A genomic DNA fragment from Desulfovibrio fructosovorans, which strongly hybridized with the hydAB genes from Desulfovibrio vulgaris Hildenborough, was cloned and sequenced. This fragment was found to contain four genes, named hndA, hndB, hndC, and hndD. Analysis of the sequence homologies indicated that HndA shows 29, 21, and 26% identity with the 24-kDa subunit from Bos taurus complex I, the 25-kDa subunit from Paracoccus denitrificans NADH dehydrogenase type I, and the N-terminal domain of HoxF subunit of the NAD-reducing hydrogenase from Alcaligenes eutrophus, respectively. HndB does not show any significant homology with any known protein. HndC shows 37 and 33% identity with the C-terminal domain of HoxF and the 51-kDa subunit from B. taurus complex I, respectively, and has the requisite structural features to be able to bind one flavin mononucleotide, one NAD, and three [4Fe-4S] clusters. HndD has 40, 42, and 48% identity with hydrogenase I from Clostridium pasteurianum and HydC and HydA from D. vulgaris Hildenborough, respectively. The 4.5-kb length of the transcripts expressed in D. fructosovorans and in Escherichia coli (pSS13) indicated that all four genes were present on the same transcription unit. The sizes of the four polypeptides were measured by performing heterologous expression of hndABCD in E. coli, using the T7 promoter/polymerase system. The products of hndA, hndB, hndC, and hndD were 18.8, 13.8, 52, and 63.4 kDa, respectively. One hndC deletion mutant, called SM3, was constructed by performing marker exchange mutagenesis. Immunoblotting studies carried out on cell extracts from D. fructosovorans wild-type and SM3 strains, using antibodies directed against HndC, indicated that the 52-kDa protein was recognized in extracts from the wild-type strain only. In soluble extracts from D. fructosovorans wild type, a 10-fold induction of NADP reduction was observed when H 2 was present, but no H 2 -dependent NAD reduction ever occurred. This H 2 -dependent NADP reductase activity disappeared completely in extracts from SM3. These results indicate that the hnd operon actually encodes an NADP-reducing hydrogenase in D. fructosovorans.Hydrogenases (Hyds) are iron-sulfur enzymes which are responsible for the oxidation of molecular hydrogen, as well as for the reduction of protons during molecular hydrogen production. Hyds are key enzymes in the energy metabolism of the sulfate-reducing bacteria belonging to the genus Desulfovibrio, which use oxidized sulfur compounds as their terminal electron acceptors (31). Many Desulfovibrio species can use molecular hydrogen as their sole energy source (2); thus, the hydrogen oxidation which is thought to take place on the periplasmic side of the inner membrane would be involved in the electron transfer across the membrane and the creation of a proton motive force. Alternatively, Desulfovibrio species can grow on lactate or pyruvate, the oxidation of which in the cytoplasm may result in H 2 production (7,15,26 (class 4). This diversity makes the role of these variou...

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R e~u le 29 novembre 1988 COULOMB, C., COULOMB, P. J., SAIMMAIME, I., LIZZI, Y., et POLIAN, C. 1990. CaractCrisation utlrastructurale d'une rCsistance induite par un Cliciteur d'origine fongique chez un cultivar sensible de Piment. Can. J. Bot. 68 : 381-390.Lorsque le systkme racinaire de jeunes plantules de Piment (Capsicum annuum) d'un cultivar sensible est immergC dans une solution Clicitrice issue du milieu de culture du Trichoderma album, une forte induction de rksistance est constatie dans les feuilles infectCes par le Phytophthora capsici. Dans les tissus envahis par le champignon, les cellules h6tes prksentent un aspect normal et dCveloppent des formations pariktales qui ressemblent aux papilles typiques, mais s'en distinguent par la prksence d'une substance d'origine cytoplasmique, laquelle est phagocytCe et dCgradCe conferant B ces enclaves une fonction lytique et une dynamique particulikre. L'intemention du rkticulum endoplasmique et des peroxysomes B un Cventuel processus de detoxification est CvoquCe. La resistance qui apparait sous l'effet de 1'Cliciteur semble programmCe par la mise en place d'un Ctat de reaction gCnCrateur d'une rCponse de dCfense. COULOMB, C., COULOMB, P. J., SAIMMAIME, I., LIZZI, Y., and POLIAN, C. 1990. Caractirisation utlrastructurale d'une resistance induite par un Cliciteur d'origine fongique chez un cultivar sensible de Piment. Can. J. Bot. 68: 381-390.Elicitation of a sensitive sweet pepper (Capsicum annuum) cultivar roots by immersion in the culture medium of Trichoderma album induces resistance in leaves infected by Phytophthora capsici. In infected tissues, host cells are intact and develop wall formations that look like typical wall appositions, but differ from them by the presence of a substance of cytoplasmic origin, which is phagocytized and degraded, confemng a lytic function and unusual dynamics to these structures. The involvement of the endoplasmic reticulum and peroxysomes in eventual detoxification processes is discussed. The resistance induced by this elicitor seems to be programmed by the establishment of a reactive physiological state, which produces the defense response.