Potentialities of vermicompost humic acids to alleviate water stress in rice plants (Oryza sativa L.)

• The humic acids (HA) have protective effects in rice plants under water stress.
• Applications of HA in plants under water stress decrease H2O2 and lipid peroxidation.
• The mechanisms are mediated by tonoplast aquaporins (OsTIPs).
• Clusters of HA on the roots have different structure in relation to the HA added.

The aim of this study was to assess the effects of applying humic acid (HA) to rice plants under water stress conditions. HA maintained peroxidase activity below the levels found in plants that were under stress without the addition of HA. Lipid peroxidation in the roots and leaves was lower in the treatments with HA compared to the plants that were under stress that were not treated with HA. Plants that were under water stress and treated with HA maintained abscisic acid levels similar to those of the control plants. HA exerted differential effects on the expression of aquaporin in both root and leaf tissues. Alkyl, carboxylic and carbonyl structures predominated in the agglomerated HA at the roots. These results demonstrate that HA exerted a protective effect possibly through signaling mechanism independent of ABA, regulation of OsTIPs genes and potentially initiated by chemical and physical interactions between HA and the plant root system.