|Solomos, Theophanes - UNIV OF MD|
Submitted to: Book Chapter
Publication Type: Book / Chapter
Publication Acceptance Date: March 20, 2004
Publication Date: May 5, 2005
Citation: Solomos, T., Mattoo, A.K. 2005. Starch-sugar metabolism in potato (solanum tuberosum) tubers in response to temperature variations. In: Razdan, M., Mattoo, A. Genetic Improvement of Solonaceous Crops: Volume I. Enfield, NH, Science Publishers, Inc. pp. 209-234. Interpretive Summary: Potato tubers accumulate starch as the main complex sugar. Starch gets converted into simple sugars during low temperature storage. Cold storage of potatoes is preferred because it inhibits sprouting, decreases losses due to microbial spoilage and prevents weight-loss caused by dehydration. However, the increase in simple reducing sugars during low temperatures negatively affects processing quality of the tubers. This manuscript is a synthesis of studies on, and regulation of, enzymes - protein biocatalysts - involved in the starch-sugar interconversion and temperature effects in tubers. Also presented is a scenario that could be used in future as a strategy to inhibit sugar accumulation during low temperature storage and preserve the processing quality of potato tubers. This manuscript is of use to scientists and students studying potato biology, and to potato industry.
Technical Abstract: In potatoes low O2 (1.52 kPa) totally suppresses the rise in CO2 output, the rate of which remains at the same levels as that attained by tubers that have been held in air at 1oC for two days. Low O2 does not prevent the decrease in cytochrome oxidase observed in tubers held in air at 1oC. Nevertheless, it suppresses the induction of the alternative oxidase, resulting in a diminution of the total mitochondrial O2 uptake (Zhou and Solomos, 1998). Hypoxia strongly inhibits the accumulation of sugars during sweetening at 1oC. This is accompanied by the suppression of the rise in the activities of SPS, invertase and amylases. In addition, it suppresses the induction of acid invertase transcripts and the new amylase isoforms. On the other hand, it has no effect on the activity of starch phosphorylase (Zhou and Solomos, 1998). Hypoxia (2.03 kPa O2) inhibits the decrease in sugars during reconditioning of tubers that have been held at 1oC for 28 days and then transferred to 10oC. Furthermore, it prevents the rise in respiration. Yet low oxygen does not prevent the decline in the activities of SPS and invertase (Illeperuma et al., 1998). It is therefore probable that hypoxic treatment may alter the pattern of changes during the conversion of starch to sugars at low temperatures, as well as during the reverse conversion at 10oC. Thus, hypoxia inhibits the induction and/or enhancement of enzymatic activities in response to the temperature treatments but has no effect on enzymes that are either constitutively expressed, such as starch phosphorylase, or that decline in response to treatments, such as cytochrome oxidase, SPS and invertase. In this respect, hypoxic treatments may be employed to discern the regulatory steps in the sucrose-starch inter-conversion during storage of potato tubers. Experimental results with growing intact potato tubers and slices show that a decrease in O2 concentration to levels that do not restrain mitochondrial terminal oxidases results in a decrease in starch synthesis (Tiessen et al., 2002; Geigenberger, 2003).