Are endophytic bacteria involvedin increasing plant drought tolerance provided by humic and fulvic acids application ?

Abstract

Positive effects of humic and fulvic acids (HA)-based biostimulants on plant tolerance to drought stress are reported in the literature. Little is known on the mechanisms of action of HA but the regulation of hormonal and redox metabolisms within plants is involved. Based on a plant study model under controlled conditions, the effect of HA in increasing drought stress resistance is assessed and the potential role of bacterial endophytic community in this processis analyzed. Positive impacts of HA on tomato plants grown in hydroponics under osmotic stress were observed on morphological and physiological parameters with an increase of fresh, dry and water weight of aerial and roots parts, plant length and leaf area, as well as a raise of stomatal conductance and total chlorophyll content. The reduction of the malondialdehyde concentration in aerial parts of plants treated with HA reflects a reduction of oxidative stress. The interaction between HA and endophytic bacteria associated to tomato seeds was studied in a second bioassay. Seeds are known to be a major vehicle for PGP bacteria through generations and to maintain a stable community in plants. For this purpose, a sterile culture system in hydroponics was developed. The positive effects of HA were confirmed and the culture in sterile conditions enabled to isolate seed endophytic bacteria, offering new opportunities in studying seed endophytic bacteria–HA interactions