Recent Advances in the Molecular Effects of Biostimulants in Plants: An Overview

Abstract

As the world develops and population increases, so too does the demand for higher agricultural output with lower resources. Plant biostimulants appear to be one of the more prominent sustainable solutions, given their natural origin and their potential to substitute conventional methods in agriculture. Classified based on their source rather than constitution, biostimulants such as humic substances (HS), protein hydrolysates (PHs), seaweed extracts (SWE) and microorganisms have a proven potential in improving plant growth, increasing crop production and quality, as well as ameliorating stress effects. However, the multi-molecular nature and varying composition of commercially available biostimulants presents challenges when attempting to elucidate their underlying mechanisms. While most research has focused on the broad effects of biostimulants in crops, recent studies at the molecular level have started to unravel the pathways triggered by certain products at the cellular and gene level. Understanding the molecular influences involved could lead to further refinement of these treatments. This review comprises the most recent findings regarding the use of biostimulants in plants, with particular focus on reports of their molecular influence.

Biostimulants to Improved Tree Physiology and Fruit Quality: A Review with Special Focus on Sweet Cherry

“…Another category of biostimulants is protein-based products, which can be divided into protein hydrolysates (PHs) (a mixture of peptides and amino acids of animal or plant origin) individual amino acids (glutamate, glutamine, proline) and glycine betaine [32,33]. The former is prepared by several approaches, namely enzymatic, chemical, or thermal hydrolysis from animal and plant residues [28,34].…”

“…PHs' application is mainly foliar, although they are also applied to substrate and seeds [36]. PHs have demonstrated, both in open field and in greenhouses, the ability to increase nutrient absorption, density, length, and number of lateral roots [33,37], as well as improved enzymatic activity, increased photosynthetic rate and stomatal conductance, plant growth, and productivity, especially under environmental stress conditions [5,[38][39][40].…”

“…In their composition, both organic and mineral compounds are present, such as unique and complex polysaccharides, only found in seaweeds, plant hormones [42,46,47], namely cytokinins, auxins, abscisic acid, gibberellins, and other classes of hormone-like compounds, such as sterols and polyamines [41,48]. Polysaccharides are major components of brown seaweeds, and two of the most studied brown macroscopic algae are Ascophyllum nodosum and Ecklonia maxima [33]. There are numerous reports of beneficial effects of the application of these seaweed extracts linked to increases in plant growth and yield parameters as well as an increase of protein and nutrient content [49,50].…”

“…In this group, there are beneficial fungi and bacteria. Fungi-and bacteriabased biostimulants are of particular importance, as they positively influence soil biodiversity, playing an important role in mitigating the impacts of agricultural activity on the environment [33,66] and benefiting plants, regarding their nutrition, productivity, and stress resistance, both abiotic and biotic [67].…”

How Does the Addition of Biostimulants Affect the Growth, Yield, and Quality Parameters of the Snap Bean (Phaseolus vulgaris L.)? How Is This Reflected in Its Nutritional Value?

“…Depending on their composition and expected results, biostimulants can be applied to soil or leaves [8]. Natural stimulants are often included under the term biostimulants, including humic acid, microorganisms (i.e., yeast), moringa leaf extract (MLE), or vermicompost tea extract [9][10][11][12][13]. Although primarily associated with the enhancement of root growth [14], humic acid has also been shown to confer other benefits, such as increasing the mobilization of nutrients; improving photosynthetic rates, respiration, and water balance; and increasing the content of photosynthetic pigments [15].…”