Abstract
How the cell wall constituents in Japanese pear mealy fruit (Pyrus serotina Rehder culta Rehder, cvs. Chojuro, Kikusui, 92-7, _??_-33) and“Ishinashi”fruit (cv. Chojuro) differ from fruit showing hardly both symptoms (cvs. Nijisseiki, Hosui, 93-3) was shown through analyses of cell wall polysaccharides and their constituent monosaccharides, and cell wall-degrading enzyme activities.
Cell wall polysaccharides were fractionated into water-soluble carbohydrate (9_??_13%), NaClO2-soluble carbohydrate (3_??_5%), EDTA-soluble carbohydrate (below 2%), acid-soluble hemicellulose (23_??_39%), alkali-soluble hemicellulose (16_??_21%) and cellulose (25_??_36%). The polysaccharides were composed of glucose (35_??_43%), uronic acid (26_??_31%), xylose (11_??_19%), arabinose (8_??_13%), galactose (4_??_7%), rhamnose (1_??_2%), mannose (below 1%) and fucose (below 1%).
In mealy fruit, the degradation of acid-soluble hemicellulose in the middle lamella was more prominent than in the control fruit, with the former showing the higher activity of polygalacturonase. The degradation of the cellulose component in the mealy fruit was restricted compared with the control fruit because the rise in endocellulase (neutral form) activity was suppressed. This suggests that the flesh of mealy fruit consists of a weaker attachment of cells and a more rigid cell wall structure than the control fruit.
In“Ishinashi”fruit, the degradation of acid-soluble hemicellulose and cellulose components was more restricted than in the control fruit. This restriction was also supported by the result that the activities of polygalacturonase, endocellulase and exocellulase were lower than in the control fruit. This suggests that the flesh of the“Ishinashi”fruit contains a tighter attachment of cells and a more rigid cell wall structure than that of the control fruit.
It is suggested that there are some varietal differences in the cellulase and polygalacturonase activities and in the compositions of the cell wall polysaccharides.
