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  • 1
    Electronic Resource
    Electronic Resource
    Copenhagen : Munksgaard International Publishers
    Physiologia plantarum 108 (2000), S. 0 
    ISSN: 1399-3054
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Citrus fruits are characterized by the accumulation of high levels of citric acid in the juice sac cells and a decline in acid level toward maturation. It has been suggested that changes in mitochondrial aconitase (EC 4.2.1.3) activity affect fruit acidity. Recently, a cytosolic aconitase (cyt-Aco) homologous to mammalian iron-regulated proteins was identified in plants, leading us to re-evaluate the role of aconitase in acid accumulation. Aconitase activity was studied in 2 contrasting citrus varieties, sweet lime (Citrus limettioides Tan., low acid) and sour lemon (Citrus limon var. Eureka, high acid). Two aconitase isozymes were detected. One declined early in sour lemon fruit development, but was constant throughout sweet lime fruit development. Its reduction in sour lemon was associated with a decrease in aconitase activity in the mitochondrial fraction. Another isozyme was detected in sour lemon toward maturation, and was associated with an increase in aconitase activity in the soluble fraction, suggesting a cytosolic localization. The cyt-Aco was cloned from lemon juice sac cells, but in contrast to the changes in isozyme activity, its expression was constant during fruit development. We present a model, which suggests that reduction of the mitochondrial aconitase activity plays a role in acid accumulation, while an increase in the cyt-Aco activity reduces acid level toward fruit maturation.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1573-5028
    Keywords: Arabidopsis ; jasmonic acid ; soybean ; vegetative storage protein
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The soybean vegetative storage proteins, VSPα and VSPβ, are acid phosphatases that accumulate to very high levels in hypocotyls, young leaves and flowers and pods. The genes encoding the soybean VSP are activated by jasmonate, wounding, sugars and light and down regulated by phosphate and auxin. In this study, expression of an Arabidopsis thaliana gene (Atvsp) encoding a protein homologous to soybean Vspα and Vspβ, was examined and compared to expression of the soybean Vsp genes. Atvsp mRNA was present at high levels in flowers and buds and at low levels in roots, stems, leaves and siliques. Expression of Atvsp in leaves could be induced by wounding or by treatment of illuminated plants with methyl jasmonate and sucrose. Roots of plants with wounded leaves also accumulated Atvsp mRNA indicating that this gene can be regulated by a transmissible wound signal. Phosphate partially inhibited expression of Atvsp. Arabidopsis proteins of 29 and 30 kDa crossreacted with antibodies against soybean VSP. These proteins were very abundant in flowers and the proteins accumulated in leaves and roots of plants treated with methyl jasmonate. The level of these proteins in flowers was similar to the levels of soybean VSP in young soybean leaves. Overall, these data indicate that Arabidopsis Atvsp and soybean VspA/B genes are regulated similarly and that in both plants, the gene products can accumulate to high levels. This suggests that genes homologous to VspA/B may be of greater general significance than previously recognized.
    Type of Medium: Electronic Resource
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  • 3
    ISSN: 1573-5028
    Keywords: ethylene ; gene expression ; thiamine ; fruit ripening ; Citrus
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Maturing citrus fruit undergo pigment changes which can be enhanced by exogenous ethylene. In order to identify genes induced by ethylene in citrus fruit peel, we cloned the gene c-thi1. mRNA corresponding to c-thi1 increased gradually in the peel during natural fruit maturation and in response to ethylene. GA3 pretreatment reduced the inductive effect of ethylene. Levels of c-thi1 increased also in juice sacs but the effect of ethylene was much less prominent. c-thi1 is homologous to yeast and plant genes encoding for an enzyme belonging to the pathway of thiamine biosynthesis. The data suggest that thiamine is involved in citrus fruit maturation.
    Type of Medium: Electronic Resource
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