Varietal differences and changes in cell wall composition in ripening fig fruits

Abstract

To elucidate the varietal differences in cell wall composition of fig fruits at harvest, the uronic acid and neutral sugar contents in the syconia of Caprifig 'VC-180' (Ficus carica L. var. intermedia Shinn x F. carica L. var. sylvestris Shinn), San Pedro type 'King' and 'San Pedro White' (F. carica L. var. intermedia Shinn) and common figs 'Masui Dauphine' and 'Houraishi' (F. carica L. var. hortensis Shinn) were analyzed. In addition, the changes in cell wall composition of ripening 'Masui Dauphine' fruits were investigated, comparing uronic acid and neutral sugar contents in the syconia exhibiting 10, 50, and 100% colored peel. Cell wall polysaccharides were sequentially extracted from ethanol insoluble materials of pistillate flowers with water, hot-water, EDTA, KOH (hemicellulose fraction), and H2SO4 (cellulose fraction) solutions. 1. In the water fractions, the varietal difference in cell wall composition was very small. The total sugar contents, including uronic acid and neutral sugar, in the hot-water, EDTA, hemicellulose, and cellulose fractions were significantly highest in the syconia of 'VC-180'. Except for 'VC-180', the difference in neutral sugar contents in the cellulose fractions was largest among other cultivars. 2. The uronic acid contents per unit weight in the water fractions, extracted from 'Masui Dauphine' syconia during ripening, became higher in the order of 50, 100, and 10% colored peel, but there was little difference in the neutral sugar contents in the same fractions. In the hot-water and EDTA fractions, the uronic acid contents per unit weight decreased with color development; therefore, the total sugar contents from pectic substances likewise decreased. In the hemicellulose and cellulose fractions, both the uronic acid and neutral sugar contents per unit weight decreased with color development. 3. The cell wall composition per fruit of 'Masui Dauphine' was different from that per unit weight, because the ripening fruits increased in weight. As the percentage of coloring in the peel increased, the uronic acid contents per fruit increased markedly in the water fractions and decreased in the hot-water and EDTA fractions; the neutral sugar contents per fruit increased in the water and hot-water fractions. However, there were no differences in the total sugars per fruit derived from the pectic substances or in the uronic acid, neutral sugar, and total sugars per fruit derived from the hemicellulose and cellulose fractions during the ripening process.