Ethylene formation from 1-aminocyclopropane-1-carboxylic acid in homogenates of etiolated pea seedlings

109

The rate of C2H, production in plant tissue appears to be limited by the level of endogenous 1-aminocyclopropane-1-carboxylic acid (ACC). Exogenous ACC stimulated C2H4 production considerably in plant tissues, but this required 10 to 100 times the endogenous concentrations of ACC before significant increases in C2H4 production were observed. This was partially due to poor penetration of ACC into the tissues. Conversion of ACC to C2H4 was inhibited by free radical scavengers, reducing agents, and copper chelators, but not by inhibitors of pyridoxal phosphate-mediated reactions. The system for converting ACC to C2H4 may be membrane-associated, for it did not survive treatment with surface-active agents and cold or osmotic shock reduced the capacity of the system to convert ACC to C2H4. The reaction rate was sensitive to temperatures above 29 and below 12 C, which suggests that the system may be associated with membrane-bound lipoproteins. The data presented support the possibility that the conversion of exogenous ACC to C2H4 proceeds via the natural physiological pathway.Considerable evidence has accumulated in the past 14 years to show that C2H4 derives from methionine (10, 1 1). However, until recently, the pathway from methionine to C2H4 remained obscure.The report by Adams and Yang (1) that implicated SAM4 as intermediate between methionine and C2H4 led to their further discovery that the unique amino acid l-aminocyclopropane-lcarboxylic acid is the immediate precursor of C2H4 (2). This discovery established the following biosynthetic sequence for C2H4 production: methionine -* SAM --ACC --C2H4.Knowledge of the intermediates in the biosynthetic pathway to C2H4 has shifted emphasis in this research area to identifying the enzymes and establishing the control and regulation of the reactions involving these intermediates. The enzyme which converts SAM to ACC has recently been shown to be soluble (6,17). However, the enzyme system which converts ACC to C2H4 has not been sufficiently characterized and may be associated with cellular particulates (8,13 4 Abbreviations: SAM, S-adenosyl-L-methionine; ACC, I-aminocyclopropane-l-carboxylic acid; AVG, aminoethoxyvinylglycine.presence of a mercury-catalyzed NaOCl system (12), or simply by reaction with high concentrations of H202 (9). Since there appears to be a number of possible reactions which can convert ACC to C2H2, the question arises as to whether or not, at high concentrations, all ACC exogenously applied to plant tissues is converted to C2H4 by the same enzymic system that utilizes native ACC to form endogenous C2H4. Here, we report some characteristics of the conversion of ACC to C2H4. Plant Material. Apple fruits (Malus sp. Cultivar Golden Delicious) were harvested in the Beltsville orchard at a preclimacteric stage and stored at 0 C until used. Discs 1.0 cm in diameter and 2 mm thick were cut from friits at various stages of ripening. Six discs (1 g) were incubated in a 25-ml Erlenmeyer flask containing 3 ml incubation medium consisting of 600 mm sorbi...

Section: Resultssupporting

confidence: 91%

mentioning

confidence: 99%

Some Characteristics of the System Converting 1-Aminocyclopropane-1-carboxylic Acid to Ethylene

Apelbaum¹,

Burgoon²,

Anderson³

et al. 1981

109

“…This step appears to be associated with a particulate fraction of the cell (7,11). The fact that ethylene production in situ (particularly the ACC-to-ethylene step) is susceptible to osmotic shock (4,12,14), cold shock (4,14), lipophilic membrane perturbants (4,(9)(10)(11)14), and ionic and nonionic detergents (4,1,12,14) indicates involvement of a membrane function in ethylene biosynthesis.…”

Section: Discussionmentioning

confidence: 99%

Polyamines Inhibit Biosynthesis of Ethylene in Higher Plant Tissue and Fruit Protoplasts

Apelbaum¹,

Burgoon²,

Anderson³

et al. 1981

203

Ethylene production in apple fruit and protoplasts and in leaf tissue was inhibited by spermidine or spermine. These (15) during dark-induced senescence of detached leaves. Also, polyamines inhibit development of RNase and protease activity in barley leaf discs (15). The mechanism by which polyamines exert these effects is unknown. These effects, however, are the opposite of those caused by the plant growth regulator, ethylene, which promotes senescence of many plant tissues (8).We investigated the effect of polyamines on ethylene biosynthesis, partly because polyamines and ethylene derive from the same precursor, S-adenosylmethionine (1, 2, 16), and because of the possibility that polyamines regulate plant metabolism by influencing the biosynthesis of ethylene.

“…2) form the beginning (0.5 h) of incubation, the percentage of AVG-inhibitable C2H4 formation is about 6 to 7%, with an eventually slight increase in noninhibitable C2H4 formation by AVG after longer times of incubation. There is good evidence that AVG inhibits the biosynthetic pathway of C2H4 between methionine and ACC (3,16), and that enzymic oxidation of ACC yielding C2H4 is catalyzed by a constitutive enzyme (3,12,15,22). Elicitor treatment seems to enhance synthesis of ACC in soybean cotyledons.…”

Section: C2h4 Formation By Soybean Cotyledons After Elicitor or Accmentioning

confidence: 99%

Ethylene: Indicator but Not Inducer of Phytoalexin Synthesis in Soybean

Paradies

Konze²,

Elstner³

et al. 1980

Cell wail preparations (elicitors) from Phytophthora megasperma var. sojae increase C2H4 formation, phenylalanine ammonia lyase activity, and glyceollin accumulation in soybean cotyledons within about 1.5, 3, and 6 hours after treatment, respectively. The immediate precursor of C2H4, 1-aminocyclopropane-1-carboxylic acid, stimulates C2H4 formation like the elicitor within 1.5 hours after administration, whereas phenylalanine ammonia lyase activity and glyceollin concentration remain unchanged. Aminoethoxyvinylglycine, a specific inhibitor of C2H4 formation in higher plants, inhibits elicitor-induced C2H4 formation by about 95% but has no effects on phenylalanine ammonia lyase or glyceollin accumulation. It was concluded that C2H4 is a signal accompanying the specific recognition process which finally leads to the induction of phytoalexin formation, but it is not functioning as a link or messenger in the induction sequence of glyceollin accumulation.