Carbohydrate solutilization of tomato locule tissue cell walls: Parallels with locule tissue liquefaction during ripening

Carbohydrate solubilization and glycosidase activities were investigated in tomato ( Lycopersicon esculentum Mill. cv. Solar Set) locule cell walls to identity processes involved in the liquefaction of this tissue. Cell walls were prepared from the locule tissue of fruit at the immature green, mature green, and breaker stages of development. Enzymically active walls incubated in dilute buffer released high molecular mass pectins, oligomeric carbohydrate, and the neutral sugars rhamnose, glucose, galactose, arabinose, xylose, and mannose. The release was sustained for at least 50 h at 34°C and was inhibited more than 50% by 1 m M Hg²⁺. Pectins released from the cell walls of locule tissue at progressive stages of liquefaction were similar in molecular mass and showed no evidence of downshifts on a Sepharose CL–2B–300 column during prolonged incubation. A cell-free protein extract prepared from the locule tissue of mature-green fruit promoted a net release of polymeric and monomeric carbohydrates from high-temperature inactivated cell walls. Polygalacturonase activity was not detected in locule protein although glycosidases including β-mannosidase (EC 3.2.1.25), α- and β-galactosidases (EC 3.2.1.22–23), β-arabinosidase (EC 3.2.1.56) and β-glucosidase (EC 3.2.1.21) were present. Pectinmethylesterase (EC 3.1.1.1 1) activity was detected at the immature-green stage but declined to negligible levels in mature-green and breaker locule tissue. Parallels between the in vitro solubilization of carbohydrate from locule tissue cell walls and the changes occurring during locule liquefaction are discussed.