Interactions between Pseudomonas putida UW4 and Gigaspora rosea BEG9 and their consequences for the growth of cucumber under salt-stress conditions

Abstract

Aims: After the determination of the toxic but nonlethal concentration of NaCl for cucumber, we examined the interaction between an ACC (1‐aminocyclopropane‐1‐carboxylate) deaminase producing bacterial strain and an arbuscular mycorrhizal fungus (AMF) and their effects on cucumber growth under salinity. Methods and Results: In the first experiment, cucumber seedlings were exposed to 0·1, 50, 100 or 200 mmol l−1 NaCl, and plant biomass and leaf area were measured. While seeds exposed to 200 mmol l−1 NaCl did not germinate, plant growth and leaf size were reduced by 50 or 100 mmol l−1 salt. The latter salt cancentration caused plant death in 1 month. In the second experiment, seeds were inoculated with the ACC deaminase‐producing strain Pseudomonas putida UW4 (AcdS+), its mutant unable to produce the enzyme (AcdS−), or the AMF Gigaspora rosea BEG9, individually or in combination and exposed to 75 mmol l−1 salt. Plant morphometric and root architectural parameters, mycorrhizal and bacterial colonization and the influence of each micro‐organism on the photosynthetic efficiency were evaluated. The AcdS+ strain or the AMF, inoculated alone, increased plant growth, affected root architecture and improved photosynthetic activity. Mycorrhizal colonization was inhibited by each bacterial strain. Conclusions: Salinity negatively affects cucumber growth and health, but root colonization by ACC deaminase‐producing bacteria or arbuscular mycorrhizal fungi can improve plant tolerance to such stressful condition. Significance and Impact of the Study: Arbuscular mycorrhizal fungus and bacterial ACC deaminase may ameliorate plant growth under stressful conditions. It was previously shown that, under optimal growth conditions, Ps. putida UW4 AcdS+ increases root colonization by Gi. rosea resulting in synergistic effects on cucumber growth. These results suggest that while in optimal conditions ACC deaminase is mainly involved in the bacteria/fungus interactions, while under stressful conditions this enzyme plays a role in plant/bacterium interactions. This finding is relevant from an ecological and an applicative point of view.

Evidence for the involvement of ACC deaminase from Pseudomonas putida UW4 in the biocontrol of pine wilt disease caused by Bursaphelenchus xylophilus

“…While P. putida UW4 was able to decrease crown gall formation and subsequent damage and loss of plant biomass, the acdS knockout mutant had no significant impact on protecting tomato plants from the A. tumefaciens infection (Hao et al 2007;Toklikishvili et al 2010). These results suggest that ACC deaminase activity, and the consequent lowering of deleterious plant ethylene levels, is the mechanism responsible for P. putida UW4 plant growth promotion activity as well as its ability to protect plants against biotic as well as abiotic stress (Grichko et al 2000;Wang et al 2000;Cheng et al 2007;Glick et al 2007;Hao et al 2007;Gamalero et al 2010;Toklikishvili et al 2010). In addition, it has been previously demonstrated that transgenic plants that express a bacterial acdS gene under the control of a root specific promoter are more resistant to pathogen induced stress as well as abiotic stress caused by salt, flooding and metals (Robison et al 2001a, b;Grichko and Glick 2001;Grichko et al 2000;Stearns et al 2005;Sergeeva et al 2006).…”

“…Synergistic interactions between P. putida UW4 and the arbuscular mycorrhizal fungus Gigaspora rosea, that positively affected cucumber plant growth, have been described (Gamalero et al 2008(Gamalero et al , 2010.…”

“…This enzyme cleaves the ethylene precursor, ACC, into ammonia and a-ketobutyrate (Honma and Shimomura 1978) and thereby prevents ethylene levels in plants from rising to deleterious levels (Glick et al 1998. The ACC deaminase-producing bacterium Pseudomonas putida UW4 has been shown to be an effective PGPB protecting several different plant hosts from a variety of stress conditions including flooding, salt, pathogens and metals (Grichko et al 2000;Wang et al 2000;Grichko and Glick 2001;Cheng et al 2007;Hao et al 2007;Gamalero et al 2010;Toklikishvili et al 2010).…”

Prospects for the use of multi-component symbiotic systems of the Legumes

“…The AM also plays an important role in carbon and nitrogen recycling (Pattinson et al, 2004;Siddiqui et al, 2008;Smith, Read, 2008). In addition, mycorrhized plants have increased resistance to biotic and abiotic stresses (Babikova et al, 2013;Bennett et al, 2009;Bothe, 2012;Campanelli et al, 2013;Currie et al, 2011;Gamalero et al, 2009Gamalero et al, , 2010Kempel et al, 2010;Koltai, Kapulnik, 2010;Koricheva et al, 2009;Liu et al, 2007;Siddiqui et al, 2008). The AMF improve soil structure due to release of a glomalin protein by extraradical mycelium (Rillig, 2004;Siddiqu et al, 2008), as well as increase soil fertility (Celik et al, 2004;Mäder et al, 2011).…”

Inducing salinity tolerance in chickpea (Cicer arietinum L.) by inoculation of 1-aminocyclopropane-1-carboxylic acid deaminase-containing Mesorhizobium strains

“…Recently, plants inoculated with plant growth promoting rhizobactertia containing ACC deaminase activity have been found to thrive through the salinity menace leading to normal growth pattern (Mayak et al, 2004a;Saravanakumar and Samiyappan, 2006;Gamalero et al, 2010). Mayak et al (2004b) reported that inoculation with rhizobacterial strains dramatically lowered the level of ethylene and growth inhibition of tomato plants was prevented when grown in the presence of high concentration of salts.…”