樹上完熟栽培におけるウンシュウミカン果実のじょうのう膜の変化

Abstract

Physico chemical characteristics of segment membranes were studied in 'Miyagawa Wase' and 'Hayashi Unshu' as related to delayed harvest. In this study, we focused on segment membrane strength because it may be a critical factor in evaluating fruit quality.1. Large fruits had thicker segment membranes than did small fruits in both cultivars. Segment membranes of developing fruits, while yet immature, became thinner in 'Miyagawa Wase' but thicker in 'Hayashi Unshu'. The membrane became thinner, however, in 'Hayashi Unshu' as the fruits matured.2. Intrusive resistance as an index of segment membrane strength was higher in larger fruits. With the advancement of maturation, it became lower in 'Miyagawa Wase', whereas it showed little or no changes in 'Hayashi Unshu'.3. Some morphological differences in cells of the segment membrane between the two cultivars were observed in late February. The inner epidermal surface of the segment membrane showed some cracking in 'Miyagawa Wase'. Cell size of the outer epidermis of the segment membrane was larger in 'Hayashi Unshu' than in 'Miyagawa Wase'. Some digestion of the cell membrane was found in the latter.4. Cellulase and polygalacturonase activity in segment membrane increased more rapidly in 'Miyagawa Wase' than it did in 'Hayashi Unshu' after November as the fruit ma- tured. Contents of cellulose and total pectic substances in the segment membrane per 100 g whole fruit fresh weight decreased rapidly after December. This tendency was more pronounced in the smaller fruits of 'Miyagawa Wase'. Cellulose content on a dry weight basis of alcohol insoluble solids (AIS), in segment membrane, was lowest in the smaller fruits of 'Miyagawa Wase'.We believe that changes in segment membrane strength are caused, not only by digestion of the segment membrane through degradation of cellulose and total pectic substances, but also by qualitative changes of the membrane itself through the decrease of cellulose content as determined by AIS.