Biostimulants and plant response under adverse environmental conditions: a functional interplay

The innovative agricultural practices are developing towards low-cost and environmentally friendly methods that guarantee yield and high quality of crops. To this aim, biostimulant products have been proposed to improve crop development and productivity and, at the same time, to reduce the use of agrochemicals. Biostimulants, in combination with correct agronomic practices, have beneficial effects on plant metabolism due to the hormonal activity that causes the stimulation of different metabolic pahtways, such as nitrogen and carbon assimilation, as well as the secondary metabolites biosynthesis. Biostimulants include a wide range of products such as seaweed extracts, protein-hydrolyzates, plant extracts, microgranisms, inorganic ions, etc. Protein-hydrolyzates, based biostimulants are mainly produced by enzymatic and/or chemical hydrolysis of proteins from raw materials of animal or plant origin. These products have interested scientists and industries, thanks to the ability to help plants overcoming abiotic stress conditions, as demonstrated by several researches whom highlited the role of bioactive molecules in mediating biochemical responses against stressors and in regulating many other cellular events in plants. These effects have been attributed to the osmolyte and chemical chaperone roles of proline and proline-precursors compounds (glutamate and ornithine) in hydrolysates, under stress conditions. Biostimulants correctly applied can stimulate crop development, increase tolerance against abiotic stresses, improve nutrient and water use efficiency.