NAD(P)H dehydrogenase (NDH) is a homolog of respiratory complex I and mediates one of the two pathways of cyclic electron flow around PSI (CEF I). Although 15 ndh subunits have been identified in the ...chloroplastic and nuclear genomes of higher plants, no electron accepter subunits have been identified to date. To identify the missing chloroplastic NDH subunits, we undertook an in silico approach based on co-expression analysis. In this report, we characterized the novel gene NDF6 (NDH-dependent flow 6; At1g18730) which encodes a protein that is essential for NDH activity. NDF6 has one transmembrane domain and is localized in the thylakoid membrane fraction. Homologous proteins of NDF6 were identified in the genomes of terrestrial plants; however, no homologs have been found in cyanobacteria, which are thought to be the origin of chloroplasts and have a minimal NDH complex unit. NDF6 is unstable in ndhB-impaired or disrupted mutants of higher plants in which the chloroplastic NDH complex is thought to be degraded. These results suggest that NDF6 is a novel subunit of chloroplastic NDH that was added to terrestrial plants during evolution.
DIMBOA 2,4-dihydroxy-7-methoxy-2H-1,4-benzoxazin-3(4H)-one is a benzoxazinoid (Bx), part of the chemical defense system of graminaceous plants such as maize, wheat, and rye. When Bombyx mori larvae ...were fed artificial diets containing DIMBOA, they died in three days. In contrast, Mythimna separata larvae, a serious pest of rice, maize, sorghum, wheat etc., grew well on the same diets. Three kinds of glucosides 1-(2-hydroxy-4-methoxyphenylamino)-1-deoxy-β-glucopyranoside-1,2-carbamate (methoxy glucoside carbamate), 2-O-β-glucopyranosyl-4-hydroxy-7-methoxy-2H-1,4-benzoxazin-3(4H)-one (DIMBOA-2-O-Glc), and 2-O-β-glucopyranosyl-7-methoxy-2H-1,4-benzoxazin-3(4H)-one (HMBOA-2-O-Glc) were identified by LC-MS and NMR analyses from the frass of M. separata that had been fed on a DIMBOA-containing diet. Furthermore, the incubation of DIMBOA with a midgut tissue suspension of M. separata in the presence of UDP-D-glucose generated DIMBOA-2-O-Glc. These findings strongly suggest that glucosylation by UDP-glucosyltransferase(s) was important for detoxification to circumvent the defenses of host plants against M. separata larvae.
The chloroplast NAD(P)H dehydrogenase (NDH) complex, which reduces plastoquinones in thylakoid membranes, is involved in PSI cyclic electron flow and chlororespiration. In addition to land plants, ...the NDH complex is conserved in cyanobacteria. In this study, we identified a novel NDH-related gene of Arabidopsis, NDH-dependent cyclic electron flow 5 (NDF5, At1g55370). Post-illumination increases in chlorophyll fluorescence were absent in ndf5 mutant plants, which indicated that NDF5 is essential for NDH activity. Sequence analysis did not reveal any known functional motifs in NDF5, but there was some homology in amino acid sequence between NDF5 and NDF2, a known NDH subunit. NDF5 and NDF2 homologs were present in higher plants, but not cyanobacteria. A single homolog, which had similarity to both NDF5 and NDF2, was identified in the moss Physcomitrella patens. Immunoblot analysis showed that NDF5 localizes to membrane fractions of chloroplasts. The stability of NdhH, a subunit of the NDH complex, as well as NDF5 and NDF2, was decreased in ndf5, ndf2 and double ndf2/ndf5 mutants, resulting in a loss of NDH activity in these mutants. These results indicated that both NDF5 and NDF2 have essential functions in the stabilization of the NDH complex. We propose that NDF5 and NDF2 were acquired by land plants during evolution, and that in higher plants both NDF5 and NDF2 are critical to regulate NDH activity and each other's protein stability, as well as the stability of additional NDH subunits.
When mutations in CUP-SHAPED COTYLEDON1 (CUC1) and CUC2 are combined, severe defects involving fusion of sepals and of stamens occur in Arabidopsis flowers. In addition, septa of gynoecia do not fuse ...along the length of the ovaries and many ovules have their growth arrested. CUC2 is expressed at the tips of septal primordia during gynoecium development and at the boundary between nucellus and chalaza during ovule development. These expression patterns are partially consistent with the phenotype of the mutant gynoecium. CUC2 mRNA is also shown to be expressed at the boundaries between meristems and organ primordia during both the vegetative and reproductive phases. This expression pattern indicates that CUC2 is generally involved in organ separation in shoot and floral meristems.
Marine bacteria that kill the noxious red tide flagellate Chattonella antiqua (Raphidophyceae) were screened and isolated from northern Hiroshima Bay, the Seto Inland Sea, Japan in 1991. Four strains ...(S, K, D, R) of Alteromonas spp. were selected and examined on characteristics of algicidal activities. Strains S and R showed wide algicidal range killing all cells of the 3 raphidophycean flagellates, 2 diatoms, and one dinoflagellate examined, in co-culture. Algicidal activities of the strains K and D depend on prey phytoplankton species. Bacterial culture filtrate experiment shows that the bacterial strains K and D give lethal effects on C. antiqua by means of extracellular products, and the strains S and R not by such substances but by predation. If one or two bacterial cells were inoculated into C. antiqua culture, all of the host cells were killed by the 4 strains of algicidal bacteria within 7 days. All of the 4 bacterial strains could proliferate in filter-sterilized seawater, indicating their ubiquitous existence in the coastal sea. We suggest that the algicidal activity by bacteria may be a significant factor influencing the population dynamics of phytoplankton, and potentially might account for rapid termination of red tides in the coastal sea.
Twenty eight strains of the marine bacteria which killed the marine dinoflagellate, Gymnodinium mikimotoi, were isolated during the occurrence of the huge red tide by G. mikimotoi in Tanabe Bay in ...1990. Among them 22 strains belonged to the genus Vibrio, three to Flavobacterium, two to Acinetobacter and one to Pseudomonas-Alteromonas. All of them grew in filter-sterilized natural seawater without any nutrient supplements, suggesting that the killing bacteria are ubiquitous in seawater and are related to the occurrence of G. mikimotoi opportunistically. Most of the killing bacteria did not affect the growth of three marine diatoms, Skeletonema costatum, Ditylum brightwellii and Thalassiosira sp., and some of them did not affect the growth of the marine dinoflagellate, Alexandrium catenella. These findings strongly suggest that the killing bacteria influence the change of microalgal community in a marine environment.
Distribution and seasonal fluctuation of the bacteria which inhibit the growth of a red tide marine dinoflagellate Gymnodinium mikimotoi, were surveyed in Tanabe Bay (Wakayama Pref., Japan), using ...the newly developed MPN method with an axenic culture of G. mikimotoi, G. mikimotoi's growth inhibiting bacteria (Gm-GIB) were detected at 10 super(3)-10 super(4) cells/ml before occurrences of huge red tides by G. mikimotoi at the beginning of August in 1990 and from the end of August to the beginning of September in 1991. The number of Gm-GIB fell by about two orders of magnitude at the blooming periods of G. mikimotoi, and then increased again after the blooms declined. These results suggest that the fluctuation of Gm-GIB counts in seawater is significantly related to the development and decline process of G. mikimotoi red tide. Forty strains of Gm-GIB isolated in this study all acted as killers against this dinoflagellate rather than as suppressers on the algal growth under laboratory conditions. The precise causes of the fluctuation of Gm-GIB in seawater environments remain unknown.
Changes in activities and levels of superoxide dismutase (SOD, EC 1.15.1.1) isoenzymes were studied during air adaptation of submerged rice (Oryza sativa L.) seedlings. Seeds were germinated for 6 d ...in the dark under water (submerged), and then for another day in air (air-adapted). For a control, seeds were germinated for 6 d throughout in air (aerobic). Staining for activity of SOD of shoot extracts showed a total of five major distinct forms of SOD: one mitochondrial Mn enzyme (mtSOD) and four CuZn enzymes, one of which was plastidic (plSOD) and the other three cytosolic (cytSOD). Activity of plSOD was much lower in submerged seedlings than in aerobic controls and increased after exposure to air. In contrast, mtSOD activity in submerged seedlings was as high as that found in aerobic controls, and did not increase upon exposure to air. One of the cytSODs showed responses similar to those of plSOD. The activities of another two cytSODs were slightly lower in submerged seedlings than those in aerobic controls, but decreased after 24 h of air adaptation. Western blot analysis revealed that these changes in activities of SODs are due to changes in the levels of their enzyme proteins. We also followed changes in the levels of cytochrome c and ferredoxin-NADP+ reductase (EC 1.6.99.4) as indices of the development of mitochondria and plastids, respectively. Organelle SODs were always present at higher levels than would be expected in view of the development of the electron-transport systems of the corresponding organelles during submergence and the subsequent air-adaptation period.
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