Comparative Enzymic Studies of Sucrose Metabolism in the Taproots and Fibrous Roots of <i>Beta vulgaris</i> L

Silvius, John E.; Snyder, F. W.

doi:10.1104/pp.64.6.1070

Cited by 28 publications

(25 citation statements)

References 11 publications

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“…However, less than 0.1 nmol of ADP/g dry weight was detected in the taproot. This is consistent with the reported presence of an ADP-dependent sucrose synthase in fibrous roots and absence of it in taproot extracts (5). The presence of significantly higher levels of ADP in the fibrous roots than in taproots, combined with previously reported enzyme kinetic data suggesting that fibrous root sucrose synthase has a greater affmity for ADP as substrate (5), strongly indicates a possible regulatory role for ADP-dependent sucrose synthase in the fibrous roots of sugarbeet.…”

Section: Resultssupporting

confidence: 80%

“…In addition, the fibrous root sucrose synthase was inhibited by UDP at concentrations above 10 mm. The UDP-dependent sucrose synthase is believed to play a key role in the development of sucrose storage capacity of sugarbeet taproots (1,2,5). Taproots used in the present study were already actively accumulating sucrose (4).…”

Section: Resultsmentioning

confidence: 94%

“…These data are consistent with our previous report of UDPdependent sucrose synthase activity in both the taproot and fibrous roots of sugarbeet (5). However, the taproot enzyme has a higher Vma.x and higher affinity for UDP than the fibrous root enzyme (5). In addition, the fibrous root sucrose synthase was inhibited by UDP at concentrations above 10 mm.…”

Section: Resultsmentioning

confidence: 96%

“…Sucrose synthase (EC 2.4.1.13) activity was observed in both taproot and fibrous roots, but the taproot sucrose synthase showed a higher affinity for UDP than for ADP as substrate, as inferred from the respective Km values. Conversely, the fibrous root enzyme had a higher affinity for ADP (5 two root types represent competing sinks for sucrose. Therefore, the rate of enzymic cleavage of sucrose in one sink versus the other may influence allocation between the two sinks.…”

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confidence: 99%

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Nucleoside Diphosphate Levels in Taproots and Fibrous Roots of Beta vulgaris L.

Silvius¹,

Snyder²,

Kremer³

1982

Plant Physiol.

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Sucrose synthase (EC 2.4.1.13) of sugarbeet (Beta vulgaris L.) fibrous roots has a distinctly different order of preference for nucleoside diphosphate substrates than that of the taproot enzyme Plant Physiol 64: 1070-1073. Separation and quantitation of UDP, ADP, and GDP in root extracts by high-pressure liquid chromatography revealed that UDP levels in taproot tissue were 5 to 10 times greater than those of fibrous root tissues. The lower fibrous root UDP levels were associated with significantly higher ADP and GDP levels in these roots as compared to the taproot. These differences are consistent with differences in the substrate affinity of sucrose synthase and suggest a regulatory role of the enzyme in the control of sucrose cleavage and utilization between the two root types.Photosynthate partitioning among plant growth centers may be controlled by their relative mobilizing capacities (7). Mobilization of sucrose by sugarbeet (Beta vulgaris L.) storage roots (taproots) involves both enzymic conversions and membrane transport processes resulting in allocation of the photosynthate between root growth and sucrose storage (1, 3).Our previous studies have demonstrated that photosynthate partitioning between sugarbeet taproots and fibrous roots (expressed quantitatively as TFWR2) is genetically controlled (6). The TFWR, in turn, is positively correlated with photosynthate partitioning between taproot and leaf laminae (expressed as TLWR) (4), and both partitioning parameters are correlated with the activity of enzymes of sucrose metabolism in the taproot (4). Sucrose synthase (EC 2.4.1.13) activity was observed in both taproot and fibrous roots, but the taproot sucrose synthase showed a higher affinity for UDP than for ADP as substrate, as inferred from the respective Km values. Conversely, the fibrous root enzyme had a higher affinity for ADP (5). Other NDP substrates were ranked in distinctly different orders of affmity for the taproot compared to the fibrous root sucrose synthase. two root types represent competing sinks for sucrose. Therefore, the rate of enzymic cleavage of sucrose in one sink versus the other may influence allocation between the two sinks. Furthermore, different NDP substrate affmities for taproot versus fibrous root sucrose synthase suggests a mechanism to control independently the enzyme activity in each of the two adjacent sinks.In order to validate a regulatory role for the UDP-and ADPdependent sucrose synthases, it was necessary to determine the relative levels of these and related NDPs in the tissues of taproots and fibrous roots. The results of these experiments are reported herein. MATERIALS AND METHODSPlant Material. Sugarbeet plants of breeding line EL-40 were grown from seed in a controlled environment chamber as described previously (4), and plants were harvested at 35 d postemergence. Taproots and fibrous roots were separated, frozen in liquid N2, and lyophilized. Inasmuch as individual root mass per plant was too small for the analyses, taproots and fibrous roots of ea...

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Section: Resultssupporting

confidence: 80%

Section: Resultsmentioning

confidence: 94%

Section: Resultsmentioning

confidence: 96%

mentioning

confidence: 99%

See 2 more Smart Citations

Nucleoside Diphosphate Levels in Taproots and Fibrous Roots of Beta vulgaris L.

Silvius¹,

Snyder²,

Kremer³

1982

Plant Physiol.

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“…In sugar-storing plant tissues, shifts in carbohydrate composition are usually accompanied by shifts in the relative activities of these sucrose metabolizing enzymes. However, most ofthese studies were confined to vegetative tissues such as sugarcane stems (Saccharum spp; [3]), sugarbeet roots (Beta vulgaris L.; [17]), and bean leaves (Phaseolus vulgaris L.; [13] (Fig. 1).…”

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confidence: 99%

Sucrose Metabolism in Netted Muskmelon Fruit during Development

Lingle

Dunlap²

1987

Plant Physiol.

130

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ABSTRACrSupr content and composition are major criteria used in judging the quality of netted muskmelon (Cwucmis melo L. var reticulatus) fruit. Sugar composition and four enzymes of sucrose metabolism were determined in 'MNum 45' muskmelon fruit at 10-day intervals binig 10 days after pollination (DAP) until full-slip (35 DAP). Sugar content increased in both outer (green) mesocarp and inner (orange) mesocarp between 20 and 30 DAP. The major proportion of total increase in sugar was attributed to sucrose accumulation. The large increase in sucrose relative to glucose and fructose was accompanied by a dramatic decrease in acid invertase activity, which was highest in both tissues at 10 and 20 DAP, and increases in sucrose phosphate synthase (SPS) and sucrose synthase activities. The green tissue had a lower propordto of total sugar as sucrose, greater invertase activity, and less SPS activity than the orange tissue. Changes in relative sucrose content were highly correlated with changes in enzyme activity. The results strongly suggest that increases in the proportion of sucrose found in melon fruit were associated with a decline in acid invertase activity and an increase in SPS activity approximately 10 days before full-slip. Therefore, these enzymes apparently play a key role in determining sugar composition and the quality of muskmelon fruit. Ethylene. Tissue cylinders were taken along the equatorial plane of each fruit with a 0.8 cm diameter cork borer and cut to a uniform length of 2.5 cm. The tissue cylinders were divided into a 0.5 cm portion including the rind and the remaining 2.0 cm segment made up of the inner orange tissue. Each segment was placed in a 12 x 75 mm glass vial and capped with a rubber serum cap. The headspace gas was allowed to accumulate for 0.5 to 2 h; 1 ml was then analyzed for ethylene by FID-gas chromatography on an alumina column (2.46 m x 0.32 cm).Sugar extraction and analysis. Four cylinders of tissue were taken from each melon as desibed above using a 1.9 cm diameter cork borer. The netting was removed, and the cylinders of mesocarp were divided into the outer 0.5 cm (green) and the inner 2.0 cm (orange). Tissue was weighed and frozen at -80°C

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