Effect of plant growth promoting rhizobacteria containing ACC-deaminase on maize (Zea mays L.) growth under axenic conditions and on nodulation in mung bean (Vigna radiata L.)

Abstract

Aims: This study was conducted to test the hypothesis that the bacterial strains possessing 1‐aminocyclopropane‐1‐carboxylic acid (ACC)‐deaminase activity may also promote growth of inoculated plants and could increase nodulation in legumes upon co‐inoculation with rhizobia. Methods and Results: Several rhizobacteria were isolated from maize rhizosphere through enrichment on ACC as a sole N source. Purified isolates were screened for growth promotion in maize under axenic conditions and for in vitro ACC‐deaminase activity. A significant positive correlation was observed between in vitro ACC‐deaminase activity of bacterial cells and root elongation. None of the isolates produced auxins. Bradyrhizobiumjaponicum produced less amount of auxins but did not carry ACC‐deaminase activity. Results of pot experiment revealed that co‐inoculation with Bradyrhizobium and plant growth promoting rhizobacteria (PGPR) isolates enhanced the nodulation in mung bean compared with inoculation with Bradyrhizobium alone. Conclusions: It is highly expected that inoculation with rhizobacteria containing ACC‐deaminase hydrolysed endogenous ACC into ammonia and α‐ketobutyrate instead of ethylene. Consequently, root and shoot growth as well as nodulation were promoted. Significance and Impact of the Study: The ACC‐deaminase trait could be employed as an efficient tool to screen effective PGPR, which could be successfully used as biofertilizers to increase the growth of inoculated plants as well as nodulation in legumes.

Bacterial biosynthesis of 1-aminocyclopropane-1-caboxylate (ACC) deaminase, a useful trait to elongation and endophytic colonization of the roots of rice under constant flooded conditions

“…It is seemed the utilization ability of ACC was the most mechanism involved in root elongation and endophytic colonization by this isolate. These results are in agreement with the findings of other researchers (Glick et al 1995;Mayak et al 2004;Shaharoona et al 2006). A direct correlation has been found between in vitro bacterial ACC-deaminase activity and root growth (Mayak et al 2004;Shaharoona et al 2006).…”

“…These results are in agreement with the findings of other researchers (Glick et al 1995;Mayak et al 2004;Shaharoona et al 2006). A direct correlation has been found between in vitro bacterial ACC-deaminase activity and root growth (Mayak et al 2004;Shaharoona et al 2006). P. fluorescens strain REN 1 could well promote rice growth and probably by lowering the ACC deaminase activity affected its colonization in rice seedlings.…”

“…Therefore, we assayed this test under constant flooding conditions. A number of studies on PGPR have shown the growth promotion of plant but only under controlled conditions (Glick et al 1995;Shaharoona et al 2006) where these bacteria do not compete with the normal array of microbes. For finding competent isolates in this study, we inoculated all 80 isolates as mixtures of isolates on rice seedling, because competition should possibly imitate the situation in raw soil, which contains approximately 10 8 bacteria g −1 (Lugtenberg and Dekkers 1999).…”

“…Therefore, preferential selection by rice plants of bacteria with high ACC-deaminase activity (instead of those with low or no activity) could confer benefits to the plant. In addition, IAA and ACC deaminase production is being deployed as tools for identification and screening of endophytes (Khalid et al 2005;Shaharoona et al 2006). We identified the best ACC deaminase-producing isolate as Pseudomonas fluorescens.…”

ACC-deaminase and/or nitrogen-fixing rhizobacteria and growth response of tomato (Lycopersicon pimpinellfoliumMill.)

“…This suggested that PGPR isolate that had both ACCdeaminase and N-fixing activities can perform much better than do isolates that had single ability. Shaharoona et al (2006) in a pot experiment revealed that inoculation with PGPR containing ACC-deaminase activity significantly increased the root and shoot growth and fresh and dry weights. It has been reported that certain microorganisms contain an enzyme ACC-deaminase that hydrolyzed the ACC into NH 3 and α-ketobutyrate and reduced the inhibitory effects of ethylene and increased the root-shoot length and fresh and dry weights (Mayak et al 2004).…”