Seed Priming With Protein Hydrolysates Improves Arabidopsis Growth and Stress Tolerance to Abiotic Stresses

Abstract

The use of plant biostimulants contributes to more sustainable and environmentally friendly farming techniques and offers a sustainable alternative to mitigate the adverse effects of stress. Protein hydrolysate-based biostimulants have been described to promote plant growth and reduce the negative effect of abiotic stresses in different crops. However, limited information is available about their mechanism of action, how plants perceive their application, and which metabolic pathways are activating. Here we used a multi-trait high-throughput screening approach based on simple RGB imaging and combined with untargeted metabolomics to screen and unravel the mode of action/mechanism of protein hydrolysates in Arabidopsis plants grown in optimal and in salt-stress conditions (0, 75, or 150 mM NaCl). Eleven protein hydrolysates from different protein sources were used as priming agents in Arabidopsis seeds in three different concentrations (0.001, 0.01, or 0.1 μl ml–1). Growth and development-related traits as early seedling establishment, growth response under stress and photosynthetic performance of the plants were dynamically scored throughout and at the end of the growth period. To effectively classify the functional properties of the 11 products a Plant Biostimulant Characterization (PBC) index was used, which helped to characterize the activity of a protein hydrolysate based on its ability to promote plant growth and mitigate stress, and to categorize the products as plant growth promoters, growth inhibitors and/or stress alleviator. Out of 11 products, two were identified as highly effective growth regulators and stress alleviators because they showed a PBC index always above 0.51. Using the untargeted metabolomics approach, we showed that plants primed with these best performing biostimulants had reduced contents of stress-related molecules (such as flavonoids and terpenoids, and some degradation/conjugation compounds of phytohormones such as cytokinins, auxins, gibberellins, etc.), which alleviated the salt stress response-related growth inhibition.

Integration of Phenomics and Metabolomics Datasets Reveals Different Mode of Action of Biostimulants Based on Protein Hydrolysates in Lactuca sativa L. and Solanum lycopersicum L. Under Salinity

“…Seven PHs obtained by enzymatic hydrolysis of vegetal-derived proteins were selected from a batch of eleven PHs that were previously screened for their mode of action (Sorrentino et al, 2021) and used for the experiment. They included PHs from different plant sources belonging to the botanical families of Fabaceae (O), Malvaceae (C), Brassicaceae (F), Solanaceae (B), and Graminaceae (P), and two commercial products [Trainer R (D) and Vegamin R (H)], commercialised by Hello Nature Inc. (former Italpollina) (Anderson, IN, United States) and used as positive controls.…”

“…The PH was obtained through enzymatic hydrolysis of the dry biomass and was then analysed for their total nitrogen and carbon content. For a detailed description of the procedure, see Sorrentino et al (2021) and Ceccarelli et al (2021).…”

“…To simplify the results and to identify the specific mode of action of the 7 PHs, we used the Plant Biostimulant Characterisation (PBC) index as described previously (Ugena et al, 2018;Sorrentino et al, 2021). For the calculation of the PBC indexes, we selected the five traits (DB, RGR, Fv /Fm , PSII, and T) that provided the highest discriminative power between the different treatments (Supplementary Tables 1-3).…”

“…To determine the index value, the log2 of the ratio between the biostimulant treated plants and untreated ones was determined for each crop and growth conditions, and then represented in parallel plots (Figure 3). Then, the five obtained values represented in each parallel plot were summed to end with a unique number that represents the PBC index (for further detail see Sorrentino et al, 2021) which was included in Table 1. The calculated PBC index for each compound, growing condition, and phase of the trial could be negative (red) or positive (blue), providing information about the mode of action of that specific combination (Table 1).…”

“…However, the PH application will ameliorate the salt negative effect in both plant species. Besides, a deep data analysis using advanced statistical tools will allow us (i) to understand better the effect of the PHs on two species, lettuce and tomato, selected for their economic importance, their distinct architecture, and purpose, and their different sensitivity to salinity stress, (ii) to evaluate the biological translation from the results obtained in PH-primed Arabidopsis grown under salt stress (Sorrentino et al, 2021) to other crops under similar growing conditions, and (iii) to demonstrate the necessity of the use of statistical approaches to simplify complex omic datasets allowing identification of the traits relevant for the understanding of a biostimulant mechanism of action.…”