The participation of the cell wall hydrolytic enzymes in the initial colonization of Azospirillum brasilense on wheat roots

Abstract

The effect of cellulase and pectinase on bacterial colonization of wheat was studied by three different experiments. In the first experiment, the root colonization of 3 wheat cultivars (Ghods, Roshan and Omid) by two A. brasilense strains (Sp7 and Dol) was compared using pretreated roots with cellulase and pectinase, and non-treated with these enzymes (control). Although the root colonization varied greatly among strain-plant combinations in controls, the pre-treatment of roots with polysaccharide degrading enzymes significantly increased the bacterial count in roots, regardless of the strainplant combination. This might be an indication that cell wall may act as an important factor in plant-Azospirillum interaction. In the second experiment, the root cellulase activity of the same wheat cultivars treated with and without the two Azospirillum brasilense, strains (Sp7 and Dol) was compared. The pre-treatment of wheat roots with Azospirillum enhanced the cellulase activity of wheat root extracts. Thus, the cellulase activity might participate in the initial colonization of wheat roots by Azospirillum. The comparison of the cellulase activity of root extracts within inoculated and non-inoculated seedlings showed that the inoculation had enhanced the cellulase activity in root extracts, but this effect was directly dependent on the strain-plant combination. Strain Sp7 stimulated the highest cellulase activity in cv. Roshan, but strain Dol induced the highest enzyme activity in cv. Ghods. In the third experiment, several growth parameters of those 3 wheat cultivars treated with and without those two bacterial strains (Sp7 and Dol) were compared. The highest magnitude of growth responses caused by Sp7 strain was in the cv Roshan, but Dol strain stimulated the highest growth in cv Ghods. Therefore, effective colonization may contribute to more growth responses.

Accessing inoculation methods of maize and wheat with Azospirillum brasilense

“…Azospirillum colonizes plant niches that are protected from oxygen and, as a result, nitrogenase is maintained functional (Dobbelaere et al 2003 ). Colonization of intercellular spaces between the epidermis and the cortex, and of the outermost layers of the cortex of inoculated roots is frequently observed (Patriquin et al 1983 ; Mostajeran et al 2007 ). A. brasilense was predominantly located between the apoplast and the epidermal cells of wheat roots (Nabti et al 2010 ).…”

Mechanisms and Practical Considerations Involved in Plant Growth Promotion by Rhizobacteria

“…The additive hypothesis proposes the possibility of multiple mechanisms that function simultaneously or sequentially (Bashan and de-Bashan, 2010). In the case of Azospirillum, N fixation has largely been discounted and primary plant growth promotion mechanism is now attributed to several other functions including phytohormones production (Dobbelaere et al, 1999;Malhotra and Srivastava, 2008), ACC deaminase activity (Li et al, 2005) and hydrolytic enzyme production (Mostajeran et al, 2007). Today, it is increasingly recognized that many PGPR strain likely function by more than one mechanism (de Freitas et al, 1997).…”

Calendula officinalis—A Great Source of Plant Growth Promoting Endophytic Bacteria (PGPEB) and Biological Control Agents (BCA)

“…The ability of bacteria to colonize different plant tissues depends on several factors including their ability to move (e.g., swarming motility) towards nutrient-rich environments (chemotaxis), produce surfactants, form strong biofilm and eventually adhere to the application plant-surface [ 78 , 79 , 80 ]. Previous studies have shown that endophytes producing extracellular hydrolytic enzymes are involved in the indirect promotion of plant growth, as the secretion of these enzymes, namely cellulase and pectinase, could help them invade the cell wall, ultimately aiding in the colonization process of their roots [ 81 , 82 , 83 ]. In the present study, the selected B. halototolerans strains (Cal.l.30, Cal.f4, Cal.l.11, Cal.r.11., Cal.f.2.1), B. subtilis Cal.r19 and B. velezensis Cal.r29 performed the most extensive swarming, swimming and chemotactic motility in vitro and successfully colonized tomato seedlings’ root surface and the detached tomato fruits by creating a visible biofilm in the wound, thus protecting the fruits from the post-harvest pathogen B. cinerea .…”