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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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Exogenous glucose retards seed germination. Seeds were sown on Arabidopsis minimal media supplemented with the indicated additives. Seed germination, defined as the emergence of any part of the seedling from the seed coat, was scored at regular intervals. Results presented are means ± SD (n = 4). Glc, glucose; Sorb, sorbitol. This experiment was repeated, with similar results.
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Figure 4: Exogenous glucose retards seed germination. Seeds were sown on Arabidopsis minimal media supplemented with the indicated additives. Seed germination, defined as the emergence of any part of the seedling from the seed coat, was scored at regular intervals. Results presented are means ± SD (n = 4). Glc, glucose; Sorb, sorbitol. This experiment was repeated, with similar results.

Mentions: The effects of high glucose concentrations on lipid breakdown could be due to a non-specific inhibition of developmental and/or metabolic processes. Consistent with this possibility are findings that seedlings arrested by growth on very high concentrations of sorbitol (0.4 M sorbitol + 0.03 M Glc) also retain almost all of their 20:1 (Figure 3). However, although the effects of 0.4 M sorbitol + 0.03 M Glc on lipid mobilization are comparable to the effects of 0.3 M Glc, 0.4 M sorbitol + 0.03 M Glc inhibits lipid accumulation to a significantly greater extent than 0.3 M Glc (Table 1). For example, seedlings grown for 22 days in the presence of 0.3 M Glc accumulate approximately twice as much membrane fatty acid as seedlings grown on 0.4 M sorbitol + 0.03 M Glc. These results suggest that the inhibitory effects of 0.4 M sorbitol + 0.03 M Glc on lipid breakdown are less specific than the effects of 0.3 M Glc. Both 0.3 M Glc and 0.4 M sorbitol + 0.03 M Glc also retard seed germination rates (Figure 4). However, both these media supplements delay seed germination by only 4 to 5 days. In contrast, storage lipid mobilization is retarded for a significantly longer time period. For example, whereas seedlings growing in the absence of added Glc or sorbitol mobilize approximately 50% of their 20:1 within 3 days of the start of imbibition (Figure 1), seedlings grown on 0.3 M Glc or 0.4 M sorb + 0.03 M Glc mobilize only 20 to 30% of their 20:1 after 22 days (Figure 3).


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)

Exogenous glucose retards seed germination. Seeds were sown on Arabidopsis minimal media supplemented with the indicated additives. Seed germination, defined as the emergence of any part of the seedling from the seed coat, was scored at regular intervals. Results presented are means ± SD (n = 4). Glc, glucose; Sorb, sorbitol. This experiment was repeated, with similar results.
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Related In: Results  -  Collection

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getmorefigures.php?uid=PMC113751&req=5

Figure 4: Exogenous glucose retards seed germination. Seeds were sown on Arabidopsis minimal media supplemented with the indicated additives. Seed germination, defined as the emergence of any part of the seedling from the seed coat, was scored at regular intervals. Results presented are means ± SD (n = 4). Glc, glucose; Sorb, sorbitol. This experiment was repeated, with similar results.
Mentions: The effects of high glucose concentrations on lipid breakdown could be due to a non-specific inhibition of developmental and/or metabolic processes. Consistent with this possibility are findings that seedlings arrested by growth on very high concentrations of sorbitol (0.4 M sorbitol + 0.03 M Glc) also retain almost all of their 20:1 (Figure 3). However, although the effects of 0.4 M sorbitol + 0.03 M Glc on lipid mobilization are comparable to the effects of 0.3 M Glc, 0.4 M sorbitol + 0.03 M Glc inhibits lipid accumulation to a significantly greater extent than 0.3 M Glc (Table 1). For example, seedlings grown for 22 days in the presence of 0.3 M Glc accumulate approximately twice as much membrane fatty acid as seedlings grown on 0.4 M sorbitol + 0.03 M Glc. These results suggest that the inhibitory effects of 0.4 M sorbitol + 0.03 M Glc on lipid breakdown are less specific than the effects of 0.3 M Glc. Both 0.3 M Glc and 0.4 M sorbitol + 0.03 M Glc also retard seed germination rates (Figure 4). However, both these media supplements delay seed germination by only 4 to 5 days. In contrast, storage lipid mobilization is retarded for a significantly longer time period. For example, whereas seedlings growing in the absence of added Glc or sorbitol mobilize approximately 50% of their 20:1 within 3 days of the start of imbibition (Figure 1), seedlings grown on 0.3 M Glc or 0.4 M sorb + 0.03 M Glc mobilize only 20 to 30% of their 20:1 after 22 days (Figure 3).

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