Humic substances induce lateral root formation and expression of the early auxin-responsiveIAA19gene and DR5 synthetic element inArabidopsis

Abstract

Humic substances (HS) have positive effects on plant physiology, but the molecular mechanisms underlying these events are only partially understood. HS exert auxin-like activity, but data supporting this hypothesis are under debate. To investigate the auxin-like activity of HS, we studied their biological effect on lateral root initiation in Arabidopsis thaliana. To this aim we characterised HS by means of DRIFT and (13)C CP/MAS NMR spectroscopy, and measured their endogenous content of IAA. We then utilised a combination of genetic and molecular approaches to unravel HS auxin activity in the initiation of lateral roots. The data obtained using specific inhibitors of auxin transport or action showed that HS induce lateral root formation mostly through their 'auxin activity'. These findings were further supported by the fact that HS used in this study activated the auxin synthetic reporter DR5::GUS and enhanced transcription of the early auxin responsive gene IAA19.

Physiological responses to humic substances as plant growth promoter

“…DR5 auxin synthetic promoter fused to the β-glucuronidase (GUS) reporter gene (DR5::GUS) has been used as a tool to visualize auxin responses in tissues and mark auxin signalling in lateral root primordia at all developmental stages. The first evidence using DR5::GUS tools that HS caused activation of expression of this gene reporter in lateral roots, in a way comparable to exogenously applied auxins, was provided by Trevisan et al [21]. These results were further corroborated by employing tomato (cv.…”

Humic substances stimulate maize nitrogen assimilation and amino acid metabolism at physiological and molecular level

“…In this case, the choice of a 24-h treatment was aimed at evaluating the earlier molecular effects of humic matter. In fact, Trevisan et al [40] showed that the gene transcription in response to HS is regulated already after a few hours of treatment.…”

“…However, because of the complexity of HS' nature, the relationship between their molecular structure and biological activity is not yet completely clear. In the last decades, several studies correlated biological activity to humic chemical features [31][32][33][34][35][36][37][38][39][40][41]. The positive effects of different HS in relation to their chemical structure were shown by Muscolo et al [35] and Nardi et al [36] on Pinus nigra callus metabolism and Zea mays seedling growth.…”

Influence of humic acid and poultry manure on nutrient content and their uptake by T. aman rice

“…Humic acid improves the physical, chemical and biological properties of the soil and influences plant growth. Humic substances are recognised as a key component of soil fertility properties, since they control chemical and biological properties of the rhizosphere (Rengrudkij and Partida, 2003, Nardi et al, 2005, Trevisan et al, 2009). The effects of humic substances have been directly correlated with enhanced uptake of macronutrients, such as N, P and S, and micronutrients like Fe, Zn, Cu and Mn (Pettit, 2004, Chen et al, 2001.…”