Effect of Temperature on Starch Synthesis in Potato Tuber Tissue and in Amyloplasts

Abstract

A sharp temperature optimum is observed at 21.5°C when the incorporation of ["4Clsucrose into starch is measured with discs cut from developing tubers of potato (Solanum tuberosum L. cv Desiree). By contrast, increasing temperatures over the range 9 to 31°C only enhance release of '4C to respiratory CO2 and incorporation of '4C into the ethanolsoluble fraction. By comparison, starch synthesis in discs from developing corms of cocoyam (Colocasia esculenta L. Schott) is increased by raising the temperature from 15 to 35°C. The significance of a relatively low temperature optimum for starch synthesis in potato is discussed in relation to the yield limitations imposed by continuously high soil temperatures. Amyloplasts isolated from protoplasts prepared from developing potato tubers contain activities of alkaline pyrophosphatase, NADdependent glyceraldehyde-3-phosphate dehydrogenase, fructose-1,6-bisphosphatase, and phosphoglucomutase in addition to ADP-glucose-pyrophosphorylase, starch phosphorylase and starch synthase. Cell-free amyloplasts released by thinly slicing developing potato tubers synthesize starch from I'4Cltriose-phosphate generated from phosphate in the reaction medium. This starch synthesis is inhibited by addition of 10 millimolar inorganic phosphate and requires amyloplast integrity, suggesting the operation of a triose-phosphate/inorganic phosphate exchange carrier at the amyloplast membrane. The temperature optimum at 21.5°C observed with tissue discs is not observed with amyloplasts.The yield of potatoes in the warm tropics is limited by the continuously high soil temperatures (1). Growth of the potato tuber is closely linked to starch synthesis, and physiological studies with whole tubers still attached to the parent plant have indicated that higher temperatures could reduce yields by inhibiting starch synthesis in the tuber (17,24,28,33). However, interpretation ofthe results of these studies has been complicated by the possible influence of a temperature-dependent redistribution of plant growth regulators, especially gibberellin ( 17,28), and the sensitivity of starch synthesis per se to higher temperatures has remained unknown. Thus, the present work was carried out to determine the temperature optimum for starch synthesis in excised potato tuber tissue supplied with sucrose and in cellfree amyloplasts supplied with triose-P. were taken from plants grown in Reading, either in the open ground during the summer or in a glass house with supplementary heating (15-20°C) and lighting (13 h daylength) during winter. Developing corms of cocoyam (Colocasia esculenta L. Schott) were taken from plants grown under natural lighting in a heated glasshouse. Tubers and corms were washed, surface sterilized, and peeled before use. In the glasshouses, plants were grown in potting compost contained in I0-L polythene tubs and watered daily. MATERIALS AND METHODSPreparation of Discs and Measurement of Sucrose Uptake into Different Fractions. Potato tubers or cocoyam corms were sliced to 1 mm thickness,...

Starch synthesis in amyloplasts purified from developing potato tubers

“…were not intact, and implied that triose phosphates were the substrates of starch synthesis (Mohabir and John, 1988), or which were even more enriched in mitochondria than amyloplasts (Schott et al, 1995). The use of protoplasts made from suspension cultures of potato (Kosegarten and Mengel, 1994) exposure to cellulolytic enzymes.…”

Transport Processes and Corresponding Changes in Metabolite Levels in Relation to Starch Synthesis in Barley (Hordeum vulgare L.) Etioplasts

“…Differences between starch synthesis under in vivo conditions and in isolated amyloplasts had been also obtained using sliced potato tubers and isolated plastids (18). In addition, the rate of starch synthesis might be higher at earlier stages of tissue development.…”

High-Temperature Perturbation of Starch Synthesis Is Attributable to Inhibition of ADP-Glucose Pyrophosphorylase by Decreased Levels of Glycerate-3-Phosphate in Growing Potato Tubers1

“…However, several studies provide evidence that the reduced carbon import into potato tubers at high temperature is attributable to reduced Suc mobilization in the tuber itself, and not just to a shortage of photosynthate supply (Kraus and Marschner, 1984;Mohabir and John, 1988;Wolf et al, 1991). There are two lines of evidence.…”

“…First, inhibition of potato tuber growth at elevated soil temperatures is accompanied by increased Suc levels in the tubers as well as in the leaves, indicating a block of Suc breakdown and starch synthesis in the tubers (Wolf et al, 1991;Midmore and Prange, 1992). Second, compared with other cellular processes such as respiration, which increase with temperature up to 40°C, the optimum temperature for starch synthesis is relatively low (Mohabir and John, 1988). Shortterm experiments with […”