Studies on the Postharvest Physiology and Storage of Citrus Fruit
VIII. Metabolism of Citrate-14C and Glucose-14C in Satsuma Mandarin Fruit during Storage
1977 Volume 46 Issue 3 Pages 375-379
Details
1977 Volume 46 Issue 3 Pages 375-379
To study the organic acid and carbohydrate metabolism of mandarin fruit after harvest, the metabolic processes of citrate-1, 5-14C (pH 3.49), glucose-1-14C (pH 7.0; G-1-14C) and glucose-6-14C (pH 7.0; G-6-14C) which were injected with a disposable syringe into a segment through the rind of the fruit were investigated during storage at 7±3°C for 50 days after injection.
1. The injected citrate-14C was incorporated into 14CO2 immediately after injection. The cumulative radioactivity of respired 14CO2 continued to increase rapidly and attained to 28.8% of total radioactivity after 10 days and 33.5% after 50 days. Meanwhile, the cumulative radioactivity of 14CO2 from G-1-14C and G-6-14C continued increase slowly and attained to 6.5% and 6.3% of total activity of the substrates after 50 days, respectively.
2. The rate of cumulative radioactivity of 14CO2 from the injected G-6-14C and G-1-14C was 0.34 for subsequent 2 days, 0.63 for 5 days, 0.68 for 10 days and 1.02 for 50 days after injection, respectively. These results may show that the hexose monophosphate pathway is the major pathway in the early stages of glycolysis of injected glucose and the glycolysis tends to shift to the Embden-Meyerhof Parnas pathway from HMP pathway in the latter period of the experiment.
3. The injected citrate-14C could be incorporated rapidly into the carbohydrates, amino acids, proteins and pectic substances. There remained only a half amount of the substrate in the anionic fraction after 10 days. The metabolic activity of glucose-14C was considerably low as compared with that of citrate-14C. Therefore, the remaining of glucose-14C in the neutral fraction was about 80% after 50 days. The rate of incorporation into organic acid-14C and amino acid-14C from the moiety of injected glucose-14C attained to about 20% of total radioactivity of the ethanol soluble fraction at the end of experimental period.
From these results, it may be concluded that the rate of turnover of citric acid in mandarin fruit can be considerably high, even after harvest.
