Higher Plant-Derived Biostimulants: Mechanisms of Action and Their Role in Mitigating Plant Abiotic Stress

Abstract

Modern agriculture is being challenged by deteriorating edaphoclimatic conditions and increasing anthropogenic pressure. This necessitates the development of innovative crop production systems that can sustainably meet the demands of a growing world population while minimizing the environmental impact. The use of plant biostimulants is gaining ground as a safe and ecologically sound approach to improving crop yields. In this review, biostimulants obtained from different higher plant sources are presented under the term higher plant-derived biostimulants (hPDBs). Their mechanisms of action regulate physiological processes in plants from germination to fructification, conditioned by responses induced in plant mineral nutrition and primary metabolism, specialized metabolism, photosynthetic processes, oxidative metabolism, and signaling-related processes. The aim of this review is to collect and unify the abundant information dispersed in the literature on the effects of these biostimulants, focusing on crops subjected to abiotic stress conditions and the underlying mechanisms of action.

Assessing the Effect of Plant Biostimulants and Nutrient-Rich Foliar Sprays on Walnut Nucleolar Activity and Protein Content (Juglans regia L.)

“…The growing world population and climate change are causing the demand for higher crop productivity and food security to increase [6]. However, such pressure imposes challenges to agriculture in terms of reliability, sustainability, and maximisation of productivity Horticulturae 2024, 10, 314 2 of 13 while reducing negative impacts on human health and the environment [7][8][9].…”

“…However, such pressure imposes challenges to agriculture in terms of reliability, sustainability, and maximisation of productivity Horticulturae 2024, 10, 314 2 of 13 while reducing negative impacts on human health and the environment [7][8][9]. An innovative technology to tackle these issues is the foliar application of plant biostimulants (PBs), which, in general, can enhance or modify physiological processes to optimise plant growth, productivity and abiotic stress tolerance [6][7][8][9][10][11][12][13]. Despite producers' and enterprises' wide use of PBs, further knowledge about their effects on the plant and environment should be gathered to contribute to treatment efficacy and food security.…”

“…PBs are complex mixtures of raw substances with synergistic/antagonistic effects whose effectiveness depends on various factors, such as the plant genetic variability, environmental conditions, and mode of action, limiting the categorisation and commercialisation of new formulations [6,12,[14][15][16]. There are few PBs for which a specific biochemical or molecular target and mode of action have been identified [12].…”

“…However, for a small subset of PB, their impacts on general biochemical and molecular pathways and physiological processes were designated as "mechanisms of action" by [12]. As PBs have not been characterised enough at specific levels to establish their modes of action, transcriptomics, proteomics, metabolomics, and high-throughput phenotyping have been contributing to unravelling their mechanisms of action [6]. These authors reviewed the mechanisms of action of PBs at the molecular and cellular levels (e.g., plant mineral nutrition, primary and specialised metabolism, photosynthetic processes, oxidative metabolism, signallingrelated processes) and at the whole-plant level (germination, root and shoot growth and morphology, flowering, fructification, and fruit quality) [6].…”

Plant Biostimulants Enhance Tomato Resilience to Salinity Stress: Insights from Two Greek Landraces

“…A novel approach for stress mitigation relies on the application of plant biostimulants (PBs) [20][21][22][23][24][25]. PBs are increasingly being incorporated into agricultural systems to adjust physiological functions of plants, thereby enhancing productivity [26][27][28].…”