new and stringent international regulations and meet the growing demands of consumers who prefer chemical-free food. Consequently, organic agriculture has garnered increasing interest over time. To compensate for yield reduction resulting from opting out of the use mineral fertilizers, research has focused on the use of biostimulants to sustain the productivity of horticultural crops. To this end, a greenhouse experiment was conducted to assess the effects of three nonmicrobial biostimulants (a plant extract, vegetable protein hydrolysate, and a seaweed extract) and an untreated control on the production and mineral content of wild rocket (Diplotaxis tenuifolia (L.) DC.) cultivated under organic conditions and harvested three times during the growth cycle. In general, the nitrate content, which defines the commercial quality of wild rocket, was not influenced by the application of biostimulants. At each harvest, the application of biostimulants resulted in improved production performance, although this was not always accompanied by an increase in mineral content. Specifically, the best results were obtained with the use of plant-derived protein hydrolysate and plant extract, which led to an improvement in total yield of 32.1% and 27.2%, respectively compared to that of control plants. These results reconfirm that biostimulants represent a valid and indispensable tool for organic growers.

Protein hydrolysates enhance recovery from drought stress in tomato plants: phenomic and metabolomic insights.

Introduction: High-throughput phenotyping technologies together with metabolomics analysis can speed up the development of highly efficient and effective biostimulants for enhancing crop tolerance to drought stress. The aim of this study was to examine the morphophysiological and metabolic changes in tomato plants foliarly treated with two protein hydrolysates obtained by enzymatic hydrolysis of vegetal proteins from Malvaceae (PH1) or Fabaceae (PH2) in comparison with a control treatment, as well as to investigate the mechanisms involved in the enhancement of plant resistance to repeated drought stress cycles. Methods: A phenotyping device was used for daily monitoring morphophysiological traits while untargeted metabolomics analysis was carried out in leaves of the best performing treatment based on phenotypic results.Results: PH1 treatment was the most effective in enhancing plant resistance to water stress due to the better recovery of digital biomass and 3D leaf area after each water stress event while PH2 was effective in mitigating water stress only during the recovery period after the first drought stress event. Metabolomics data indicated that PH1 modified primary metabolism by increasing the concentration of dipeptides and fatty acids in comparison with untreated control, as well as secondary metabolism by regulating several compounds like phenols. In contrast, hormones and compounds involved in detoxification or signal molecules against reactive oxygen species were downregulated in comparison with untreated control. Conclusion: The above findings demonstrated the advantages of a combined phenomics-metabolomics approach for elucidating the relationship between metabolic and morphophysiological changes associated with a biostimulant-mediated increase of crop resistance to repeated water stress events.

Enriching NPK Mineral Fertilizer with Plant-Stimulating Peptides Increases Soilless Tomato Production, Grower Profit, and Environmental Sustainability.

The need to increase agricultural production to feed a steadily growing population may clash with the more environmentally friendly but less efficient production methods required. Therefore, it is important to try to reduce the use of chemical inputs without compromising production. In this scenario, natural biostimulants have become one of the most sought-after and researched technologies. In the present study, the results of a greenhouse experiment on hydroponic tomatoes (Solanum lycopersicum L.) are presented, which involved comparing the use of ordinary NPK fertilizer (Cerbero®) with the use of NPK fertilizers enriched with 0.5% protein hydrolysate of plant origin (Cerbero Green®) at both standard (100%) and reduced (70%) fertilization rates. The results highlight how the use of Cerbero Green® fertilizers improves the production performance of tomatoes. More specifically, they show that the use of Cerbero Green® leads to higher marketable yields, especially under reducing fertilizer use, ensuring a positive net change in profit for the grower. In addition, carbon footprint analysis has revealed that the use of Cerbero Green® reduces the environmental impact of hydroponic tomato growing practices by up to 8%. The observed higher yield of hydroponically grown tomatoes even with reduced fertilization rates underlines once again the key role of natural biostimulants in increasing both the economic and environmental sustainability of horticultural production.

Integrated multi-omic approach reveals the effect of a Graminaceae-derived biostimulant and its lighter fraction on salt-stressed lettuce plants.

Plant biostimulants are widely applied in agriculture for their ability to improve plant fitness. In the present work, the impact of Graminaceae-derived protein hydrolysate (P) and its lighter molecular fraction F3 (< 1 kDa) on lettuce plants, subjected to either no salt or high salt conditions, was investigated through the combination of metabolomics and transcriptomics. The results showed that both treatments significantly modulated the transcriptome and metabolome of plants under salinity stress, highlighting an induction of the hormonal response. Nevertheless, P and F3 also displayed several peculiarities. F3 specifically modulated the response to ethylene and MAPK signaling pathway, whereas P treatment induced a down-accumulation of secondary metabolites, albeit genes controlling the biosynthesis of osmoprotectants and antioxidants were up-regulated. Moreover, according with the auxin response modulation, P promoted cell wall biogenesis and plasticity in salt-stressed plants. Notably, our data also outlined an epigenetic control of gene expression induced by P treatment. Contrarily, experimental data are just partially in agreement when not stressed plants, treated with P or F3, were considered. Indeed, the reduced accumulation of secondary metabolites and the analyses of hormone pathways modulation would suggest a preferential allocation of resources towards growth, that is not coherent with the down-regulation of the photosynthetic machinery, the CO2 assimilation rate and leaves biomass. In conclusion, our data demonstrate that, although they might activate different mechanisms, both the P and F3 can result in similar benefits, as far as the accumulation of protective osmolytes and the enhanced tolerance to oxidative stress are concerned. Notably, the F3 fraction exhibits slightly greater growth promotion effects under high salt conditions. Most importantly, this research further corroborates that biostimulants' mode of action is dependent on plants' physiological status and their composition, underscoring the importance of investigating the bioactivity of the different molecular components to design tailored applications for the agricultural practice.

Effects of saline stress on mineral composition, phenolic acids and flavonoids in leaves of artichoke and cardoon genotypes grown in floating system.

BACKGROUND: Cynara cardunculus is a species native to the Mediterranean basin. It includes globe artichoke and cultivated cardoon as well as their progenitor wild cardoon. The species is a source of biophenols, and its leaf extracts have been widely used in herbal medicine as hepatoprotectors and choleretics since ancient times. The aim of this study was to determine the effect of increasing the level of salinity in the nutrient solution (1 or 30 mmol L⁻¹ NaCl) on biomass production, mineral composition, radical-scavenging activity, caffeoylquinic acids and flavonoids in three artichoke ('Romolo', 'Violetto di Provenza' and 'Violetto di Romagna') and three cultivated cardoon ('Bianco Avorio', 'Bianco Gigante Inerme' and 'Gigante di Romagna') cultivars grown in a floating system. RESULTS: Increased salinity in the nutrient solution decreased the leaf dry biomass and leaf number of artichoke and cultivated cardoon cultivars. Salinity reduced macro- and microelement accumulation in leaves (e.g. N, K, Ca, Mg, Fe, Mn and B) but improved their antioxidant activity, total polyphenols, chlorogenic acid, cynarin and luteolin. The cultivated cardoons, especially 'Bianco Avorio' and 'Gigante di Romagna', showed higher biomass and leaf number than those observed in artichoke genotypes. 'Violetto di Provenza' exhibited the highest content of chlorogenic acid, closely followed by 'Violetto di Romagna', whereas for cynarin content the highest values were recorded in 'Violetto di Provenza', 'Bianco Avorio' and 'Gigante di Romagna'. The highest content of luteolin was recorded in 'Gigante di Romagna' and 'Bianco Avorio', while the highest content of apigenin was observed in 'Gigante di Romagna'. CONCLUSION: The results showed that the floating system could be considered an effective tool to improve quality aspects through proper management of the salt concentration in the nutrient solution. They also suggest that specific cultivars should be selected to obtain the desired profile of bioactive compounds.

Different vegetal protein hydrolysates distinctively alleviate salinity stress in vegetable crops: A case study on tomato and lettuce.

Plants have evolved diverse plant-species specific tolerance mechanisms to cope with salt stress. However, these adaptive strategies often inefficiently mitigate the stress related to increasing salinity. In this respect, plant-based biostimulants have gained increasing popularity since they can alleviate deleterious effects of salinity. Hence, this study aimed to evaluate the sensitivity of tomato and lettuce plants grown under high salinity and the possible protective effects of four biostimulants based on vegetal protein hydrolysates. Plants were set in a 2 × 5 factorial experimental design completely randomized with two salt conditions, no salt (0 mM) and high salt (120 mM for tomato or 80 mM for lettuce), and five biostimulant treatments (C: Malvaceae-derived, P: Poaceae-derived, D: Legume-derived commercial 'Trainer®', H: Legume-derived commercial 'Vegamin®', and Control: distilled water). Our results showed that both salinity and biostimulant treatments affected the biomass accumulation in the two plant species, albeit to different extents. The salinity stress induced a higher activity of antioxidant enzymes (e.g., catalase, ascorbate peroxidase, guaiacol peroxidase and superoxide dismutase) and the overaccumulation of osmolyte proline in both lettuce and tomato plants. Interestingly, salt-stressed lettuce plants showed a higher accumulation of proline as compared to tomato plants. On the other hand, the treatment with biostimulants in salt-stressed plants caused a differential induction of enzymatic activity depending on the plant and the biostimulant considered. Overall, our results suggest that tomato plants were constitutively more tolerant to salinity than lettuce plants. As a consequence, the effectiveness of biostimulants in alleviating high salt concentrations was more evident in lettuce. Among the four biostimulants tested, P and D showed to be the most promising for the amelioration of salt stress in both the plant species, thereby suggesting their possible application in the agricultural practice.

Modulation of Morpho-Physiological and Metabolic Profiles of Lettuce Subjected to Salt Stress and Treated with Two Vegetal-Derived Biostimulants.

Salinity in water and soil is a critical issue for food production. Using biostimulants provides an effective strategy to protect crops from salinity-derived yield losses. The research supports the effectiveness of protein hydrolysate (PH) biostimulants based on their source material. A greenhouse experiment was performed on lettuce plants under control (0 mM NaCl) and high salinity conditions (30 mM NaCl) using the Trainer (T) and Vegamin (V) PH biostimulants. The recorded data included yield parameters, mineral contents, auxiliary pigments, and polyphenolics. The plant sample material was further analyzed to uncover the unique metabolomic trace of the two biostimulants. The results showed an increased yield (8.9/4.6%, T/V) and higher photosynthetic performance (14%) compared to control and salinity treatments. Increased yield in salinity condition by T compared to V was deemed significant due to the positive modulation in stress-protecting molecules having an oxidative stress relief effect such as lutein (39.9% 0 × T vs. 30 × V), ß-carotene (23.4% vs. V overall), and flavonoids (27.7% vs. V). The effects of PH biostimulants on the physio-chemical and metabolic performance of lettuce plants are formulation dependent. However, they increased plant growth under stress conditions, which can prove profitable.

Copper boosts the biostimulant activity of a vegetal-derived protein hydrolysate in basil: morpho-physiological and metabolomics insights.

In addition to be used as a plant protection agent, copper (Cu) is also an essential micronutrient for plant growth and development. The bioavailability of Cu in agricultural systems can be limited due to its specific physical-chemical characteristics, leading to imbalances in plant production. To address this issue, an experimental trial was conducted on Genovese basil (Ocimum basilicum L.) in protected conditions to comparatively evaluate the effects of a vegetable protein hydrolysate (VPH), free Cu and Cu complexed with peptides and amino acids of vegetal origin (Cu and Cu-VPH, respectively), and a combination of VPH and Cu-VPH (VPH+Cu-VPH). The study showed that the combined application of VPH+Cu-VPH led to a significant average increase of 16.3% in fresh yield compared to the untreated Control and Cu treatment. This finding was supported by an improved photosynthetic performance in ACO2 (+29%) and Fv/Fm (+7%). Furthermore, mineral analysis using ICP OES demonstrated that Cu and Cu-VPH treatments determined, on average, a 15.1-, 16.9-, and 1.9-fold increase in Cu in plant tissues compared to control, VPH, and VPH+Cu-VPH treatments, respectively. However, the VPH+Cu-VPH treatment induced the highest contents of the other analyzed ions, except for P. In particular, Mg, Mn, Ca, and Fe, which take part in the constitution of chlorophylls, water splitting system, and photosynthetic electron transport chain, increased by 23%, 21%, 25%, and 32% compared to respective controls. Indeed, this improved the photosynthetic efficiency and the carboxylation capacity of the plants, and consequently, the physiological and productive performance of Genovese basil, compared to all other treatments and control. Consistently, the untargeted metabolomics also pointed out a distinctive modulation of phytochemical signatures as a function of the treatment. An accumulation of alkaloids, terpenoids, and phenylpropanoids was observed following Cu treatment, suggesting an oxidative imbalance upon metal exposure. In contrast, a mitigation of oxidative stress was highlighted in Cu-VPH and VPH+Cu-VPH, where the treatments reduced stress-related metabolites. Overall, these results highlight an interaction between Cu and VPH, hence paving the way towards the combined use of Cu and biostimulants to optimize agronomic interventions.

Plant salinity stress, sensing, and its mitigation through WRKY.

Salinity or salt stress has deleterious effects on plant growth and development. It imposes osmotic, ionic, and secondary stresses, including oxidative stress on the plants and is responsible for the reduction of overall crop productivity and therefore challenges global food security. Plants respond to salinity, by triggering homoeostatic mechanisms that counter salt-triggered disturbances in the physiology and biochemistry of plants. This involves the activation of many signaling components such as SOS pathway, ABA pathway, and ROS and osmotic stress signaling. These biochemical responses are accompanied by transcriptional modulation of stress-responsive genes, which is mostly mediated by salt-induced transcription factor (TF) activity. Among the TFs, the multifaceted significance of WRKY proteins has been realized in many diverse avenues of plants' life including regulation of plant stress response. Therefore, in this review, we aimed to highlight the significance of salinity in a global perspective, the mechanism of salt sensing in plants, and the contribution of WRKYs in the modulation of plants' response to salinity stress. This review will be a substantial tool to investigate this problem in different perspectives, targeting WRKY and offering directions to better manage salinity stress in the field to ensure food security.

Plant biostimulants as natural alternatives to synthetic auxins in strawberry production: physiological and metabolic insights.

The demand for high-quality strawberries continues to grow, emphasizing the need for innovative agricultural practices to enhance both yield and fruit quality. In this context, the utilization of natural products, such as biostimulants, has emerged as a promising avenue for improving strawberry production while aligning with sustainable and eco-friendly agricultural approaches. This study explores the influence of a bacterial filtrate (BF), a vegetal-derived protein hydrolysate (PH), and a standard synthetic auxin (SA) on strawberry, investigating their effects on yield, fruit quality, mineral composition and metabolomics of leaves and fruits. Agronomic trial revealed that SA and BF significantly enhanced early fruit yield due to their positive influence on flowering and fruit set, while PH treatment favored a gradual and prolonged fruit set, associated with an increased shoot biomass and sustained production. Fruit quality analysis showed that PH-treated fruits exhibited an increase of firmness and soluble solids content, whereas SA-treated fruits displayed lower firmness and soluble solids content. The ionomic analysis of leaves and fruits indicated that all treatments provided sufficient nutrients, with heavy metals within regulatory limits. Metabolomics indicated that PH stimulated primary metabolites, while SA and BF directly affected flavonoid and anthocyanin biosynthesis, and PH increased fruit quality through enhanced production of beneficial metabolites. This research offers valuable insights for optimizing strawberry production and fruit quality by harnessing the potential of natural biostimulants as viable alternative to synthetic compounds.