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  • 1
    ISSN: 1432-203X
    Keywords: Key words Cuscuta trifolii ; Somatic embryogenesis ; Plant regeneration ; Parasitic weed
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract  In this paper comparative histological studies of embryo-like structures originating from callus cultures, and zygotic embryos originating from sexual seeds of Cuscuta trifolii are reported. The embryos of somatic cell and zygote origin showed similar morphological and anatomical features, such as a complete lack of cotyledon development and the differentiation of a developmentally unique root primordium specialised for water storage. Based on these findings, the regeneration of C. trifolii from callus cultures is shown to proceed along the pathway of somatic embryogenesis.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1365-3040
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Plants respond to various biotic and abiotic stresses by the specific induction of a certain set of genes. This study involved a search for transcripts induced in alfalfa (Medicago sativa L. bv Verko) upon infection with dodder (Cuscuta trifolii Bab. et Gibs). A 570 bp cDNA, designated PPRG1, was isolated by differential display. Southern blot analysis indicates that PPRG1 is a member of a new small gene family in alfalfa. PPRG1 encodes a putative 19·2 kDa calmodulin-related protein with 59% amino acid homology to the touch-inducible TCH2 gene isolated from Arabidopsis. The level of PPRG1 transcript shows a rapid transient increase to mechanical stimuli such as rain, touch and wounding, to osmotic and salt stresses and to external treatment with the plant hormone abscisic acid. Constantly elevated levels of PPRG1 mRNA can be observed during cold stress, whereas heat treatment does not induce PPRG1 expression. These results implicate roles for Ca2+ and PPRG1 in the transduction of signals from the environment.
    Type of Medium: Electronic Resource
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  • 3
    ISSN: 1617-4623
    Keywords: Rhizobium ; Symbiosis ; Oxygen regulation ; nif genes ; Fix- mutants
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Recently, Fix- mutants of Rhizobium meliloti 41 defective for nifHDK transcription in the bacteroid state have been described. Two of these mutants have been used to identify bacterial genes involved in the regulation of nif gene expression. A nifA::lacZ fusion was introduced into the mutant strains and β-galactosidase activity was assayed in nodule bacteria, as well as in bacteria grown under microaerobic conditions. One of the mutants did not express the nifA gene in symbiosis, suggesting that the gene inactivated by mutation fix-24 is involved in controlling the expression of the nif structural genes via the regulatory gene nifA, The mutation fix-24 also impaired the expression of nifA under microaerobic conditions. These data are in agreement with earlier findings that low oxygen concentration may serve as a signal for nif gene expression in symbiosis. The fix gene marked by the mutation fix-24 might be a positive regulator of nifA expression in R. meliloti 41. The other mutation (fix-25) represented another cluster of fix genes which also affected the expression of nifA. This influence, however, was specific for symbisis. The fix genes (fix-24, fix-25) were localized on the symbiotic megaplasmid pRme41b. The two genes are 10 kb apart from each other and are located at 200 kb downstream of the nif structural genes in R. meliloti 41.
    Type of Medium: Electronic Resource
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