キュウリ果実の低温障害に伴う表皮構造の変化

Abstract

Morphological changes in cucumber fruit‘Megami 2 gou’and‘Horai’associated with chilling injury were studied by scanning electron microscopy (SEM).1. Stomata, trichomes, scars of trichomes, warts with or without spines and epidermal cells with thick cell walls were observed on fruit surfaces immediately after harvest. Many of trichomes, warts and spines were found to be detached from epidermal tissue. Since these appendages were very fragile, they became detached from epidermal tissue during pre- and post-harvest handling, and preparation for SEM. The wart (multicellular hair appendages) had spines consisting of 5 cell parts. There were stripped epidermal tissues under part of the detached warts, and many scars on epidermal tissues. These injured parts may be easily infected by decay organisms during storage.2. Morphological changes were found on the fruit surfaces after storage at 5°C, while there were no notable changes on the epidermal tissues of fruit stored at 20°C. Slightly wrinkled epidermal tissues were found on the fruit surfaces after storage at 5°C for 3 days. When visible symptoms of pitting began to be seen on a surface, several small pores (about 70-130μm in diameter) were observed in sunken areas of epidermal tissues. There were also several cracks around the stomata and sunken guard cells in the chilling-injured fruit stored at 5°C.3. mucilage leaked out from the epidermal tissue where several small pored (about 10μm in diameter) were found after long term storage at 5°C. However, we could not clarify how these small pores were produced. Some pitted areas of fruit stored at 5°C for more than 10 days were covered with a thick layer of hyphae. Judging from the observations by SEM, the pitting associated with chilling injury of cucumber fruit may have occurred as a combination of the following factors: a) cracks around the stomata, b) collapse of inner tissues including the parenchyma tissues, c) sinking of epidermal cells near the stomata and stimulation of transpiration from pores, and e) deposit of mucilage.