Developmental Formation of Glutamine Synthetase in Greening Pumpkin Cotyledons and Its Subcellular Localization

Nishimura, Mikio; Bhusawang, Parichart; Strzałka, Kazimierz; Akazawa, Takashi

doi:10.1104/pp.70.2.353

Cited by 28 publications

(12 citation statements)

References 15 publications

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“…The accumulation of GS2 has been shown to be coupled with the development of chloroplasts; GS, activity predominated in etiolated rice leaves (6,8), pumpkin cotyledons (17), and bean leaves (13), but decreased during greening while GS2 activity increased to a much higher level than GS, when greening was completed. In the present study, we have shown that the level of translatable mRNA for GS2 is positively regulated by light, but that for GS, is independent from light conditions in green radish cotyledons.…”

Section: Discussionmentioning

confidence: 99%

“…Root nodules of legumes contain another type of enzyme, nodule-specific GS. The accumulation of these isoforms are differentially regulated; the GS2 activity has been shown to increase during the greening of etiolated plants (8,17), and increase in the activity of nodulespecific GS in developing nodules has been shown to accompany the accumulation of its mRNA (5). ' City University, Mutsukawa, Minami-ku, Yokohama 232, Japan.…”

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Senescence-Specific Increase in Cytosolic Glutamine Synthetase and Its mRNA in Radish Cotyledons

Kawakami¹,

Watanabe²

1988

Plant Physiol.

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Changes in the levels of cytosolic and chloroplastic isoforms of glutamine synthetase were examined in senescing radish (Raphanus sativus L. cv Comet) cotyledons by immunoblotting analysis using antibodies raised separately against maize glutamine synthetase isoforms. Translatable mRNAs for these isoforms were also examined by analyzing translation products from poly(A)' RNA in a wheat germ system with the antibodies. The relative content of cytosolic isoform (GS,) increased twofold in the cotyledons that were placed in the dark for 72 hours to accelerate senescence, while that of chloroplastic isoform (GS2) declined to half of its initial level. The dark-treatment also increased the relative level of translatable mRNA for GS, sevenfold after 72 hours, and decreased rapidly that for GS2 and for other nuclear-coded chloroplast proteins as well. Cotyledons also accumulated GS, mRNA when they became senescent after a lengthy growth period under continuous light. These observations suggested that GS, genes were activated, while those for GS2 were repressed, and eventually the population of the enzyme was altered in senescent cotyledonary cells. The role of increased cytosolic enzyme is discussed in relation to the nitrogen metabolism in senescent leaves.Glutamine synthetase plays a central role in nitrogen metabolism of higher plants. It is responsible for the primary assimilation of ammonia in root cells, and for that of ammonia generated by nitrite reduction in chloroplasts. It also works in the assimilation of ammonia produced by nitrogen fixation in root nodules, and in the reassimilation of ammonia released by photorespiration in the leaf cells (14). In many plant species leaf cells contain two isoforms of GS,3 one in the cytosol (GS,) and the other in the chloroplast (GS2). Root nodules of legumes contain another type of enzyme, nodule-specific GS. The accumulation of these isoforms are differentially regulated; the GS2 activity has been shown to increase during the greening of etiolated plants (8,17), and increase in the activity of nodulespecific GS in developing nodules has been shown to accompany the accumulation of its mRNA (5).

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Section: Discussionmentioning

confidence: 99%

mentioning

confidence: 99%

Senescence-Specific Increase in Cytosolic Glutamine Synthetase and Its mRNA in Radish Cotyledons

Kawakami¹,

Watanabe²

1988

Plant Physiol.

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“…MATERIALS AND METHODS Plant growth condition was described previously (9). Pumpkin cotyledons grown under the three different conditions described in "Results and Discussion" were harvested and sliced (1 mm thick) with a razor blade.…”

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Immunocytochemical Analysis Shows that Glyoxysomes Are Directly Transformed to Leaf Peroxisomes during Greening of Pumpkin Cotyledons

Nishimura¹,

Yamaguchi²,

Mori³

et al. 1986

Plant Physiol.

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The functional transition of glyoxysomes to leaf peroxisomes occurs during greening of germinating pumpkin cotyledons (Cucurbita sp.Amakuri Nankin). The immunocytochemical protein A-gold method was employed in the analysis of the transition using glyoxysomal specific citrate synthase immunoglobulin G and leaf peroxisomal specific glycolate oxidase immunoglobulin G. The labeling density of citrate synthase was decreased in the microbodies during the greening, whereas that of glycolate oxidase was dramatically increased. Double labeling experiments using different sizes of protein A-gold particles show that both the glyoxysomal and the leaf peroxisomal enzymes coexist in the microbody of the transitional stage indicating that glyoxysomes are directly transformed to leaf peroxisomes during greening.There exist two functionally different types of microbody in plant tissues. Glyoxysomes are unique organelles engaged in the degradation of reserve oil via #-oxidation and glyoxylate cycle in germinated fatty seeds such as pumpkin (Cucurbita sp.) (1, 5). Upon greening, the cotyledons become photosynthetic organs; functional leaf peroxisomes, with a crucial role in photorespiration, appear together with chloroplasts. The important question is raised of whether the functional transition of microbodies proceeds in a linear and continuous fashion or whether a discontinuous, two-step sequence operates therein. Indeed, two drastically opposing hypotheses, i.e. 'one-population' and 'two-population' models, have been proposed (1). According to the onepopulation hypothesis, glyoxysomes are directly transformed to leaf peroxisomes during greening of cotyledons, accompanying the insertion of newly synthesized leaf peroxisome-specific enzymes and the concomitant breakdown of glyoxysome-specific enzymes (2, 12). On the contrary, the two-population hypothesis postulates that glyoxysomes are broken down and leaf peroxisomes are newly synthesized de novo (6, 7). As schematically illustrated in Figure 1, according to the one-population hypoth-

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“…The enzyme plays important roles in nitrogen assimilation in bacteria and plants. In plants, GS is produced by de novo synthesis in chlorophyl 44), 45) coupled with photorespiration, 46) in order to prevent the harmful accumulation of generated ammonia by assimilation (Fig. 6).…”

Section: )-14)mentioning

confidence: 99%

Cell-based screening strategy in the search for bioactive microbial secondary metabolites

Iwasaki

Ōmura

2004

Proceedings of the Japan Academy. Ser. B: Physical and Biologic

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(Contributed by Satoshi 1MURA, M. J. A., Feb. 12, 2004) Abstract: Here we present results obtained in our group from cell-based screenings of microbial secondary metabolites using intact microbial and mammalian cells having specific functions. We present summaries of the following five categories of compounds and the strategies that were used to identify them. (1) Antibacterial agents targeting cell wall peptidoglycan synthesis as well as active agents against organisms other than bacteria were identified by a combination of Bacillus subtilis and Mycoplasma as test organisms. (2) Antimetabolites, such as herbicidal agents targeting glutamine synthase, were identified using B. subtilis grown on minimal medium with or without the addition of glutamine and folate inhibitors by combination of B. subtilis and Enterococcus faecium, which have distinct folate metabolic pathways. (3) Among inhibitors of lipid metabolism, acyl-CoA synthetase inhibitors were identified using two mutants of C. lipolytica with different deletion sites in the fatty acid metabolic pathways, HMG-CoA synthase inhibitors were identified using Vero cells cultured in the presence and absence of mevalonate, and anti-atherosclerosis agents were identified using macrophages. (4) IL-6 inhibitors were detected by a combination of IL-6-dependent and independent murine hybridoma MH60 cells, and (5) Small molecules with TNF-like activities were identified using a mouse neuroblastoma cell line. Some advantages of such screening method and the significance of the identified compounds are discussed.

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Developmental Formation of Glutamine Synthetase in Greening Pumpkin Cotyledons and Its Subcellular Localization

Cited by 28 publications

References 15 publications

Senescence-Specific Increase in Cytosolic Glutamine Synthetase and Its mRNA in Radish Cotyledons

Senescence-Specific Increase in Cytosolic Glutamine Synthetase and Its mRNA in Radish Cotyledons

Immunocytochemical Analysis Shows that Glyoxysomes Are Directly Transformed to Leaf Peroxisomes during Greening of Pumpkin Cotyledons

Cell-based screening strategy in the search for bioactive microbial secondary metabolites

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