Accumulation and conversion of sugars by developing wheat grains. 3. Non‐diffusional uptake of sucrose, the substrate preferred by endosperm slices

Rijven, A. H. G. C.; Gifford, Roger M.

doi:10.1111/j.1365-3040.1983.tb01275.x

Cited by 28 publications

(26 citation statements)

References 14 publications

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“…Starch was estimated essentially as described before (14), incubating each replicate with 0.25 mg porcine pancreatic a-amylase and with 1 mg Rhizopus niveus glucoamylase (7) (instead of ,@-amylase) for 0.5 h at 40°C and 2.5 h at 50°C in an acetate buffer at pH 4.8. The 70% ethanol-soluble fraction formed was deemed to represent starch.…”

Section: Methodsmentioning

confidence: 99%

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Heat Inactivation of Starch Synthase in Wheat Endosperm Tissue

Rijven¹

1986

Plant Physiol.

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ABSTRACIThe effect of temperature on accumulation of starch was studied in grain slices of wheat (Titicum aestivum cv SUN9E), taken 15 days after anthesis. As compared with pretreatment of such slices at 25°C, pretreatment at 30 or 35C reduced the subsequent conversion of sucrose to starch. In contrast to rice (Oryza sativa cv Calrose), pretreatment of wheat soluble starch synthase in vitro at 30°C or higher temperatures reduced its activity. In zymograms using nondenaturing polyacrylamide gel electrophoresis followed by activity staining, the slowest mirating band represented the most temperature sensitive isozyme. Although preincubation of a soluble enzyme sample in vitro at 25°C did not result in loss of starch synthase activity, it did result in a gradual shift of zymogram banding pattern toward faster migrating species. Pretreatment of isolated starch granules at 40°C increased their bound starch synthase activity. Both soluble and bound enzymes in the grains of whole wheat plants lost activity when the plants were held above 30°C for 30 minutes or longer. Both activities lost from the grains after a 1 hour treatment at 37°C were restored in 1 to 2 days by a return to 21°C. In slices, inactivation of the soluble starch synthase was increased by incubation with 2,4-dinitrophenol. It is tentatively suggested that in vivo heat inactivation of soluble starch synthase may be a direct effect of heat on the enzyme protein and that of bound enzyme an indirect effect involving metabolic factors.In wheat the optimum temperature, of plant culture for dry weight per grain at maturity occurs at a day/night temperature of 15°C/10°C (4). Increasing the temperature of the ear independent of the rest of the plant from 15 to 20°C and 25C has resulted in an increased growth rate of the ear but this was accompanied by earlier senescence and a shorter duration of growth (6). Ear warming at 33°C/25°C (day/night) in comparison with 2 1C/16°C, resulted in a reduction ofgrain growth rate after the 6 d warming period (1). From these data, it would be expected that at a suitably high temperature such a reduction in rate could be observed earlier and analyzed more directly. Also it has been suggested that for maize kernels grown in vitro, the adverse effects of high temperature on starch synthesis during the grain-fill period were due to deficiencies in the synthetic process rather than in the supply of substrate (8)

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Section: Methodsmentioning

confidence: 99%

“…As a control, label in starch granules, incorporated in a starch synthase reaction as described below, was 96 to 100% solubilized by the above incubation. Label in the insoluble residue was solubilized by acid hydrolysis (14).…”

Section: Methodsmentioning

confidence: 99%

Heat Inactivation of Starch Synthase in Wheat Endosperm Tissue

Rijven¹

1986

Plant Physiol.

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“…up to near saturation at 150 to 200 mm (13,19,26). Such data have been taken to indicate that grain filling is substrate limited in vivo, given the sucrose concentration in the endosperm cavity (10,12,16).…”

Section: Solute Concentrations and Grain Filling Rate In Wheatmentioning

confidence: 99%

“…Hence, if sucrose uptake and conversion in vivo is related to such osmotic control, the in vitro kinetics may be quantitatively wrong. One concern with the cultured endosperm is that, although in long term uptake studies (about 3 d) sucrose uptake could exceed in vivo growth rates, the rate of its conversion to starch was only half the rate of uptake (13,26). Another relates to the 02 sensitivity of in vitro grain growth (14).…”

Section: Solute Concentrations and Grain Filling Rate In Wheatmentioning

confidence: 99%

“…In cultured ears, the grain filling rate increases proportionately to external sucrose concentration up to about 100 mM (1,18). Sucrose uptake and starch synthesis by isolated wheat endosperm in both long-term (13) and short-term (19,26) experiments is responsive to sucrose concentration up to 150 mm, much higher than is found in endosperm cavity sap. In intact plants, Jenner and Rathjen (23) found that, within a given variety, grain filling rate shows a linear correlation with grain sucrose content.…”

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Accumulation and Conversion of Sugars by Developing Wheat Grains

Fisher¹,

Gifford²

1987

Plant Physiol.

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The extent to which wheat grain growth is dependent on transport pool solute concentration was investigated by the use of illumination and partial grain removal to vary solute concentrations in the sieve tube and endosperm cavity saps of the wheat ear (Triticum aestivum L.). Shortterm grain growth rates were estimated indirectly from the product of phloem area, sieve tube sap concentration, and 32p translocation velocity. On a per grain basis, calculated rates of mass transport through the peduncle were fairly constant over a substantial range in other transport parameters (i.. velocity, concentration, phloem area, and grain number). The rates were about 40% higher than expected; this probably reflects some unavoidable bias on faster-moving tracer in the velocity estimates. Sieve tube sap concentration increased in all experments (by 20 to 64%) with a concomitant decline in velocity (to as low as 8% of the initial value). Endosperm cavity sucrose concentration also increased in all experiments, but cavity sap osmolality and total amino acid concentration remained nearly constant. No evidence was found for an increase in the rate of mass transport per grain through the peduncle in response to the treatments. This apparent unresponsiveness of grain growth rate to increased cavity sap sucrose concentration conflicts with earlier in vitro endosperm studies showing that sucrose uptake increased with increasing external sucrose concentration up to 150 to 200 millimolar.In a general sense, the rate of transport into growing tissues and storage organs ('sinks') is clearly dependent on the availability of assimilates. In practice, however, the idea of 'assimilate availability' and its relationship to transport rates has been difficult to quantify. In terms of assimilates supplied to sinks by vegetative portions of the plant, an appropriate measure of their availability might be the concentration and composition of organic nutrients in the sieve tube sap, but this information is rarely available, particularly in comparing different treatments. For developing embryos, which must absorb their solutes from an apoplastic space, another measure of assimilate availability might be the concentration ofnutrients in the adjoining apoplast, such as the endosperm cavity sap of cereal grains. These two measures of assimilate availability are presumably related but,

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Starch deposition in storage organs and the importance of nutrients and external factors

Kosegarten

Mengel

1998

J Plant Nutrition & Soil

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Starch is an important agricultural product deposited in vegetative and reproductive storage organs (sinks) of various crop species. Starch yield may in some cases be limited by photosynthesis, i.e. source‐limited. This is particularly true for starch synthesized in potato tubers. Here, the physiological sink is characterized by a symplastic phloem unloading path. In reproductive storage tissues (seeds), however, photosynthates must pass the apoplast on their path from phloem unloading to the storage cell. In cereal grains, phloem unloading of sucrose and poslunloading processes rather than photosynthesis may thus control starch synthesis (sink‐limited). Various limiting steps along the path of photosynthate movement from the phloem to the storage cells are considered. The primary organic carbon for starch synthesis is sucrose. Sucrose delivered to the storage cell is metabolized to UDPglucose and fructose by means of sucrose synthase activity. Concerning sucrose breakdown the role of cell‐wall bound invertase is not well defined. Competition for UDPglucose consumed for growth or storage may be a crucial process in photosynthate partitioning. High starch yields of crops require an undisturbed growth of the sink organ and an optimal filling of sink amyloplasts with starch. The most important form of organic carbon imported into amyloplasts of storage organs (cereal grain and potato tuber) and used for starch synthesis is glucose 1‐phosphate. It is still to be clarified whether the rate of glucose 1‐phosphate absorption has a direct impact on starch yield. In cereals, the total amount of starch accumulated depends significantly on the duration of grain filling. Ample nutrient and water supply at the post‐anthesis stage prolongs the period of grain filling and hence favours starch production. High temperature reduces the activity of soluble starch synthase with negative consequences for starch accumulation. The biochemical and physiological implications of these stress factors are discussed. Recently, successful transgenic manipulations of starch synthesis in crop plants have increased starch yield.

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Accumulation and conversion of sugars by developing wheat grains. 3. Non‐diffusional uptake of sucrose, the substrate preferred by endosperm slices

Cited by 28 publications

References 14 publications

Heat Inactivation of Starch Synthase in Wheat Endosperm Tissue

Heat Inactivation of Starch Synthase in Wheat Endosperm Tissue

Accumulation and Conversion of Sugars by Developing Wheat Grains

Starch deposition in storage organs and the importance of nutrients and external factors

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