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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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High concentrations of glucose nearly eliminate breakdown of seed storage lipids. Seedlings were grown on the indicated media for 14 or 22 days prior to collection for fatty acid analysis. The majority of seedlings grown on 0.27 M glucose, 0.3 M glucose or 0.4 M sorbitol + 0.03 M glucose exhibit arrested development. However, some of the seedlings grown on these media escape the selection, as shown by development of relatively normal shoot systems, and were not collected for analysis. Seedlings grown on 0.03 M glucose, 0.24 M sorbitol + 0.03 M glucose or 0.27 M sorbitol + 0.03 M glucose exhibit a nearly uniform morphology, and so all seedlings from these media were collected for analysis. 20:1 fatty acid levels are expressed relative to the amount of 20:1 fatty acid present in seeds prior to the start of imbibition. Note that the amount of 20:1 fatty acid present in ungerminated seeds was obtained from independent experiments. Results presented are means ± SD (n = 3). Glc, glucose; Sorb, sorbitol. This experiment was repeated, with similar results.
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Figure 3: High concentrations of glucose nearly eliminate breakdown of seed storage lipids. Seedlings were grown on the indicated media for 14 or 22 days prior to collection for fatty acid analysis. The majority of seedlings grown on 0.27 M glucose, 0.3 M glucose or 0.4 M sorbitol + 0.03 M glucose exhibit arrested development. However, some of the seedlings grown on these media escape the selection, as shown by development of relatively normal shoot systems, and were not collected for analysis. Seedlings grown on 0.03 M glucose, 0.24 M sorbitol + 0.03 M glucose or 0.27 M sorbitol + 0.03 M glucose exhibit a nearly uniform morphology, and so all seedlings from these media were collected for analysis. 20:1 fatty acid levels are expressed relative to the amount of 20:1 fatty acid present in seeds prior to the start of imbibition. Note that the amount of 20:1 fatty acid present in ungerminated seeds was obtained from independent experiments. Results presented are means ± SD (n = 3). Glc, glucose; Sorb, sorbitol. This experiment was repeated, with similar results.

Mentions: Growth on high (0.27 to 0.33 M) concentrations of glucose or sucrose has been shown to severely inhibit development of Arabidopsis seedlings [33,46-50,55]. Most seedlings grown on high-sugar media lack true leaves and have cotyledons that have undergone little expansion, even after two to three weeks of growth. As more moderate sugar concentrations slow 20:1 mobilization (Figure 1), it was of interest to determine whether seedlings arrested by growth on high-sugar media are able to mobilize any of their seed storage lipid. As shown in Figure 3, seedlings arrested by growth on 0.3 M glucose retain approximately 80% of their seed storage lipid, even after 22 days of growth. In contrast, 22-day old seedlings grown in the presence of equi-molar sorbitol retain only 4 to 5% of their seed storage lipid.


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)

High concentrations of glucose nearly eliminate breakdown of seed storage lipids. Seedlings were grown on the indicated media for 14 or 22 days prior to collection for fatty acid analysis. The majority of seedlings grown on 0.27 M glucose, 0.3 M glucose or 0.4 M sorbitol + 0.03 M glucose exhibit arrested development. However, some of the seedlings grown on these media escape the selection, as shown by development of relatively normal shoot systems, and were not collected for analysis. Seedlings grown on 0.03 M glucose, 0.24 M sorbitol + 0.03 M glucose or 0.27 M sorbitol + 0.03 M glucose exhibit a nearly uniform morphology, and so all seedlings from these media were collected for analysis. 20:1 fatty acid levels are expressed relative to the amount of 20:1 fatty acid present in seeds prior to the start of imbibition. Note that the amount of 20:1 fatty acid present in ungerminated seeds was obtained from independent experiments. Results presented are means ± SD (n = 3). Glc, glucose; Sorb, sorbitol. This experiment was repeated, with similar results.
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Figure 3: High concentrations of glucose nearly eliminate breakdown of seed storage lipids. Seedlings were grown on the indicated media for 14 or 22 days prior to collection for fatty acid analysis. The majority of seedlings grown on 0.27 M glucose, 0.3 M glucose or 0.4 M sorbitol + 0.03 M glucose exhibit arrested development. However, some of the seedlings grown on these media escape the selection, as shown by development of relatively normal shoot systems, and were not collected for analysis. Seedlings grown on 0.03 M glucose, 0.24 M sorbitol + 0.03 M glucose or 0.27 M sorbitol + 0.03 M glucose exhibit a nearly uniform morphology, and so all seedlings from these media were collected for analysis. 20:1 fatty acid levels are expressed relative to the amount of 20:1 fatty acid present in seeds prior to the start of imbibition. Note that the amount of 20:1 fatty acid present in ungerminated seeds was obtained from independent experiments. Results presented are means ± SD (n = 3). Glc, glucose; Sorb, sorbitol. This experiment was repeated, with similar results.
Mentions: Growth on high (0.27 to 0.33 M) concentrations of glucose or sucrose has been shown to severely inhibit development of Arabidopsis seedlings [33,46-50,55]. Most seedlings grown on high-sugar media lack true leaves and have cotyledons that have undergone little expansion, even after two to three weeks of growth. As more moderate sugar concentrations slow 20:1 mobilization (Figure 1), it was of interest to determine whether seedlings arrested by growth on high-sugar media are able to mobilize any of their seed storage lipid. As shown in Figure 3, seedlings arrested by growth on 0.3 M glucose retain approximately 80% of their seed storage lipid, even after 22 days of growth. In contrast, 22-day old seedlings grown in the presence of equi-molar sorbitol retain only 4 to 5% of their seed storage lipid.

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