Root ABA and H⁺‐ATPase are key players in the root and shoot growth‐promoting action of humic acids

Abstract

Although the ability of humic (HA) and fulvic acids (FA) to improve plant growth has been demonstrated, knowledge about the mechanisms responsible for the direct effects of HA and FA on the promotion of plant growth is scarce and fragmentary. Our study investigated the causal role of both root PM H+‐ATPase activity and ABA in the SHA‐promoting action on both root and shoot growth. The involvement of these processes in the regulation of shoot cytokinin concentration and activity was also studied. Our aim was to integrate such plant responses for providing new insights to the current model on the mode of action of HA for promoting root and shoot growth. Experiments employing specific inhibitors and using Cucumis sativus L. plants show that both the root PM H+‐ATPase activity and root ABA play a crucial role in the root growth‐promoting action of SHA. With regard to the HA‐promoting effects on shoot growth, two pathways of events triggered by the interaction of SHA with plant roots are essential for the increase in root PM H+‐ATPase activity—which also mediates an increase in cytokinin concentration and action in the shoot—and the ABA‐mediated increase in hydraulic conductivity (Lpr).

Enhanced Agronomic Efficiency Using a New Controlled-Released, Polymeric-Coated Nitrogen Fertilizer in Rice

“…Using biostimulants as amino acids, humic and/or fulvic acids or extracts of algae can increase the resistance of cultures against abiotic stress and may also influence the hormonal balance of plants [ 51 , 52 , 53 ]. More specifically, and in agreement with the results of the present work, a recent study demonstrated that humic acids increase the root plasma membrane H + -ATPase activity, which in turn, among other effects, mediates an increase in cytokinin concentration in the shoots [ 54 ].…”

Discriminating the Short-Term Action of Root and Foliar Application of Humic Acids on Plant Growth: Emerging Role of Jasmonic Acid

“…In agreement with previous results on the application of HS to plant leaves (Rose et al, 2014;Canellas et al, 2015), foliarapplied SHA was found to promote significant increases in both shoot and root dry matter at the concentration of 40 mg C L −1 (SHA.F40) (Figure 1). These results are in line with the results obtained with root-applied SHA in cucumber plants cultivated in hydroponics under the same environmental and nutritional conditions as that used in the present study (Aguirre et al, 2009;Mora et al, 2010Mora et al, , 2012Mora et al, , 2014Olaetxea et al, 2015Olaetxea et al, , 2019. In principle, these results indicate that SHA is able to promote plant growth regardless the mode of application.…”

“…Hence, the aim of this study is to evaluate some of the mechanisms triggered after foliar application of a wellcharacterized sedimentary humic acid (SHA) previously found to improve plant growth when applied to roots (Aguirre et al, 2009;Mora et al, 2010Mora et al, , 2012Mora et al, , 2014Olaetxea et al, 2015Olaetxea et al, , 2019. Our hypothesis is that the interaction of HS with plant leaves might induce some kind of mild stress signals that may activate hormonal and molecular pathways involved in the regulation of plant stress responses.…”

Interaction between Humic Substances and Plant Hormones for Phosphorous Acquisition

“…Underlying mechanisms include the multiple functions of HS as: (1) a chelator, making P more available in soil solution [27,84,85], and (2) a stimulator of root PM-ATPase (referred to as an "auxin-like effect"), which alters root growth and architecture [33,80]. In the latter mechanism, other hormones, ET [44], nitric oxide (NO) [45,86] and ABA [39,87] are mediated by HA. Shah and colleagues [88] describe three growth-triggering pathways which involve the link between HS treatment, gene expression of the aforementioned hormones, and NO modulation.…”

“…In addition to CK as a regulator of root-shoot nutrient distribution, ABA also regulates shoot growth by altering root hydraulic conductivity. Several studies by Olaetxea et al [39,66,87,89] revealed that high shoot growth resulted from increased ABA concentration in root following HA treatment, consequently enhancing root hydraulic conductivity.…”