ナツミカン果実貯蔵中の低温障害に関する生理学的研究-1-

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Citrus fruits such as oranges, lemons, and grapefruits suffer physiological injury when subjected to low but non-freezing storage temperatures. On natsudaidai fruits, of which production is a considerable amount among Japanese citrus fruits, there has been little available report concerning low temperature storage. Our preliminary experiments, purported to establish optimum storage temperature, showed occurrence of typical chilling injury on natsudaidai fruits. The present study was carried out to confirm this phenomenon in reference to its physiological aspects.(1) When natsudaidai fruits were stored at 1-1.5°C for two month or longer, chilling injury developed gradually. On the peel of chilled fruits brown pitting appeared and the fruits became susceptible to decay. Darkening of whole peel color was also found. Furthermore, prior to the appearing of visible injury during low temperature storage, the fruits increased susceptibility to microorganisms, and when transferred to 20°C severe decay took place rapidly. At 6°C, the fruits were stored without chilling injury and kept good external appearance for three months. At 13°C, half of fruits decayed during the storage of three months.(2) Respiration rate of fruits decreased with duration of storage at 6°C, showing the same tendency as ordinary citrus fruits. On the contrary, the respiration of fruits stored at 1°C exhibited continuous increase, and reached higher rate than that of the fruits at 6°C in the latter portion of storage period. When the fruits transferred from 1°C to 20°C, spur of carbon dioxide output was observed, and the degree of stimulation was more conspicuous with increasing exposure time at low temperature.(3) Respiration of flavedo tissue slices was measured at 30°C. Respiration rate of the slices prepared from 1°C-stored fruits was higher than that from 6°C- or 13°C-stored fruits especially in the latter portion of storage period. Respiratory quotient became lower than unity in the tissues from non-chilled fruits. However, at 1°C the RQ value remained at high level throughout the storage period.(4) Because the measurement was carried out with externally sound fruits, the results mentioned above suggest that abnormality of metabolism may have occurred in the healthy-appearing fruits during the 1°C storage.(5) Ascorbic acid content remained higher in the fruits stored at low temperature, indicating no relation to mechanism of chilling injury.(6) Potassium ion leakage from flavedo tissue slices suspended in water or sucrose solution was measured to detect the change of cellular permeability during the low temperature storage. However, no relation was found between the leakage and cause of chilling injury.(7) Prior to low temperature storage, a portion of fruits were treated with N6-benzyladenine, gibberellin, indoleacetic acid, and fruit wax. No effect was found to prevent the development of chilling injury with all chemicals used.
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ナツミカン果実貯蔵中の低温障害に関する生理学的研究-1-

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