Histological Observations on the Chilling Injury of Cucumber Fruit during Cold Storage

Histological changes were observed during development of external symptoms of chilling injury in cucumber fruirs (cv. Tokiwa Shin No. 2) stored at 4°C.Main external symptoms of chilling injury of cucumber fruits were pitting and whitish leakage on their surfaces. Pitting tended to appear at the lower relative humidity of 80-95% in cold storage, while leakage was inclined to occur at the higher relative humidity above 95%.Before appearing of pitting, cell flattening following plasmolysis originated from the parenchyma cells adjacent to substomatal chamber. Flattened cells increased in parallel with the epidermis and to the inner cell layers. Epidermal cells also flattened, after flattening of parenchyma cells progressed to the depth of 8-10th layers under the epidermis. At this stage depression occurred around stoma and pittings were observed externally. At more advanced stage of pitting, the areas of cell flattening around respective stoma extended and joined mutually, and also reached to the depth of 15-20th layars under the epidermis.Before oozing of whitish leakage, parenchma cells adjacent to substomatal chamber collapsed with their call walls. However, no plasmolysis and cell flattening were observed unlike pitting. At more advanced stage, epidermal cells collapsed with more than 7-8 layers of parenchyma cells under epidermis, and whitish leakage derived from cellular collapses oozed to the fruit surface through stomata and also to intercellular spaces.At the incipient stage of pitting, nuclei of cells shrank, and then collapsed in the epidermis and immediately underlying parenchyma around stoma. On the other hand, nuclei in the above tissues apart from stoma, and those of parenchyma cells in the internal fleshy tissue shrank accompanying with plasmolysis, after temporary swelling immediately before appearing of the external symptoms.