A Model For the Lowering of Plant Ethylene Concentrations by Plant Growth-promoting Bacteria

“In addition, a model was formulated wherein the role of this enzyme in the facilitation of plant growth by PGPB was elaborated [98].”

“Direct growth promotion can be through the synthesis of phytohormones [20], N 2 fixation [21], reduction of membrane potential of the roots [22], synthesis of some enzymes (such as ACC deaminase) that modulate the level of plant hormones [23], as well as the solubilization of inorganic phosphate and mineralization of…”

“This enzyme is responsible for lowering the levels of ethylene in the plant by cleaving the plant-produced ethylene precursor 1-aminocyclopropane-1-carboxylate (ACC) to ammonia and 2-oxobutanoate, preventing ethylene signaling (207).”

“For example, transforming the 1-aminocyclopropane-1-carboxylic acid deaminase gene, which directly stimulates plant growth by cleaving the immediate precursor of plant ethylene (64) into P.”

“As a result, ACC levels in the plant are lowered and the ET content is reduced (Glick et al. 1998).”

“…IAA promotes plant rowth per se (Patten and Glick 2002), (ii) ACC deaminase prevents tress ethylene from becoming overly inhibitory of plant growth Glick et al. 1998) and (iii) siderophores help the plants to acquire ufficient iron in the presence of overwhelming amounts of other potentially…”

“In this way, the bacterium acts as a sink for ACC and thus lowers ethylene level in plants, preventing some of the potentially deleterious consequences of high ethylene concentrations (Glick et al. 1998; Steenhooudt and Vanderleyden 2000; Saleem et al. 2007).”

“Ethylene is an inhibitor of root growth especially reducing the primary root length (Glick et al., 1998; Glick, 2005 ).”

“putida GR12-2 to enhance plant growth include the capacity to synthesize siderophores and thereby provide iron for the plant (7), the capacity to lower growth-inhibiting levels of ethylene in plant tissues by production of 1-aminocyclopropane-1-carboxylic acid (ACC) deaminase (16, 21), and the capacity to secrete IAA…”

“A number of PGPR contain the enzyme 1-aminocyclopropane-1-carboxylate (ACC) deaminase (Jacobson et al. 1994, Shah et al. 1997, Glick et al. 1998, Shah et al. 1998) and this enzyme can cleave the plant ethylene precursor ACC, and thereby lower the level of ethylene in a developing or stressed plant.”

“These bacteria may increase 398 plant growth by various mechanisms like reduction in ethylene production under stress, nitrogen 399 fixation and specific enzyme activity (Glick et al., 1998).”

“impair root development and to facilitate the generation of larger roots which enhance seedling survival [108].”

“[120] that PGPR could enhance the growth of plant by suppressing the expression of ethylene.”

“This enzyme converts ACC (the precursor of the stress hormone ethylene) in a-ketobutyrate and ammonia, lowering the ethylene level (inhibitor of root growth) inside the plant because of lack of precursor (Glick et al. 1998; Glick 2005).”

“production of phytohormones and supply of nutrients [138], production of siderophores and other chelating agents [139], specific enzyme activity and N fixation [140], and reduction in ethylene production which encourages root growth [141].”

“The bacteria utilize the ammonia evolved from ACC as a sole nitrogen source and thereby decrease ACC within the plant (Penrose and Glick, 2001) with the concomitant reduction of plant ethylene (Glick et al., 1998; Belimov et al., 2002).”

“Plant growth-promoting bacteria are free-living soil bacteria that can either directly or indirectly facilitate the growth of plants[2,3].”

“…it has been found that a number of plant growth-promoting bacteria contain the enzyme ACC deaminase (Klee and Kishore, 1992; Jacobson et al., 1994; Glick et al., 1995, 1998; Burd et al., 1998; Kaneko et al., 2000; Belimov et al., 2001, 2005; Kaneko et al., 2002; Babalola et al., 2003; Ma et al.,…”

“This data is consistent with the model [13] of how deaminase-containing plant growth-promoting bacteria lower plant ethylene levels and limit stress-caused damage to plants.”

“The results obtained here confirm previous conclusions about the importance of bacterial ACC deaminase in plant growth promotion (Glick et al., 1998), and expanded our knowledge of bacterial metabolism of ACC, since this is the first report showing utilization of ACC by bacteria as an energy source.”

“…detected in the fungus, Penicillium citrinum (Honma, 1993), and in a number of bacterial strains (Klee and Kishore, 1992; Jacobson et al., 1994; Glick et al., 1995; Campbell and Thomson, 1996; Burd et al., 1998; Belimov et al., 2001; Ghosh et al., 2003; Ma et al., 2003) and in the yeast,…”

“By reducing ethylene and facilitating the formation of longer roots, these bacteria may enhance seedling survival during the first few days after sowing (Glick et al. 1998).”

“It was hypothesized that this enzyme, which has no known function in bacteria, might be part of a mechanism used by certain bacteria to stimulate plant growth (Glick et al., 1998).”

“Pre-screening strategies include in vitro screening for known PGP-related activities such as 1-aminocyclopropane-1-carboxylate (ACC) deaminase [31], phosphate solubilization [32], nitrogen fixation [33], or enhancement of plant immune system function [34,35 ,36].”

“An interesting phenomenon is the enhancement of stress tolerance by lowering the ethylene level (Glick, 1998).”

“Glick et al. (1998) postulate that plants release ACC into the rhizosphere, and that this ACC is hydrolyzed by the bacterial ACC deaminase, thereby reducing ET-mediated suppression of root growth.”

“The ACC deaminase acts on ACC, an immediate ethylene precursor in higher plants, degrading this chemical to alphaketobutyrate and ammonium, (Glick et al., 1998; Grichko and Glick, 2001; Mayak et al., 2004).”

“This reduction in the level of ACC in the rhizosphere increases the exudation of ACC by the plant to maintain equilibrium, reducing the potential synthesis of ethylene since ACC is the immediate precursor of this compound in the plant (Glick et al., 1998).”

“Therefore, PGPR in developing or stressed plants could decrease the levels of ethylene, enhance the life of seedlings, and help the plant in the formation of longer roots (Glick et al. 1998).”

“The 2,3-butanediol dehydrogenase ButB (15) involved in the conversion of acetoin into 2,3-butanediol was not found encoded on the genomes of the endophytic bacteria but is present on the poplar genome.”

“…such as reduction of ethylene production (thus allowing plants to develop longer roots and better establish during early stages of growth; see Glick et al., 1998), nitrogen fixation, specific enzymatic activity (Khan, 2005), supply of bioavailable phosphorous and other trace elements for…”

“123 on plants ( Glick et al. 2002 ). The ACC of roots is metabolized by ACC deaminase to ketobutyrate and ammonia (Penrose and Glick 2001).”

“ing plants (21), may further contribute to the heavy metal”

“It was hypothesized that this enzyme, which has no known function in bacteria, might be part of a hitherto undescribed mechanism used by certain bacteria to stimulate plant growth (21).”

“From the previous findings, it has been established that bacteria containing ACC deaminase activity would act to reduce the level of stress ethylene and thus confer resistance to various stresses (Glick et al. 1998).”

“Reduced ACC levels lead to a reduction in the levels of endogenous ET, thus eliminating the inhibitory effect of higher ET concentrations (Glick et al., 1998).”

“The model which represents how a PGPR bound to either a seed or plant root lowers the ethylene concentration and thereby prevents ethylene inhibition of root elongation was previously proposed by Glick et al.(1998).”

“Also in maize and canola, the rhizobacterial treatment increased the total chlorophyll contents (a, b and carotenoids) (Glick et al. 1998; Nadeem et al. 2007).”

“Since a dynamic equilibrium of ACC concentration exists between root, rhizosphere and bacterium, bacterial uptake of rhizospheric ACC (for use as a carbon and nitrogen source) decreases root ACC concentration and root ethylene evolution and can increase root growth in vitro (Glick et al., 1998; Penrose et al., 2001).”

“The enzyme 1aminocyclopropane-1-carboxylate (ACC) deaminase can cleave plant-derived ACC (the immediate biosynthetic precursor of ethylene) and thereby lower ethylene levels in plants (Glick et al. 1998).”

“A model (Glick et al., 1998) suggests that plants exude some ACC from roots or seeds, which is taken up by ACCd-containing bacteria, thus decreasing plant ACC levels and ethylene evolution and thus attenuating ethylene-mediated plant growth inhibition (Burd et al., 1998; Belimov et al., 2001;…”

“…and Vanderleyden 1995, Dodd et al. 2010) or by reducing plant ethylene levels through the bacterial enzyme 1-aminocyclopropane-1-carboxylate (ACC) deaminase, which hydrolyses the ACC (immediate ethylene precursor) into 𝛼-ketobutyrate and ammonia (Honma and Shimomura 1978, Glick et al. 1998).”

“Root colonization by rhizobacteria are expressing an ACC (1- aminocyclopropane-1-carboxylate) -deaminase, which lowers ethylene level under unfavorable conditions and confers resistance to stress, by catalyzing the conversion of ACC into ammonia and aketobutyrate (Glick et al., 1998).”

“On the one hand, the bacteria lower the levels of stress ethylene in the plant, thereby allowing the plant to develop longer roots and thus better establish itself during the early stages of growth (Glick et al., 1998).”

“PGPR are able to promote plant growth via direct or indirect mechanisms, or a combination of both [15, 16].”

“In regard to the homeostasis regulation mechanisms, the ABA production or ACC deaminase activity were confirmed in many isolates, and the current literature has identified a strong relationship between that rhizobacterial capabilities and colonized plant tolerance to salt stress (Cohen et al. 2008; Glick et al. 1998).”

“This cleavage decreases ACC and ET levels in the rhizosphere, which lead to a reduction in endogenous ET levels in plants and subsequently, minimize the inhibitory effect of higher ET concentrations [104].”

“2011), inhibition of plant ethylene synthesis (Glick et al. 1998), as well as increasing availability of nutrients like phosphorus, iron and other micro-elements (Costa and Loper 1994; Rodriguez and Fraga 1999), and growth enhancement by volatile compounds (Kai et al.”

“The (largely bacterial) enzyme ACC deaminase (3.5.99.7) cleaves ACC, the immediate precursor of ethylene in plants, producing ammonia and a-ketobutyrate (Honma and Shimomura, 1978), reducing the amount of ethylene that the plant can synthesize (Glick et al., 1998).”

“(ACC) deaminase which modulates the level of ethylene by hydrolyzing ACC, a precursor of ethylene, in ammoniac and a-ketobutyrate (Glick et al., 1998).”

“991 at P>0.01, n015) (Glick et al. 1998; Belimov et al. 2002).”

“…tendae F4 under different metal interplay a-Aminocyclopropane-1-carboxylic acid deaminase (ACCD) assay is used to determine the ability of bacteria to degrade plant ACC, the precursor of ethylene, thereby lowering stress ethylene levels which otherwise affect plant growth (Glick et al. 1998).”

“Interestingly, this ACC deaminase has been detected in some plant growth-promoting bacteria (PGPR), and thus regulates the biosynthesis of ethylene in inoculated plant roots (Glick et al., 1998; Glick, 2005).”

“Recently, inoculation with specific bacteria has been shown to alter the endogenous levels of ethylene, which subsequently led to changes in the growth and development of inoculated plants (Glick et al. 1998).”

“…the amount of ACC, and consequently that of ethylene, therefore reducing the potentially inhibitory effects of higher ethylene concentrations (Glick et al., 1998), feature of extreme importance when plants are exposed to stressful conditions such as heavymetals contamination of the soil…”

“…e-mail: gabdala@exa.unrc.edu.ar D. Alvarez Instituto Nacional de Tecnología Agropecuaria, INTA-EEA Manfredi, Buenos Aires, Argentina 1-carboxylate (ACC) deaminase acts to reduce ethylene level, which is increased by various stresses, and thus confers resistance to stress (Glick et al. 1998).”

“PGPRs contain an enzyme, 1-aminocyclopropane-1-carboxylate (ACC) deaminase, that catalyzes the cleavage of ACC, which is the precursor of ethylene, and as a result, the endogenous ethylene concentration in plants is reduced (Glick et al., 1998).”