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Mobilization of seed storage lipid by Arabidopsis seedlings is retarded in the presence of exogenous sugars.

To JP, Reiter WD, Gibson SI - BMC Plant Biol. (2002)

Bottom Line: Wild-type seedlings become insensitive to glucose inhibition of storage lipid breakdown within 3 days of the start of imbibition.This effect is not solely due to the osmotic potential of the media, as substantially higher concentrations of sorbitol than of glucose are required to exert significant effects on lipid breakdown.The inhibitory effect of glucose on lipid breakdown is limited to a narrow developmental window, suggesting that completion of some critical metabolic transition results in loss of sensitivity to the inhibitory effect of glucose on lipid breakdown.

View Article: PubMed Central - HTML - PubMed

Affiliation: Department of Biochemistry & Cell Biology, MS140 Rice University, 6100 Main St, Houston, TX 77005-1892, USA. jennto@email.unc.edu

ABSTRACT

Background: Soluble sugar levels must be closely regulated in germinating seeds to ensure an adequate supply of energy and building materials for the developing seedling. Studies on germinating cereal seeds indicate that production of sugars from starch is inhibited by increasing sugar levels. Although numerous studies have focused on the regulation of starch metabolism, very few studies have addressed the control of storage lipid metabolism by germinating oilseeds.

Results: Mobilization of storage lipid by germinating seeds of the model oilseed plant Arabidopsis thaliana (L.) Heynh. occurs at a greatly reduced rate in the presence of exogenous glucose or mannose, but not in the presence of equi-molar 3-O-methylglucose or sorbitol. The sugar-insensitive5-1/abscisic acid-insensitive4-101 (sis5-1/abi4-101) mutant is resistant to glucose inhibition of seed storage lipid mobilization. Wild-type seedlings become insensitive to glucose inhibition of storage lipid breakdown within 3 days of the start of imbibition.

Conclusions: Growth in the presence of exogenous glucose significantly retards mobilization of seed storage lipid in germinating seeds from wild-type Arabidopsis. This effect is not solely due to the osmotic potential of the media, as substantially higher concentrations of sorbitol than of glucose are required to exert significant effects on lipid breakdown. The inhibitory effect of glucose on lipid breakdown is limited to a narrow developmental window, suggesting that completion of some critical metabolic transition results in loss of sensitivity to the inhibitory effect of glucose on lipid breakdown.

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Effects of glucose analogs on seed storage lipid breakdown. Eicosenoic (20:1) fatty acid levels were measured in seeds/seedlings harvested from the indicated media at different times after the start of imbibition. Results presented are means ± SD (n = 3). Glc, glucose; Man, mannose; 3-OMG, 3-O-methylglucose; Sorb, sorbitol. This experiment was repeated, with similar results.
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Figure 2: Effects of glucose analogs on seed storage lipid breakdown. Eicosenoic (20:1) fatty acid levels were measured in seeds/seedlings harvested from the indicated media at different times after the start of imbibition. Results presented are means ± SD (n = 3). Glc, glucose; Man, mannose; 3-OMG, 3-O-methylglucose; Sorb, sorbitol. This experiment was repeated, with similar results.

Mentions: Mannose is a glucose analog that has been postulated to affect seed germination [19] and sugar-regulated gene expression [31,32] via a signaling pathway that requires hexokinase activity. For reasons that remain unclear, mannose inhibits seed germination and early seedling development at concentrations that are 100–200 fold lower than the concentrations of glucose required to exert similar effects [19,46-48,50]. As shown in Figure 2, growth on low (1.4 mM) concentrations of mannose also leads to a significant reduction in 20:1 breakdown. In contrast, 3-O-methylglucose has little effect on 20:1 levels (Figure 2). 3-O-methylglucose is a glucose analog that, in at least some organisms, is transported by hexose transporters [61-64] but is phosphorylated very inefficiently, if at all, by hexokinases [62]. Seedlings grown on media containing 3-O-methylglucose have 20:1 levels that are similar to the 20:1 levels of plants grown on approximately equi-molar concentrations of sorbitol, but that are much lower than the 20:1 levels of plants grown on equi-molar concentrations of glucose (Figure 2).


Mobilization of seed storage lipid by Arabidopsis seedlings is retarded in the presence of exogenous sugars.

To JP, Reiter WD, Gibson SI - BMC Plant Biol. (2002)

Effects of glucose analogs on seed storage lipid breakdown. Eicosenoic (20:1) fatty acid levels were measured in seeds/seedlings harvested from the indicated media at different times after the start of imbibition. Results presented are means ± SD (n = 3). Glc, glucose; Man, mannose; 3-OMG, 3-O-methylglucose; Sorb, sorbitol. This experiment was repeated, with similar results.
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC113751&req=5

Figure 2: Effects of glucose analogs on seed storage lipid breakdown. Eicosenoic (20:1) fatty acid levels were measured in seeds/seedlings harvested from the indicated media at different times after the start of imbibition. Results presented are means ± SD (n = 3). Glc, glucose; Man, mannose; 3-OMG, 3-O-methylglucose; Sorb, sorbitol. This experiment was repeated, with similar results.
Mentions: Mannose is a glucose analog that has been postulated to affect seed germination [19] and sugar-regulated gene expression [31,32] via a signaling pathway that requires hexokinase activity. For reasons that remain unclear, mannose inhibits seed germination and early seedling development at concentrations that are 100–200 fold lower than the concentrations of glucose required to exert similar effects [19,46-48,50]. As shown in Figure 2, growth on low (1.4 mM) concentrations of mannose also leads to a significant reduction in 20:1 breakdown. In contrast, 3-O-methylglucose has little effect on 20:1 levels (Figure 2). 3-O-methylglucose is a glucose analog that, in at least some organisms, is transported by hexose transporters [61-64] but is phosphorylated very inefficiently, if at all, by hexokinases [62]. Seedlings grown on media containing 3-O-methylglucose have 20:1 levels that are similar to the 20:1 levels of plants grown on approximately equi-molar concentrations of sorbitol, but that are much lower than the 20:1 levels of plants grown on equi-molar concentrations of glucose (Figure 2).

Bottom Line: Wild-type seedlings become insensitive to glucose inhibition of storage lipid breakdown within 3 days of the start of imbibition.This effect is not solely due to the osmotic potential of the media, as substantially higher concentrations of sorbitol than of glucose are required to exert significant effects on lipid breakdown.The inhibitory effect of glucose on lipid breakdown is limited to a narrow developmental window, suggesting that completion of some critical metabolic transition results in loss of sensitivity to the inhibitory effect of glucose on lipid breakdown.

View Article: PubMed Central - HTML - PubMed

Affiliation: Department of Biochemistry & Cell Biology, MS140 Rice University, 6100 Main St, Houston, TX 77005-1892, USA. jennto@email.unc.edu

ABSTRACT

Background: Soluble sugar levels must be closely regulated in germinating seeds to ensure an adequate supply of energy and building materials for the developing seedling. Studies on germinating cereal seeds indicate that production of sugars from starch is inhibited by increasing sugar levels. Although numerous studies have focused on the regulation of starch metabolism, very few studies have addressed the control of storage lipid metabolism by germinating oilseeds.

Results: Mobilization of storage lipid by germinating seeds of the model oilseed plant Arabidopsis thaliana (L.) Heynh. occurs at a greatly reduced rate in the presence of exogenous glucose or mannose, but not in the presence of equi-molar 3-O-methylglucose or sorbitol. The sugar-insensitive5-1/abscisic acid-insensitive4-101 (sis5-1/abi4-101) mutant is resistant to glucose inhibition of seed storage lipid mobilization. Wild-type seedlings become insensitive to glucose inhibition of storage lipid breakdown within 3 days of the start of imbibition.

Conclusions: Growth in the presence of exogenous glucose significantly retards mobilization of seed storage lipid in germinating seeds from wild-type Arabidopsis. This effect is not solely due to the osmotic potential of the media, as substantially higher concentrations of sorbitol than of glucose are required to exert significant effects on lipid breakdown. The inhibitory effect of glucose on lipid breakdown is limited to a narrow developmental window, suggesting that completion of some critical metabolic transition results in loss of sensitivity to the inhibitory effect of glucose on lipid breakdown.

Show MeSH
Related in: MedlinePlus