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Sulphur flux through the sulphate assimilation pathway is differently controlled by adenosine 5'-phosphosulphate reductase under stress and in transgenic poplar plants overexpressing gamma-ECS, SO, or APR.

Scheerer U, Haensch R, Mendel RR, Kopriva S, Rennenberg H, Herschbach C - J. Exp. Bot. (2009)

Bottom Line: Sulphate assimilation provides reduced sulphur for the synthesis of cysteine, methionine, and numerous other essential metabolites and secondary compounds.The key step in the pathway is the reduction of activated sulphate, adenosine 5'-phosphosulphate (APS), to sulphite catalysed by APS reductase (APR).Thereby the sulphur flux into GSH or protein remained unaffected. (iii) Cd treatment increased APR activity without any changes in sulphur flux but lowered sulphate uptake.

View Article: PubMed Central - PubMed

Affiliation: Albert-Ludwigs-University Freiburg, Institute of Forest Botany and Tree Physiology, Chair of Tree Physiology, Georges-Köhler-Allee 053/054, Freiburg, Germany.

ABSTRACT
Sulphate assimilation provides reduced sulphur for the synthesis of cysteine, methionine, and numerous other essential metabolites and secondary compounds. The key step in the pathway is the reduction of activated sulphate, adenosine 5'-phosphosulphate (APS), to sulphite catalysed by APS reductase (APR). In the present study, [(35)S]sulphur flux from external sulphate into glutathione (GSH) and proteins was analysed to check whether APR controls the flux through the sulphate assimilation pathway in poplar roots under some stress conditions and in transgenic poplars. (i) O-Acetylserine (OAS) induced APR activity and the sulphur flux into GSH. (ii) The herbicide Acetochlor induced APR activity and results in a decline of GSH. Thereby the sulphur flux into GSH or protein remained unaffected. (iii) Cd treatment increased APR activity without any changes in sulphur flux but lowered sulphate uptake. Several transgenic poplar plants that were manipulated in sulphur metabolism were also analysed. (i) Transgenic poplar plants that overexpressed the gamma-glutamylcysteine synthetase (gamma-ECS) gene, the enzyme catalysing the key step in GSH formation, showed an increase in sulphur flux into GSH and sulphate uptake when gamma-ECS was targeted to the cytosol, while no changes in sulphur flux were observed when gamma-ECS was targeted to plastids. (ii) No effect on sulphur flux was observed when the sulphite oxidase (SO) gene from Arabidopsis thaliana, which catalyses the back reaction of APR, that is the reaction from sulphite to sulphate, was overexpressed. (iii) When Lemna minor APR was overexpressed in poplar, APR activity increased as expected, but no changes in sulphur flux were observed. For all of these experiments the flux control coefficient for APR was calculated. APR as a controlling step in sulphate assimilation seems obvious under OAS treatment, in gamma-ECS and SO overexpressing poplars. A possible loss of control under certain conditions, that is Cd treatment, Acetochlor treatment, and in APR overexpressing poplar, is discussed.

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Sulphur metabolite contents and 35S flux into different metabolite pools of fine roots excised from poplar plants pre-treated with Cd. Fine roots were excised from poplar trees watered without (A, n=10) or with 0.5 mM Cd (B, n=10) in the nutrient solution for 4 weeks. The excised fine roots were pre-incubated for 2 h and subsequently exposed to [35S]sulphate for 4 h to measure sulphate uptake and 35S flux into different metabolite pools. Sulphate (μmol g−1 FW), GSH (nmol g−1 FW), and protein (mg g−1 FW) contents were determined (pink squares). 35S flux into internal sulphate, GSH, and protein is given as pmol 35S g−1 FW h−1 (light blue squares). APR activity is indicated in a green square as nmol mg−1 protein min−1. Significant differences at P <0.05 from control roots without Cd pre-treatment are indicated by asterisks.
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fig2: Sulphur metabolite contents and 35S flux into different metabolite pools of fine roots excised from poplar plants pre-treated with Cd. Fine roots were excised from poplar trees watered without (A, n=10) or with 0.5 mM Cd (B, n=10) in the nutrient solution for 4 weeks. The excised fine roots were pre-incubated for 2 h and subsequently exposed to [35S]sulphate for 4 h to measure sulphate uptake and 35S flux into different metabolite pools. Sulphate (μmol g−1 FW), GSH (nmol g−1 FW), and protein (mg g−1 FW) contents were determined (pink squares). 35S flux into internal sulphate, GSH, and protein is given as pmol 35S g−1 FW h−1 (light blue squares). APR activity is indicated in a green square as nmol mg−1 protein min−1. Significant differences at P <0.05 from control roots without Cd pre-treatment are indicated by asterisks.

Mentions: Poplar trees were pre-treated with 0.5 mM CdCl2 added to the Hoagland nutrient solution during watering for 4 weeks. This treatment resulted in an 18-fold increase in APR activity of the fine roots. Protein and GSH contents were not affected, while the sulphate content was reduced by ∼50% (Fig. 2). Accordingly, sulphate uptake in Cd-treated plants was significantly reduced by 22% (Table 1). However, 35S flux into GSH or proteins was not affected, while the flux into the internal sulphate pool was reduced (Fig. 2). In addition, the ratio between soluble and insoluble 35S was diminished due to the Cd treatment (Table 1).


Sulphur flux through the sulphate assimilation pathway is differently controlled by adenosine 5'-phosphosulphate reductase under stress and in transgenic poplar plants overexpressing gamma-ECS, SO, or APR.

Scheerer U, Haensch R, Mendel RR, Kopriva S, Rennenberg H, Herschbach C - J. Exp. Bot. (2009)

Sulphur metabolite contents and 35S flux into different metabolite pools of fine roots excised from poplar plants pre-treated with Cd. Fine roots were excised from poplar trees watered without (A, n=10) or with 0.5 mM Cd (B, n=10) in the nutrient solution for 4 weeks. The excised fine roots were pre-incubated for 2 h and subsequently exposed to [35S]sulphate for 4 h to measure sulphate uptake and 35S flux into different metabolite pools. Sulphate (μmol g−1 FW), GSH (nmol g−1 FW), and protein (mg g−1 FW) contents were determined (pink squares). 35S flux into internal sulphate, GSH, and protein is given as pmol 35S g−1 FW h−1 (light blue squares). APR activity is indicated in a green square as nmol mg−1 protein min−1. Significant differences at P <0.05 from control roots without Cd pre-treatment are indicated by asterisks.
© Copyright Policy - open-access
Related In: Results  -  Collection

License 1 - License 2
Show All Figures
getmorefigures.php?uid=PMC2803220&req=5

fig2: Sulphur metabolite contents and 35S flux into different metabolite pools of fine roots excised from poplar plants pre-treated with Cd. Fine roots were excised from poplar trees watered without (A, n=10) or with 0.5 mM Cd (B, n=10) in the nutrient solution for 4 weeks. The excised fine roots were pre-incubated for 2 h and subsequently exposed to [35S]sulphate for 4 h to measure sulphate uptake and 35S flux into different metabolite pools. Sulphate (μmol g−1 FW), GSH (nmol g−1 FW), and protein (mg g−1 FW) contents were determined (pink squares). 35S flux into internal sulphate, GSH, and protein is given as pmol 35S g−1 FW h−1 (light blue squares). APR activity is indicated in a green square as nmol mg−1 protein min−1. Significant differences at P <0.05 from control roots without Cd pre-treatment are indicated by asterisks.
Mentions: Poplar trees were pre-treated with 0.5 mM CdCl2 added to the Hoagland nutrient solution during watering for 4 weeks. This treatment resulted in an 18-fold increase in APR activity of the fine roots. Protein and GSH contents were not affected, while the sulphate content was reduced by ∼50% (Fig. 2). Accordingly, sulphate uptake in Cd-treated plants was significantly reduced by 22% (Table 1). However, 35S flux into GSH or proteins was not affected, while the flux into the internal sulphate pool was reduced (Fig. 2). In addition, the ratio between soluble and insoluble 35S was diminished due to the Cd treatment (Table 1).

Bottom Line: Sulphate assimilation provides reduced sulphur for the synthesis of cysteine, methionine, and numerous other essential metabolites and secondary compounds.The key step in the pathway is the reduction of activated sulphate, adenosine 5'-phosphosulphate (APS), to sulphite catalysed by APS reductase (APR).Thereby the sulphur flux into GSH or protein remained unaffected. (iii) Cd treatment increased APR activity without any changes in sulphur flux but lowered sulphate uptake.

View Article: PubMed Central - PubMed

Affiliation: Albert-Ludwigs-University Freiburg, Institute of Forest Botany and Tree Physiology, Chair of Tree Physiology, Georges-Köhler-Allee 053/054, Freiburg, Germany.

ABSTRACT
Sulphate assimilation provides reduced sulphur for the synthesis of cysteine, methionine, and numerous other essential metabolites and secondary compounds. The key step in the pathway is the reduction of activated sulphate, adenosine 5'-phosphosulphate (APS), to sulphite catalysed by APS reductase (APR). In the present study, [(35)S]sulphur flux from external sulphate into glutathione (GSH) and proteins was analysed to check whether APR controls the flux through the sulphate assimilation pathway in poplar roots under some stress conditions and in transgenic poplars. (i) O-Acetylserine (OAS) induced APR activity and the sulphur flux into GSH. (ii) The herbicide Acetochlor induced APR activity and results in a decline of GSH. Thereby the sulphur flux into GSH or protein remained unaffected. (iii) Cd treatment increased APR activity without any changes in sulphur flux but lowered sulphate uptake. Several transgenic poplar plants that were manipulated in sulphur metabolism were also analysed. (i) Transgenic poplar plants that overexpressed the gamma-glutamylcysteine synthetase (gamma-ECS) gene, the enzyme catalysing the key step in GSH formation, showed an increase in sulphur flux into GSH and sulphate uptake when gamma-ECS was targeted to the cytosol, while no changes in sulphur flux were observed when gamma-ECS was targeted to plastids. (ii) No effect on sulphur flux was observed when the sulphite oxidase (SO) gene from Arabidopsis thaliana, which catalyses the back reaction of APR, that is the reaction from sulphite to sulphate, was overexpressed. (iii) When Lemna minor APR was overexpressed in poplar, APR activity increased as expected, but no changes in sulphur flux were observed. For all of these experiments the flux control coefficient for APR was calculated. APR as a controlling step in sulphate assimilation seems obvious under OAS treatment, in gamma-ECS and SO overexpressing poplars. A possible loss of control under certain conditions, that is Cd treatment, Acetochlor treatment, and in APR overexpressing poplar, is discussed.

Show MeSH
Related in: MedlinePlus