The biostimulants (BS) are an emerging trend that can alleviate the negative effects of climate change on crops and help the transition to greener agriculture. Among the different types of BS, the small molecule-based BS (smbBS), including polyamines (PAs), is an exciting option because of its simple formulation. This work aimed to understand the PA mechanism/mode of action using different omics, especially phenomics performed on the Olophen phenotyping platforms. Firstly, the suitability and accuracy of the platforms using different plant species were evaluated. Secondly, this work was focused on characterizing the application of putrescine (Put) and spermidine (Spd) to understand their mechanism/mode of action. Drenching with Put and Spd improved the yield quantity and quality in maize under a water restriction but Put, and Spd showed different mechanisms of action. Moreover, they affected the mineral composition of the kernels, raising an interesting question of using BS for crop biofortification. An additional experiment using in vitro Arabidopsis plants primed with Put, ornithine (Orn) as its precursor, and 1,3- diaminopropane as a compound of PA terminal catabolism was also performed. Almost all improved the growth of Arabidopsis in vitro seedlings under stress. The metabolic analysis revealed the implication of the N- acetylOrn and Orn and PA conjugation as the leading player regulating growth and development under control and stress conditions. To further understand the Orn involvement in regulating plant stress tolerance, and to evaluate the biological translation from Arabidopsis to a crop with economic value, an experiment on barley (Hordeum vulgare L. cv. Wildtype; WT) and a sensitive mutant (AZ34; AZ) was carried out, using Orn as a foliar application. As a preliminary result, we observed that Orn altered the physiology and metabolism of barley plants differently according to the genotype, pointing to this metabolite as an essential regulator of polyamine metabolism and endogenous abscisic acid and, hence, plants' water stress response.The biostimulants (BS) are an emerging trend that can alleviate the negative effects of climate change on crops and help the transition to greener agriculture. Among the different types of BS, the small molecule-based BS (smbBS), including polyamines (PAs), is an exciting option because of its simple formulation. This work aimed to understand the PA mechanism/mode of action using different omics, especially phenomics performed on the Olophen phenotyping platforms. Firstly, the suitability and accuracy of the platforms using different plant species were evaluated. Secondly, this work was focused on characterizing the application of putrescine (Put) and spermidine (Spd) to understand their mechanism/mode of action. Drenching with Put and Spd improved the yield quantity and quality in maize under a water restriction but Put, and Spd showed different mechanisms of action. Moreover, they affected the mineral composition of the kernels, raising an interesting question of using BS for crop biofortification. An additional experiment using in vitro Arabidopsis plants primed with Put, ornithine (Orn) as its precursor, and 1,3- diaminopropane as a compound of PA terminal catabolism was also performed. Almost all improved the growth of Arabidopsis in vitro seedlings under stress. The metabolic analysis revealed the implication of the N- acetylOrn and Orn and PA conjugation as the leading player regulating growth and development under control and stress conditions. To further understand the Orn involvement in regulating plant stress tolerance, and to evaluate the biological translation from Arabidopsis to a crop with economic value, an experiment on barley (Hordeum vulgare L. cv. Wildtype; WT) and a sensitive mutant (AZ34; AZ) was carried out, using Orn as a foliar application. As a preliminary result, we observed that Orn altered the physiology and metabolism of barley plants differently according to the genotype, pointing to this metabolite as an essential regulator of polyamine metabolism and endogenous abscisic acid and, hence, plants' water stress response.