Metabolism of 1-Aminocyclopropane-1-carboxylic Acid

257

139

We report the presence of ACC deaminase in Methylobacterium fujisawaense and its lowering of ethylene levels and promotion of root elongation in canola seedlings under gnotobiotic conditions. To test a part of the previous model proposed for ACC deaminase producing bacteria with Methylobacterium, ACC levels and various enzyme activities were monitored in canola. Lower amounts of ACC were present in the tissues of seeds treated with M. fujisawaense strains than in control seeds treated with MgSO(4). Though the increased activities of ACC synthase in the tissue extracts of the treated seedlings might be due to bacterial indole-3-acetic acid, the amount of ACC was reduced due to bacterial ACC deaminase activity. The activities of ACC oxidase, the enzyme catalyzing conversion of ACC to ethylene remained lower in M. fujisawaense treated seedlings. This consequently lowered the ethylene in plants and prevented ethylene inhibition of root elongation. Our results collectively suggest that Methylobacterium commonly found in soils, as well as on the surfaces of leaves, seeds, and in the rhizosphere of a wide variety of plants could be better exploited to promote plant growth.

Section: Acc Deaminase Assaymentioning

confidence: 99%

Regulation of ethylene levels in canola (Brassica campestris) by 1-aminocyclopropane-1-carboxylate deaminase-containing Methylobacterium fujisawaense

Madhaiyan

Prabakaran

Ryu

et al. 2006

257

139

“…To measure the ACCd activity in plant tissues, samples were ground in liquid nitrogen and protein was extracted in a cold buVer containing 0.2 M Tris-HCl (pH 7.2), 2 mM EDTA, 2% polyvinylpyrrolidone, 1 mM 2-mercaptoethanol, and 1 mM phenylmethylsulfonyl Xuoride (DumbroV and Gepstein 1993). The insoluble materials were removed by centrifugation at 16,800 g for 25 min at 4°C, and then assayed for ACCd activity according to Penrose and Glick (2003), modiWed from Honma and Shimomura (1978). Blank consisted of tissue extracts added to reagent in the absence of ACC.…”

Section: Measurement Of Enzyme Activities In Plant Extractsmentioning

confidence: 99%

Characterization of 1-aminocyclopropane-1-carboxylate (ACC) deaminase containing Methylobacterium oryzae and interactions with auxins and ACC regulation of ethylene in canola (Brassica campestris)

Madhaiyan

Prabakaran

2007

120

The possible interaction of the plant hormones auxin and ethylene and the role of 1-aminocyclopropane-1-carboxylate (ACC) deaminase containing bacteria on ethylene production in canola (Brassica campestris) in the presence of inhibitory concentrations of growth regulators were investigated. The effects of auxin (indole-3-acetic acid and 2,4-dichlorophenoxy acetic acid), auxin transport inhibitor 2-(p-chlorophenoxy)-2-methylpropionic acid, ethylene precursor 1-aminocyclopropane-1-carboxylate and ethylene synthesis inhibitor L-alpha-(2-aminoethoxyvinyl)glycine hydrochloride on root elongation were concentration dependent. Exogenous addition of growth regulators influences the enzyme activities of ethylene production and we have presented here evidences that support the hypothesis that inhibitory effects of auxin on root elongation are independent of ethylene. Additionally, we have proved that inoculation of ACC deaminase containing Methylobacterium oryzae sequester ACC exuded from roots and hydrolyze them lowering the concentration of ACC in root exudates. However, the inhibitory actions of exogenous additions of auxins could not be ameliorated by bacterial inoculation that reduces ethylene concentration in canola seedlings.

“…Through a mutualistic relationship with plants, plant growth promoting bacteria which possess the enzyme ACC deaminase can take up some of the plant produced ACC and cleave the cyclopropane ring of ACC into -ketobutyrate and ammonia (Honma and Shimomura 1978). ACC levels within plant tissues are reduced which results in decreased plant endogenous ethylene levels, generally facilitating plant growth.…”

Section: Introductionmentioning

confidence: 99%

“…ACC deaminase binds one pyridoxal phosphate (PLP) molecule at each subunit via a conserved lysine residue. The K m of various ACC deaminases for ACC as the substrate indicates that the enzyme does not bind the substrate with high aYnity; the reported K m values range from 1.5 to 9.2 mM (Honma and Shimomura 1978;Walsh et al 1981;Minami et al 1998;Hontzeas et al 2004). To gain insight into the functioning of this PLP-dependent enzyme, the crystal structures of bacterial (Pseudomonas sp.…”

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

The interconversion of ACC deaminase and d-cysteine desulfhydrase by directed mutagenesis

Todorović

Glick

2008

Progress in DNA sequencing of plant genomes has revealed that, in addition to microorganisms, a number of plants contain genes which share similarity to microbial 1-aminocyclopropane-1-carboxylate (ACC) deaminases. These enzymes cleave ACC, the immediate precursor of ethylene in plants, into ammonia and alpha-ketobutyrate. We therefore sought to isolate putative ACC deaminase cDNAs from tomato plants with the objective of establishing whether the product of this gene is a functional ACC deaminase. In the work reported here, it was demonstrated that the enzyme encoded by the putative ACC deaminase cDNA does not have the ability to break the cyclopropane ring of ACC, but rather it utilizes D: -cysteine as a substrate, and in fact encodes a D: -cysteine desulfhydrase. Kinetic characterization of the tomato enzyme indicates that it is similar to other, previously characterized, D: -cysteine desulfhydrases. Using site-directed mutagenesis, it was shown that altering only two amino acid residues within the predicted active site served to change the enzyme from D: -cysteine desulfhydrase to ACC deaminase. Conversely, by altering two amino acid residues at the same positions within the active site of ACC deaminase from Pseudomonas putida UW4 the enzyme was converted into D: -cysteine desulfhydrase. Therefore, it is possible that a change in these two residues may have occurred in an ancestral protein to result in two different enzymatic activities.