Inhibition by polyamines of macromolecular synthesis and its implication for ethylene production and senescence processes.

Applied diamines and polyamines inhibited the incorporation of radioactively labeled leucine and uridine into trichloroacetic acid-insoluble material in apple (Malus domestica Borkh, cv Golden Delicious) fruit tissue. The inhibitory effect was in general more pronounced with the higher molecular weight amines. Putrescine at 5 millimolar inhibited leucine incorporation by 37% and uridine by 44%. Spermidine and spermine at the same concentration inhibited uridine incorporation by 60%. The polyamines at concentrations between 0.1 and 1.0 millimolar inhibited leucine incorporation by 55 to 90%. The inhibitory effect of 0.1 to 10 millimolar polyamines on dark- and wound-induced senescence or ethylene production, is discussed in the light of interference with macromolecular synthesis.

Polyamines inhibit biosynthesis of ethylene in higher plant tissue and fruit protoplasts.

Ethylene production in apple fruit and protoplasts and in leaf tissue was inhibited by spermidine or spermine. These polyamines, as well as putrescine, inhibited auxin-induced ethylene production and the conversion of methionine and 1-aminocyclopropane-1-carboxylic acid to ethylene. Polyamines were more effective as inhibitors of ethylene synthesis at the early, rather than at the late, stages of fruit ripening. Ca(2+) in the incubation medium reduced the inhibitory effect caused by the amines. A possible mode of action by which polyamines inhibit ethylene production is discussed.

Inhibition of the Conversion of 1-Aminocyclopropane-1-carboxylic Acid to Ethylene by Structural Analogs, Inhibitors of Electron Transfer, Uncouplers of Oxidative Phosphorylation, and Free Radical Scavengers.

Cyclopropane carboxylic acid (CCA) at 1 to 5 millimolar, unlike related cyclopropane ring analogs of 1-aminocyclopropane-1-carboxylic acid (ACC) which were virtually ineffective, inhibited C(2)H(4) production, and this inhibition was nullified by ACC. Inhibition by CCA is not competitive with ACC since there is a decline, rather than an increase, in native endogenous ACC in the presence of CCA. Similarly, short-chain organic acids from acetic to butyric acid and alpha-aminoisobutyric acid inhibited C(2)H(4) production at 1 to 5 millimolar and lowered endogenous ACC levels. These inhibitions, like that of CCA, were overcome with ACC. Inhibitors of electron transfer and oxidative phosphorylation effectively inhibited ACC conversion to C(2)H(4) in pea and apple tissues. The most potent inhibitors were 2,4-dinitrophenol (DNP) and carbonyl cyanide m-chlorophenylhydrazone (CCCP) which virtually eliminated ACC-stimulated C(2)H(4) production in both tissues. Still other inhibitors of the conversion of ACC to C(2)H(4) were putative free radical scavengers which reduced chemiluminescence in the free radical-activated luminol reaction. These inhibitor studies suggest the involvement of a free radical in the reaction sequence which converts ACC to C(2)H(4). Additionally, the potent inhibition of this reaction by uncouplers of oxidative phosphorylation (DNP and CCCP) suggest the involvement of ATP or the necessity for an intact membrane for C(2)H(4) production from ACC. In the latter case, CCCP may be acting as a proton ionophore to destroy the membrane integrity necessary for C(2)H(4) production.

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

The rate of C(2)H(4) production in plant tissue appears to be limited by the level of endogenous 1-aminocyclopropane-1-carboxylic acid (ACC). Exogenous ACC stimulated C(2)H(4) production considerably in plant tissues, but this required 10 to 100 times the endogenous concentrations of ACC before significant increases in C(2)H(4) production were observed. This was partially due to poor penetration of ACC into the tissues. Conversion of ACC to C(2)H(4) 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 C(2)H(4) 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 C(2)H(4). 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 C(2)H(4) proceeds via the natural physiological pathway.