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Effect of hypoxia on sugar accumulation, respiration, activities of amylase and starch phosphorylase, and induction of alternative oxidase and acid invertase during storage of potato tubers (Solanum tuberosum cv. Russet Burbank) at 1oC
The transfer of potato (Solanum tuberosum) tubers from 10 to 1°C was associated with an initial decline in the rate of CO2 output followed by a rapid increase reaching, within some 12 days, a peak which was about 3‐fold higher than at 10°C. Thereafter the rate of CO2 evolution declined gradually for the duration of the experiment. The specific rate of mitochondrial O2 uptake decreased initially, followed by a rise to a level similar to that of mitochondria prepared from tubers stored at 10°C. Low temperature decreased by 30% the capacity of the cytochrome pathway while it sharply increased the capacity of the alternative pathway. Sucrose was the first sugar to accumulate at 1°C, followed after a delay of 6‐7 days by glucose and fructose. Low temperature induced within 4‐5 days a rise in amylase activity which increased by 10‐fold after 30 days. The increase was reflected in only two out of four existing isoforms. In addition a novel isoform of amylase was detected later in storage. The induction and the accumulation of invertase mRNA and extractable activity followed the increase in sucrose but preceded that of hexoses. The activity of starch phosphorylase isoforms was not affected by temperature. There was a 3‐fold increase in chlorogenic acid at 1°C. Hypoxia strongly inhibited the accumulation of sugars and chlorogenic acid, the increase in the amylase activity, and the appearance of the novel isoform. Low O2 totally suppressed the induction of invertase mRNA and increased the capacity of the alternative oxidase. It did not, however, prevent the decrease in cytochrome capacity; neither did it affect the activity of starch phosphorylase isoforms.