Relationship between increase in water content and cell wall composition in fig [Ficus carica] syconia during enlargement and ripening

To elucidate the mechanism of enlargement in fig syconia, changes in contents of water and cell wall polyuronides in fruitlets and fruit receptacles of 'Masui Dauphine' and 'Houraishi' (Ficus carica L. var. hortensis Shinn) second crops were investigated during ripening. Cell wall polyuronides were sequentially extracted from ethanol insoluble materials of each part with water, hot-water, EDTA and KOH solutions, then the content of uronic acid in each fraction was analyzed. Furthermore, changes in settling volume in water and water-holding capacity of water-insoluble solids (WIS) in each part were determined. In both cultivars syconia, the fresh weights of the fruitlets and fruit receptacles at harvest time showed an increase nearly 4 times as much as those at 70th day after bearing. Around 80-90 % of the weights increased in each part during ripening were due to an increase in water. The polyuronides contents per unit weight in the fruitlets and fruit receptacles decreased rapidly in the hot-water- and EDTA-soluble fractions and increased in the water-soluble fractions in two weeks before harvest. The whole polyuronides contents, on fresh weight basis, in each part increased largely in the water-soluble fractions during ripening with reverse relationship of those in the EDTA-soluble fractions. The WIS contents per unit weight in the fruitlets and fruit receptacles decreased markedly at harvest time, while the whole WIS contents, on fresh weight basis, changed very little during ripening. The settling volume in water and water-holding capacity of WIS increased largely at harvest time, especially in the fruit receptacles. It was suggested that rapid increase of water in the fruitlets and fruit receptacles during enlargement and ripening of fig syconia was related to solubilization of pectic substances and increase in swelling and water-holding capacity of WIS in cell wall