Chemical Structure and Biological Activity of Humic Substances Define Their Role as Plant Growth Promoters

Humic substances (HS) are dominant components of soil organic matter and are recognized as natural, effective growth promoters to be used in sustainable agriculture. In recent years, many efforts have been made to get insights on the relationship between HS chemical structure and their biological activity in plants using combinatory approaches. Relevant results highlight the existence of key functional groups in HS that might trigger positive local and systemic physiological responses via a complex network of hormone-like signaling pathways. The biological activity of HS finely relies on their dosage, origin, molecular size, degree of hydrophobicity and aromaticity, and spatial distribution of hydrophilic and hydrophobic domains. The molecular size of HS also impacts their mode of action in plants, as low molecular size HS can enter the root cells and directly elicit intracellular signals, while high molecular size HS bind to external cell receptors to induce molecular responses. Main targets of HS in plants are nutrient transporters, plasma membrane H⁺-ATPases, hormone routes, genes/enzymes involved in nitrogen assimilation, cell division, and development. This review aims to give a detailed survey of the mechanisms associated to the growth regulatory functions of HS in view of their use in sustainable technologies.     

Insights on Molecular Characteristics of Hydrochars by 13C-NMR and Off-Line TMAH-GC/MS and Assessment of Their Potential Use as Plant Growth Promoters

Hydrochar is a carbon-based material that can be used as soil amendment. Since the physical-chemical properties of hydrochar are mainly assigned to process parameters, we aimed at evaluating the organic fraction of different hydrochars through ¹³C-NMR and off-line TMAH-GC/MS. Four hydrochars produced with sugarcane bagasse, vinasse and sulfuric or phosphoric acids were analyzed to elucidate the main molecular features. Germination and initial growth of maize seedlings were assessed using hydrochar water-soluble fraction to evaluate their potential use as growth promoters. The hydrochars prepared with phosphoric acid showed larger amounts of bioavailable lignin-derived structures. Although no differences were shown about the percentage of maize seeds germination, the hydrochar produced with phosphoric acid promoted a better seedling growth. For this sample, the greatest relative percentage of benzene derivatives and phenolic compounds were associated to hormone-like effects, responsible for stimulating shoot and root elongation. The reactions parameters proved to be determinant for the organic composition of hydrochar, exerting a strict influence on molecular features and plant growth response.     

芴三偶氮基水杨醛缩氨基芳基硫脲合成及其植物生长调节作用

以芴、水杨醛和氨基芳基硫脲为原料合成了一系列新型芴三偶氮基水杨醛缩氨基芳基硫脲衍生物,其结构经IR、1H NMR、MS和元素分析测试技术确证。经平皿油菜生根实验表明,该类化合物在低浓度下对油菜生根显示促进作用,高浓度下促进作用小或显示抑制作用,对油菜生根的调节作用与硫脲的苯取代基上的取代基性质有关。     

Integrated Metabolome and Lipidome Strategy to Reveal the Action Pattern of Paclobutrazol,a Plant Growth Retardant,in Varying the Chemical Constituents of Platycodon Root

Platycodon root, a medicinal food homology species which has been used in Asian countries for hundreds of years, is now widely cultivated in China. Treatment with paclobutrazol, a typical plant growth retardant, has raised uncertainties regarding the quality of Platycodon root, which have been rarely investigated. In the present study, metabolomic and lipidomic differences were revealed by ultra-high performance liquid chromatography coupled to ion mobility-quadrupole time of flight mass spectrometry (UPLC-IM-QTOF-MS). A significant decrease of platycodigenin-type saponins was observed in the paclobutrazol-treated sample. Carrying out a comprehensive quantitative analysis, the contents of total saponins and saccharides were determined to illustrate the mode of action of paclobutrazol on Platycodon root. This study demonstrated an exemplary research model in explaining how the exogenous matter influences the chemical properties of medicinal plants, and therefore might provide insights into the reasonable application of plant growth regulators.