Biostimulant effects of different products on the metabolism of agro-food plants
Year: 2018
Type: dissertation
Abstract: Sustainable and environmentally friendly agriculture represents the main strategy to meet rising food needs and to contribute to a stable planet. To achieve these goals, one of the most promising solutions is the adoption of plant biostimulants. Biostimulants are natural compounds which, at low concentrations, are able to enhance plant nutrient uptake, nutrient efficiency, tolerance to abiotic/biotic stresses, and crop yield. Humic substances (HS) fall within the biostimulants definition, as they have positive effects on the uptake of macro and micronutrients that considerably improve the metabolism, the growth and yields of relevant agricultural crops. With this background, the aims of this Ph.D. project were to i) evaluate metabolic and biochemical status of plants treated with HS to elucidate the action mechanisms of plant biostimulants. This might permit the development of a second generation of biostimulants where synergies and complementary mechanism can be functionally designed. ii) investigate potential biostimulant effects of a fungicide compound. In manuscript I Arabidopsis thaliana plants were treated with HS for eight hours. Root proteins were studied by MS spectrometry coupled with iTRAQ (Isobaric Tag for Relative and Absolute Quantification) technique. 902 protein spots were identified for HS treated roots, where 291 proteins were differentially expressed. Bioinformatic tools such as DAVID, KEGG, IIS and Cytoscape were used to interpret the biological function, pathway analysis and visualization of the network amongst the identified proteins. From this analysis, it was possible to evaluate that most of the differentially expressed proteins were functionally classified into response to inorganic substances, redox homeostasis, energy metabolism, protein synthesis, cell trafficking and division. With the present study an overview of the metabolic pathways most modified by HS biological activity is provided. Moreover, from the analysis of interactomes and DAVID clusters it was possible to observe previously undiscovered HS effects, i.e. on the Ubiquitin and RACK1A interactome subnetworks. In manuscript II Arabidopsis thaliana plants, grown in hydroponic conditions, were treated for 8 h with indole-3-acetic acid (IAA), HS from International Humic Substances Society (IHSS) and HS from earthworm faeces (EF), respectively. Humic substances structural characteristics were analysed by 1H NMR an FT-IR spectroscopies. Root and leaf free amino acids, sugar alcohols and carbohydrates contents, and leaf amino acids from protein hydrolysis were identified and quantify by gas chromatography-mass spectrometry (GC/MS), and liquid chromatography-mass spectrometry (LC/MS) techniques. Canonical discriminant analysis (CDA) was used to evaluate the influence of the treatments on the studied parameters. EF treatment had the highest influence on metabolites profiles compared to the control, IAA and IHSS. CDA analysis highlighted a clear distinction between EF and IHSS plant physiological responses, depending on the different chemical and structural properties of the HS. IAA-treated plants resulted not significant different from the control. A better understanding of the specific effects of different HS, also related to their chemical characteristics, might serve as a basis for the identification of marker compounds for HS bioactivity. In manuscript III the biostimulant activity of HS extracted from four leonardites is analysed on maize seedlings. After 48 h of treatment with five concentrations (0, 0.1, 0.5, 1, and 10 mg C L−1) of HS, root growth and morphology, glutamine synthetase (GS) activity, glutamate synthase (GOGAT) activity, total protein content, soluble sugars content, phenylalanine ammonia-lyase (PAL) activity, soluble phenols, and free phenolic acids were analyzed. HS from different leonardites had similar spectroscopic pattern, with small differences. HS_USA best enhanced total root growth, root surface area, and proliferation of secondary roots. Plant nutrient use efficiency was enhanced by HS_4, HS_USA and HS_B, with increment of GS and GOGAT enzymes activity and total protein production. HS stimulated also PAL enzyme activity, followed by a higher production of total soluble phenols. This study found that, although the activity of the HS depended on the origin of the leonardite, these compounds can be attributed to the biostimulant products, eliciting plant growth, nitrogen metabolism, and accumulation of phenolic substances. In the manuscript IV it was investigated the potential biostimulant side-effects of sedaxane. Physiological changes in disease-free maize seedlings at increasing application doses (25, 75 and 150 μg a.i. seed-1) under controlled sterilised conditions were analysed. Sedaxane had significant auxin-like and gibberellin-like effects, with maximum benefits attained at the intermediate dose. Root length (+60% vs. untreated controls), area (+45%) and forks (+51%) were significantly increased. Sedaxane enhanced leaf and root glutamine synthetase (GS) activity resulting in greater protein accumulation. Sedaxane also improved leaf phenylalanine ammonia-lyase (PAL) activity, which may be responsible for the increase in shoot antioxidant activity (phenolic acids). It is concluded that, in addition to its protective effect, sedaxane can facilitate root establishment and intensify nitrogen and phenylpropanoid metabolism in young maize plants, and may be beneficial in overcoming biotic and abiotic stresses in early growth stages. As a general conclusion, even if HS were extracted from different sources were applied on different plant species, they displayed similar biological activities. Proteomics and metabolomics studies confirmed that “–omics” techniques are essential tools to have a ‘panoramic’ view on metabolic changes happening inside an organism after a positive or negative external perturbation.
Author: Giovanni Battista Conselvan
Language: English
Subfield: Plant Science
Domain: Life Sciences
SDG: Zero hunger
Open Access status: green
OpenAlex ID: W2904189126