ABSTRACISince 14malonylamino)cyclopropane-l-carboxylic acid (MACC), the major conjugate of 1-aminocyclopropane-l-carboxylic acid (ACC) in plant tissues, is a poor ethylene producer, it is generally thought that MACC is a biologically inactive end product of ACC. In the present study we ACC2 is the immediate precursor of ethylene, which is synthesized via the following sequence in higher plants: Methionine -* SAM --+ ACC --ethylene (1, 24). In addition to serving as a precursor for ethylene, ACC can also be widely metabolized to the stable conjugate, MACC (3,6,7,11,13,16,19,22,23). This conversion is thought to participate in the regulation of ethylene biosynthesis by removing excess ACC (24). Since MACC is a poor ethylene precursor and the conjugation of ACC to MACC is essentially irreversible, MACC is generally thought to be a biologically inactive end product of ACC rather than a storage pool for ACC and hence for ethylene (3,7,8,25). MACC was found to accumulate when high rates of ACC synthesis were induced by water deficit (8) or other factors (3,6,20,23). However, a decrease in MACC content was reported so far only in two systems: in the second node of pea plants (6) (15). Seedling leaves from various ages were used. In one experiment leaf discs from lettuce (Lactuca sativa L.) and soybean (Glycine max L.), root segments of radish (Raphanus sativus L.) and carrot (Daucus carota L.) and fruit plugs of banana (Musa acuminata Colla) and chinese gooseberry (Actinidia chinensis) were used. All fruits and vegetables were purchased from local market.

When whole unripe green tomato fruits (Lycopersiconescukntum Mill, cv T3) were treated with ethylene (10 microliters per liter) for 18 hours, the fruit's ability to convert 1-aminocyclopropane-l-carboxylic acid (ACC) to N-malonyl-ACC (MACC) increased markedly and such an effect was also observed in fruits of mutant nor, which cannot ripen normally. The (5 nmol, 190 nCi). Two discs from each treatment were incubated in an Erlenmeyer flask for 6 h. After incubation, the discs were rinsed with water and extracted with 80% ethanol. The extract was concentrated under reduced pressure and the radioactive metabolites were separated by paper chromatography using 1-butanol:acetic acid:water (4:1:1.5, v/v) as the developing solvent. The radioactivities in paper chromatograms were determined with a radioscanner. For quantitative determination of radioactive amino acid conjugates, the tissues were extracted with ethanol and, after removal of ethanol, the extract was passed through an ion exchange resin column of Dowex 50 (H' form) as described previously (17). The radioactivities in the extract and in the effluent were taken as the total extractable radioactivity and conjugate radioactivity, respectively. Radioactivity was determined with a scintillation counter.Assay of Malonyltransferase Activity. The extraction and determination of the malonyltransferase were essentially those described by Kionka and Amrhein (14) The radioactivity in the reaction mixture and the radioactivity in the effluent plus washing were taken as the amount ofsubstrate and product (MACC), respectively. The enzyme activity was expressed as nmol MACC formed/mg protein -h. RESULTSPromotion of MACC Formation by Ethylene. Table I shows that pretreatment with ethylene resulted in little change in ethylene production of the discs, although the discs prepared from normal tomato cv T3 produced higher ethylene than those from the mutant nor. Ethylene treatment, however, resulted in lower ACC levels in both cultivars, but exerted little changes in MACC levels, which ranged between 1.2 and 1.9 nmol g7'. When ACC was administered to discs prepared from air-treated fruits, the MACC level increased only slightly (about 2 nmol g-') during the 6-h incubation period. This increase represented less than I% of ACC within the tissues, indicating that the capability to convert ACC to MACC in those preclimacteric tomato fruit tissues was as low as their capability to convert ACC to ethylene (18; Table I). The exogenous ethylene treatment promoted the tissues' capability to convert ACC to MACC more than 10-fold in both cultivars, although the magnitude of the promotion varied among different experiments. In parallel with the increase in MACC formation, the capability to convert ACC to ethylene also increased by ethylene treatment (18). Since CHI was present in the incubation solution, it can be assumed that there was little new synthesis of enzymes in the discs during the incubation period as observed by other investigators (5,9,30). Moreover, the quantity of ...

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1-Aminocyclopropane-1-carboxylic acid (ACC) is known to be converted to ethylene and conjugated into N-malonyl-ACC in plant tissues. When α-amino[1-(14)C]isobutyric acid (AIB), a structural analog of ACC, was administered to mungbean (Vigna radiata L.) hypocotyl segments, it was metabolized to (14)CO2 and conjugated to N-malonyl-AIB (MAIB). α-Aminoisobutyric acid inhibited the conversion of ACC to ethylene and also inhibited, to a lesser extent, N-malonylation of ACC and D-amino acids. Although the malonylation of AIB was strongly inhibited by ACC as well as by D-amino acids, the metabolism of AIB to CO2 was inhibited only by ACC but not by D-amino acids. Inhibitors of ACC conversion to ethylene such as anaerobiosis, 2,4-dinitrophenol and Co(2+), similarly inhibited the conversion of AIB to CO2. These results indicate that the malonyalation of AIB to MAIB is intimately related to the malonylation of ACC and D-amino acids, whereas oxidative decarboxylation of AIB is related to the oxidative degradation of ACC to ethylene.

Nlcotana gluUnosa compensated for a mutated tumor-morphology-shooty (tms) (auxin biosynthesis) locus of Agrobacterium tumefaclens strain A66 and showed the same virulent tumor response to infection by strain A66 or the wild-type strain A6. Cloned cell lines transformed by strains AS or A66 were fully hormone independent in culture and grew rapidly as friable, unorganized tissues on hormone-free growth medium. Growth of N. glutinosa tumor cells was inhibited by additon of a-naphthaleneacetic acid to the growth medium, and AS-and A66-transformed cells showed similar dose responses to this auxin. On the other hand, A6-transformed cells contained much higher levels of indole-3-acetic acid (IAA) and 1-aminocyclopropane-1-carboxylic acid (ACC) than A66-transformed cells.

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