福岡県農業総合試験場研究報告

イチジク果実の肥大・成熟に伴う水分含量の増加と細胞壁成分との関係

［摘要］イチジク果実の肥大機構の解明を進めるため、‘桝井ドーフィン’と‘蓬莱柿’の秋果の成熟に伴う小果、果托内の水分含量と細胞壁のポリウロニド含量の変化を調査するとともに、水不溶性固形物（ＷIＳ）の水中沈定体積と最大抱水量を測定して細胞壁の保水能の変化について検討を行った。両品種とも、収穫期の果重は結果70日後に比べて４倍近くに増加した。成熟に伴う重量増加量の80～90％は水分の増加によるものであった。小果、果托の単位重量当たりのポリウロニド含量は、収穫前の２週間に熱水およびＥＤＴＡ可溶性画分で急激に減少し、水可溶性画分で増加した。小果、果托の重量から換算した部位別のポリウロニドの総量は、収穫期に水可溶性画分で急激に増加するとともにＥＤＴＡ可溶性画分で減少した。ＷＩＳの小果、果托の単位重量当たり含量は、収穫期に急激に減少した。しかし、小果、果托の重量から換算したＷＩＳの総量の成熱に伴う変化は小さかった。ＷＩＳの水中沈定体積と最大抱水量は、小果、果托とも収穫期に増加し、特に果托での増加が顕著であった。イチジク果実の肥大、成熟に伴う小果、果托内の急激な水分含量の増加には、細胞壁におけるペクチン質の可溶化と水不溶性成分のかさ形成能および保水能の増大が関係していることが示唆された。

［キーワード：イチジク果実、肥大、成熟、水分含量、細胞壁成分］

　 Relationship between Increase in Water Content and Cell Wall Composition in Fig Syconia during Enlargement and Ripening.YAHATA Daijirou and Hitoshi NOGATA (Fukuoka Agric. Res. Cent., Chikushino, Fukuoka 818-8549, Japan) Bull. Fukuoka Agric. Res. Cent., 19: 76 - 80(2000)

　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 wallpolyuronides 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 ofwater-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 eachpart 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.