Abstract
“Kokuhen” injury (a physiological disorder in which the fruit skin turns black) often appeared after harvesting Japanese pear (cultivar ‘Shinsui’) maturing in midsummer. The purpose of this report is to make clear the relationship between“Kokuhen” injury and the storage temperature, to reduce this disorder by the application of chemicals, and to investigate biochemical aspects such as the alteration of polyphenol oxidase activity and membrane permeability with the disorder.
1. The symptom of injury did not appear when fruit harvested at optimum maturity were stored at a range of 1° to 10°C.
The symptom began to increase above 20°C, and appeared rapidly and severely at 30° to 35°C. The whole fruit skin turned black completely within 36hrs of storage at 50°C. However, the symptom was restricted transiently at 40°C.
2. The injury was typically restricted by dipping fruit in 1, 000ppm IAA solution. A solution of 1, 000ppm GA3, also, was effective to protect it.
3. There was no difference in optimum pH or Km value of polyphenoloxidase activity between injured fruit and healthy fruit. Moreover, the activity did not rise with increased injury.
4. The leakage of potassium from fruit slices increased gradually during incubation from 2 to 3 days before the appearance of injury, and rose more as the injury became worse. By compartment analysis (2, 11), the leakage rate of potassium from the vacuoles of fruit flesh was very slow at 1° to 10°C.
However, it rose rapidly above 30°C. This enhancement of rate paralleled the intensity of injury. The leakage rate of potassium from the vacuoles was also reduced transiently at 40°C, and the appearance of injury was restricted.
Thus, “Kokuhen” injury of Japanese pear is suggested to be caused by loss of cellular compartmentation, attributed to an increase in permeability of the tonoplast.
