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A mutation in GDP-mannose pyrophosphorylase causes conditional hypersensitivity to ammonium, resulting in Arabidopsis root growth inhibition, altered ammonium metabolism, and hormone homeostasis.

Barth C, Gouzd ZA, Steele HP, Imperio RM - J. Exp. Bot. (2009)

Bottom Line: Since VTC1 encodes a GDP-mannose pyrophosphorylase, an enzyme generating GDP-mannose for AA biosynthesis and protein N-glycosylation, it was also tested whether protein N-glycosylation is affected in vtc1-1.Furthermore, since root development requires the action of a variety of hormones, it was investigated whether hormone homeostasis is linked to NH(4)(+) sensitivity in vtc1-1.Our data suggest that NH(4)(+) hypersensitivity in vtc1-1 is caused by disturbed N-glycosylation and that it is associated with auxin and ethylene homeostasis and/or nitric oxide signalling.

View Article: PubMed Central - PubMed

Affiliation: Department of Biology, West Virginia University, 53 Campus Drive, Morgantown, WV 26506-6507, USA. carina.barth@mail.wvu.edu

ABSTRACT
Ascorbic acid (AA) is an antioxidant fulfilling a multitude of cellular functions. Given its pivotal role in maintaining the rate of cell growth and division in the quiescent centre of the root, it was hypothesized that the AA-deficient Arabidopsis thaliana mutants vtc1-1, vtc2-1, vtc3-1, and vtc4-1 have altered root growth. To test this hypothesis, root development was studied in the wild type and vtc mutants grown on Murashige and Skoog medium. It was discovered, however, that only the vtc1-1 mutant has strongly retarded root growth, while the other vtc mutants exhibit a wild-type root phenotype. It is demonstrated that the short-root phenotype in vtc1-1 is independent of AA deficiency and oxidative stress. Instead, vtc1-1 is conditionally hypersensitive to ammonium (NH(4)(+)). To provide new insights into the mechanism of NH(4)(+) sensitivity in vtc1-1, root development, NH(4)(+) content, glutamine synthetase (GS) activity, glutamate dehydrogenase activity, and glutamine content were assessed in wild-type and vtc1-1 mutant plants grown in the presence and absence of high NH(4)(+) and the GS inhibitor MSO. Since VTC1 encodes a GDP-mannose pyrophosphorylase, an enzyme generating GDP-mannose for AA biosynthesis and protein N-glycosylation, it was also tested whether protein N-glycosylation is affected in vtc1-1. Furthermore, since root development requires the action of a variety of hormones, it was investigated whether hormone homeostasis is linked to NH(4)(+) sensitivity in vtc1-1. Our data suggest that NH(4)(+) hypersensitivity in vtc1-1 is caused by disturbed N-glycosylation and that it is associated with auxin and ethylene homeostasis and/or nitric oxide signalling.

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Effect of various MS media compositions on primary root development in 7-d-old wild type and vtc1-1. (A) Primary root length when plants were grown on increasing strength of MS medium. Results illustrate means ±SE of 9–23 individual seedlings per genotype and treatment. (B) Primary root length of plants grown in the absence of phosphorous (–P), ammonium nitrate (–NH4+, with potassium nitrate still present) and in the absence of all nitrogen (–N, i.e. no potassium nitrate and no ammonium nitrate). Data represent means ±SE of 6–18 replicates. (C) Effect of increasing concentrations of ammonium chloride (NH4Cl) on root growth in plants grown on 1× MS medium lacking ammonium nitrate (–NH4+), but potassium nitrate still present. Mean values ±SE of 44–102 individual seedlings per genotype and treatment are shown. Asterisks indicate significant differences between mutant and wild type. *P <0.05, **P <0.01, ***P <0.001, Student's t test.
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fig3: Effect of various MS media compositions on primary root development in 7-d-old wild type and vtc1-1. (A) Primary root length when plants were grown on increasing strength of MS medium. Results illustrate means ±SE of 9–23 individual seedlings per genotype and treatment. (B) Primary root length of plants grown in the absence of phosphorous (–P), ammonium nitrate (–NH4+, with potassium nitrate still present) and in the absence of all nitrogen (–N, i.e. no potassium nitrate and no ammonium nitrate). Data represent means ±SE of 6–18 replicates. (C) Effect of increasing concentrations of ammonium chloride (NH4Cl) on root growth in plants grown on 1× MS medium lacking ammonium nitrate (–NH4+), but potassium nitrate still present. Mean values ±SE of 44–102 individual seedlings per genotype and treatment are shown. Asterisks indicate significant differences between mutant and wild type. *P <0.05, **P <0.01, ***P <0.001, Student's t test.

Mentions: To determine whether the concentration of a nutrient in the MS medium could alter root growth in vtc1-1, wild-type and vtc1-1 mutant plants were grown on increasing strength of MS medium and primary root length was measured. In the absence of any nutrients (i.e. seedlings grown on agar), primary root length was the same in the wild type and vtc1-1. With increasing concentrations of nutrients, root elongation was strongly inhibited in vtc1-1 in a dose-dependent manner, whereas root growth was only slightly affected in the wild type and the other three vtc mutants (Fig. 3A; see Supplementary Fig. S1 at JXB online). This result confirms that one or more nutrients has or have an inhibitory effect on root development in vtc1-1 when present at high concentrations.


A mutation in GDP-mannose pyrophosphorylase causes conditional hypersensitivity to ammonium, resulting in Arabidopsis root growth inhibition, altered ammonium metabolism, and hormone homeostasis.

Barth C, Gouzd ZA, Steele HP, Imperio RM - J. Exp. Bot. (2009)

Effect of various MS media compositions on primary root development in 7-d-old wild type and vtc1-1. (A) Primary root length when plants were grown on increasing strength of MS medium. Results illustrate means ±SE of 9–23 individual seedlings per genotype and treatment. (B) Primary root length of plants grown in the absence of phosphorous (–P), ammonium nitrate (–NH4+, with potassium nitrate still present) and in the absence of all nitrogen (–N, i.e. no potassium nitrate and no ammonium nitrate). Data represent means ±SE of 6–18 replicates. (C) Effect of increasing concentrations of ammonium chloride (NH4Cl) on root growth in plants grown on 1× MS medium lacking ammonium nitrate (–NH4+), but potassium nitrate still present. Mean values ±SE of 44–102 individual seedlings per genotype and treatment are shown. Asterisks indicate significant differences between mutant and wild type. *P <0.05, **P <0.01, ***P <0.001, Student's t test.
© Copyright Policy - open-access
Related In: Results  -  Collection

License 1 - License 2
Show All Figures
getmorefigures.php?uid=PMC2803207&req=5

fig3: Effect of various MS media compositions on primary root development in 7-d-old wild type and vtc1-1. (A) Primary root length when plants were grown on increasing strength of MS medium. Results illustrate means ±SE of 9–23 individual seedlings per genotype and treatment. (B) Primary root length of plants grown in the absence of phosphorous (–P), ammonium nitrate (–NH4+, with potassium nitrate still present) and in the absence of all nitrogen (–N, i.e. no potassium nitrate and no ammonium nitrate). Data represent means ±SE of 6–18 replicates. (C) Effect of increasing concentrations of ammonium chloride (NH4Cl) on root growth in plants grown on 1× MS medium lacking ammonium nitrate (–NH4+), but potassium nitrate still present. Mean values ±SE of 44–102 individual seedlings per genotype and treatment are shown. Asterisks indicate significant differences between mutant and wild type. *P <0.05, **P <0.01, ***P <0.001, Student's t test.
Mentions: To determine whether the concentration of a nutrient in the MS medium could alter root growth in vtc1-1, wild-type and vtc1-1 mutant plants were grown on increasing strength of MS medium and primary root length was measured. In the absence of any nutrients (i.e. seedlings grown on agar), primary root length was the same in the wild type and vtc1-1. With increasing concentrations of nutrients, root elongation was strongly inhibited in vtc1-1 in a dose-dependent manner, whereas root growth was only slightly affected in the wild type and the other three vtc mutants (Fig. 3A; see Supplementary Fig. S1 at JXB online). This result confirms that one or more nutrients has or have an inhibitory effect on root development in vtc1-1 when present at high concentrations.

Bottom Line: Since VTC1 encodes a GDP-mannose pyrophosphorylase, an enzyme generating GDP-mannose for AA biosynthesis and protein N-glycosylation, it was also tested whether protein N-glycosylation is affected in vtc1-1.Furthermore, since root development requires the action of a variety of hormones, it was investigated whether hormone homeostasis is linked to NH(4)(+) sensitivity in vtc1-1.Our data suggest that NH(4)(+) hypersensitivity in vtc1-1 is caused by disturbed N-glycosylation and that it is associated with auxin and ethylene homeostasis and/or nitric oxide signalling.

View Article: PubMed Central - PubMed

Affiliation: Department of Biology, West Virginia University, 53 Campus Drive, Morgantown, WV 26506-6507, USA. carina.barth@mail.wvu.edu

ABSTRACT
Ascorbic acid (AA) is an antioxidant fulfilling a multitude of cellular functions. Given its pivotal role in maintaining the rate of cell growth and division in the quiescent centre of the root, it was hypothesized that the AA-deficient Arabidopsis thaliana mutants vtc1-1, vtc2-1, vtc3-1, and vtc4-1 have altered root growth. To test this hypothesis, root development was studied in the wild type and vtc mutants grown on Murashige and Skoog medium. It was discovered, however, that only the vtc1-1 mutant has strongly retarded root growth, while the other vtc mutants exhibit a wild-type root phenotype. It is demonstrated that the short-root phenotype in vtc1-1 is independent of AA deficiency and oxidative stress. Instead, vtc1-1 is conditionally hypersensitive to ammonium (NH(4)(+)). To provide new insights into the mechanism of NH(4)(+) sensitivity in vtc1-1, root development, NH(4)(+) content, glutamine synthetase (GS) activity, glutamate dehydrogenase activity, and glutamine content were assessed in wild-type and vtc1-1 mutant plants grown in the presence and absence of high NH(4)(+) and the GS inhibitor MSO. Since VTC1 encodes a GDP-mannose pyrophosphorylase, an enzyme generating GDP-mannose for AA biosynthesis and protein N-glycosylation, it was also tested whether protein N-glycosylation is affected in vtc1-1. Furthermore, since root development requires the action of a variety of hormones, it was investigated whether hormone homeostasis is linked to NH(4)(+) sensitivity in vtc1-1. Our data suggest that NH(4)(+) hypersensitivity in vtc1-1 is caused by disturbed N-glycosylation and that it is associated with auxin and ethylene homeostasis and/or nitric oxide signalling.

Show MeSH
Related in: MedlinePlus