Inhibition of Auxin-Induced Ethylene Production by Lycoricidinol

Lycoricidinol, a natural growth inhibitor isolated from bulbsof Lycoris radiata Herb. strongly suppressed auxin-induced ethyleneproduction from the hypocotyl segments of etiolated mung bean(Vigna radiata Wilczek) seedlings. The inhibitor did not significantlyinhibit ethylene formation from its immediate precursor, 1-aminocyclopropane-1-carboxylicacid (ACG), during short-term (up to 4 h) incubation. The ACCcontent in tissue treated with IAA was reduced by lycoricidinolin close parallel with the inhibition of ethylene production.Examination of radioactive metabolites in tissues labeled with3,4-¹⁴C-methionine indicated that reduction of the ACC contentwas not due to any possible promotive effect of lycoricidinolon conjugation of ACC with malonate. Lycoricidinol showed noinhibitory effect on the activity of ACC synthase if appliedin vitro, but it almost completely abolished the increase inthe enzyme activity when applied in vivo during incubation ofthe tissue with IAA. Lycoricidinol also strongly inhibited incorporationof ¹⁴C-leucine into protein in the tissue. The suppression ofthe enzyme induction and, in turn, that, of ethylene productionby lycoricidinol were interpreted as being due to the inhibitionof protein synthesis. (Received September 30, 1983; Accepted December 8, 1983)     

Immunochemical Difference of Wound-Induced 1-Aminocyclopropane-1-carboxylate Synthase from the Auxin-Induced Enzyme

Immunochemical cross-reactivity of wound- and auxin-induced1-aminocyclopropane-1-carboxylate (ACC) synthase was examinedwith the antibody against wound-induced ACC synthase purifiedfrom mesocarp of winter squash (Cucurbita maxima Duch.). Theantibody recognized ACC synthase from wounded hypocotyls ofwinter squash and from wounded pericarp of tomato fruits, butnot the enzyme from IAA-treated hypocotyls of winter squash,tomato and mung bean. These results indicate that the primarystructure of the wound-induced enzyme is different from thatof the auxin-induced enzyme in the same species, and impliesthat there are two different genes for ACC synthase, one forwound induction and the other for auxin induction. (Received June 14, 1988; Accepted July 20, 1988)     

Monomeric and Dimeric Forms and the Mechanism-Based Inactivation of 1-Aminocyclopropane-1-Carboxylate Synthase

The molecular mass of 1-aminocyclopropane-1-carboxylate (ACC)synthase from a variety of sources was examined by both high-performancegel-filtration chromatography and polyacryl-amide gel electrophoresisin the presence of sodium dodecylsulfate. Enzymes used wereprepared from wounded or non-wounded pericarp of ripe tomatofruits and wounded mesocarp of winter squash fruits, as wellas from cells of E. coli that had been transformed with cDNAsfor the wound-induced or ripening-induced ACC synthases of tomatoand the wound-induced or auxininduced enzymes from winter squash.The enzymes from tomato fruit tissues were isolated in a monomericform, whereas the enzymes synthesized in E. coli from cDNAsfor tomato ACC synthase were isolated in a dimeric form. ACCsynthases of winter squash obtained either from fruit tissuesor from transformed E. coli cells were isolated in dimeric forms.ACC synthase in the monomeric form was less sensitive to theinactivation that is associated with the catalytic reaction(the mechanism-based inactivation) than the enzyme in the dimericform. A plausible mechanism relating the difference in molecularform to sensitivity to the mechanism-based inactivation of tomatoACC synthase is discussed. (Received February 1, 1993; Accepted May 17, 1993)     

Characterization of a monoclonal antibody, HTA28, recognizing a histone H3 phosphorylation site as a useful marker of M-phase cells.

Mitosis is a valuable indicator of active tissue proliferation but, other than morphological characteristics, there have hitherto been no markers available to detect only M-phase cells. However, a newly established monoclonal antibody (MAb), HTA28, recognizing histone H3 (H3) harboring phosphoserine 28, allows visualization with mitotic chromosomal condensation. In this study we investigated the use of HTA28 for immunohistochemical (IHC) detection of M-phase cells in the regenerating rat liver after partial hepatectomy (PH). Groups of three to five rats were sacrificed at intervals up to 72 hr after PH and proliferation was then assessed by IHC staining using HTA28 and other markers. The temporal pattern of the HTA28 staining index (SI) was very similar to that for the mitotic index (MI), also showing similarities to the bromodeoxyuridine (BrdU) labeling index (LI) with a time lag. The HTA28 SI proved to be higher than MI at every time point in line with HTA28 immunoreactivity maintained for all stages of M-phase. The spatial distribution of HTA28-positive cells corresponded with those of other proliferative cell markers. These therefore provide strong evidence for the applicability of HTA28 as an M-phase marker. We also showed that antigenicity for HTA28 is lost if tissue is not immediately fixed after sampling.     

Studies on enzymes involved in DNA synthesis and thymine nucleotide formation in potato tuber slices

Activity changes of several enzymes involved in DNA synthesiswere investigated in potato tuber tissue in which DNA synthesiswas induced by slicing. Nucleoside phosphotransferase activityincreased only slightly during aging of the tissue discs. Thymidinemonophosphate (TMP) kinase activity increased about 36% afteraging for 24 hr. Protein synthesis in an early stage of agingwas necessary for the activity increase. A 2.7-fold increasewas observed in DNA polymerase activity after aging for 36 hr.The activity increase was due to continuous synthesis of enzymeprotein. In vivo examination of TMP synthetase suggests thatits activity does not necessarily increase before full developmentof DNA synthesis. It was concluded that among the enzymes examined,TMP kinase activity may increase shortly after slicing to supporta massive supply of thymidine triphosphate and the increasedactivity of DNA polymerase may contribute to the active synthesisof DNA in aged discs. (Received February 18, 1977; )