{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,6,27]],"date-time":"2026-06-27T06:39:38Z","timestamp":1782542378325,"version":"3.54.5"},"reference-count":120,"publisher":"MDPI AG","issue":"8","license":[{"start":{"date-parts":[[2021,4,13]],"date-time":"2021-04-13T00:00:00Z","timestamp":1618272000000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/licenses\/by\/4.0\/"}],"funder":[{"DOI":"10.13039\/501100003500","name":"Universit\u00e0 degli Studi di Padova","doi-asserted-by":"publisher","award":["DOR2082752\/20"],"award-info":[{"award-number":["DOR2082752\/20"]}],"id":[{"id":"10.13039\/501100003500","id-type":"DOI","asserted-by":"publisher"}]}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["Molecules"],"abstract":"<jats:p>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.<\/jats:p>","DOI":"10.3390\/molecules26082256","type":"journal-article","created":{"date-parts":[[2021,4,13]],"date-time":"2021-04-13T22:55:09Z","timestamp":1618354509000},"page":"2256","update-policy":"https:\/\/doi.org\/10.3390\/mdpi_crossmark_policy","source":"Crossref","is-referenced-by-count":323,"title":["Chemical Structure and Biological Activity of Humic Substances Define Their Role as Plant Growth Promoters"],"prefix":"10.3390","volume":"26","author":[{"ORCID":"https:\/\/orcid.org\/0000-0002-7851-0065","authenticated-orcid":false,"given":"Serenella","family":"Nardi","sequence":"first","affiliation":[{"name":"Department of Agronomy, Food, Natural Resources, Animals and Environment, Universit\u00e0 degli Studi di Padova, V.le dell\u2019Universit\u00e0 16,  Legnaro, 35020 Padova, Italy"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Michela","family":"Schiavon","sequence":"additional","affiliation":[{"name":"Department of di of Agricultural, Forest and Food Sciences (DISAFA), University of Turin, Largo Paolo Braccini 2 (gi\u00e0 Via Leonardo da Vinci, 44), 10095 Grugliasco, Italy"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0003-0643-7441","authenticated-orcid":false,"given":"Ornella","family":"Francioso","sequence":"additional","affiliation":[{"name":"Department of Agricultural and Food Sciences, University of Bologna, Viale G. Fanin, 40, 40127 Bologna, Italy"}],"role":[{"vocabulary":"crossref","role":"author"}]}],"member":"1968","published-online":{"date-parts":[[2021,4,13]]},"reference":[{"key":"ref_1","doi-asserted-by":"crossref","first-page":"3","DOI":"10.1186\/2196-5641-1-3","article-title":"Physiological responses to humic substances as plant growth promoter","volume":"1","author":"Canellas","year":"2014","journal-title":"Chem. Biol. Technol. Agric."},{"key":"ref_2","doi-asserted-by":"crossref","first-page":"5","DOI":"10.1002\/jpln.201600348","article-title":"Soil\u2013root cross\u2014Talking: The role of humic substances","volume":"180","author":"Nardi","year":"2017","journal-title":"J. Plant Nutr. Soil Sci."},{"key":"ref_3","doi-asserted-by":"crossref","unstructured":"Jung, H., Kwon, S., Kim, J.-H., and Jeon, J.-R. (2021). Which traits of humic substances are investigated to improve their agronomical value?. Molecules, 26.","DOI":"10.3390\/molecules26030760"},{"key":"ref_4","unstructured":"(2019). 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