Collapse of Peroxide-Scavenging Systems in Apple Flower-Buds Associated with Freezing Injury |
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| Authors: | Kuroda Haruyuki; Sagisaka Shonosuke; Chiba Kazuhiko |
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| Institution: | 1 The Hokkaido National Agricultural Experiment Station Sapporo, 062 Japan
2 The Institute of Low Temperature Science, Hokkaido University Sapporo, 060 Japan |
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| Abstract: | Changes in the metabolic activities of peroxide-producing systemsand peroxide-scavenging systems after freezing and thawing inflower buds of the apple, Malus pumila Mill., were studied withspecial reference to freezing injury. In flower buds of the‘McIntosh’ apple that were frozen below lethal temperatures,the activity of NADH-Cyt c reductase (EC 1.6.99.3
EC]
), one of theenzymes in the electron-transport chains that are related tothe peroxide-producing systems, decreased slightly, while thatof Cyt c oxidase (EC 1.9.3.1
EC]
) hardly changed. By contrast, theactivities of glucose-6-phosphate dehydrogenase (EC 1.1.1.49
EC]
),dehydroascorbate reductase (EC 1.8.5.1
EC]
) and ascorbate peroxidase(EC 1.11.1.11
EC]
), which are involved in the peroxide-scavengingsystems, decreased to very low levels. The activity of glyceraldehyde-3-phosphatedehydrogenase (EC 1.2.1.12
EC]
) also decreased markedly. However,little change was observed in the activities of hexokinase (EC2.7.1.1
EC]
), glucosephosphate isomerase (EC 5.3.1.9
EC]
), glutathionereductase (EC 1.6.4.2
EC]
) and glutathione peroxidase (EC 1.11.1.9
EC]
).Examination of substrates involved in the peroxide-scavengingsystems revealed that the levels of glucose-6-phosphate andfructoses-phosphate decreased to approximately 10–4 to10–5 M and 10–5 M, respectively, and the levelsof GSH decreased to about 10–5 M or became barely detectable.A decrease in the levels of GSSG also occurred while levelsof ascorbate rose slightly. Similar results were observed withflower buds from ‘Starking Delicious’ and ‘Jonathan’apple trees. These results suggest that the freezing injury to apple flower-budsis closely related to the collapse of the peroxide-scavengingsystems that are coupled with the pentose phosphate cycle. Theresults also suggest that the dysfunction of these peroxide-scavengingsystems is caused by H2O2, which may be produced during freezingand thawing. (Received March 14, 1992; Accepted June 5, 1992) |
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