Tadaaki Fukushima

Chilling-injury in cucumber fruits. I. Effects of storage temperature on symptoms and physiological changes

Abstract Cucumber fruits transferred to a warm temperature after chilling displayed various symptoms of chilling-injury. In cucumbers chilled to 0°C, vertical fine wrinkles and/or shallow pitting was observed, while after chilling to 5°C deep pitting and/or surface depressions were apparent. Moreover, in the 0°C fruit compared with 5°C fruit, a higher 210 264 mμ UV absorption ratio of leakage substances during chilling was observed. These results suggest that the causes of chilling-injury in the 0°C and 5°C fruit are distinct from one another. Weight loss after chilling, the amount of leakage substances, the exudate content from the cut surface of the fruit, redox potential, titratable acidity and respiratory activity were also checked after periods of chilling of 3 to 15 days.

Chilling-injury in cucumbers. V. Polysaccharide changes in cell walls

Abstract A decline in the hot-water-soluble pectin and an increase in the hot-water-insoluble pectin were observed when cucumber fruits were subjected to chilling temperatures. Infrared absorption spectra revealed the presence of highly esterified carboxyl groups in the soluble pectin, and of free carboxyl groups in the insoluble pectin. An increase of the insoluble pectin during chilling was also found in other chilling-sensitive plants. From these results it is suggested that a de-esterification of pectin and the concomitant increase of polymeric pectin takes place during chilling, making cell walls firmer, and that these pectic changes may be a characteristic common to a number of chilling-sensitive plants.

Chilling-injury in cucumber fruits. VI. The mechanism of pectin de-methylation

Abstract By incubating the homogenate of cucumber fruits in vitro, pectin de-methylation was considerably accelerated especially at near neutral pH. Histo-chemical observations based on detection of SH-protein present in sieve tubes, revealed that the cell walls of the fruits chilled at 0°C for 3 days contained the tube constituents, in which pectinmethylesterase was also found. The esterase of the tubes was cold-labile. All the esterases present in a fruit were activated by an addition of ascorbic acid, a reducing agent. The set of these results, together with our previous papers, suggests that in cucumber fruits chilling may at first break the plasmalemma of sieve tubes, whose exudate outflows into the cell walls of tissue cells. The subsequent contact between the tube esterase and wall pectin results in the pectin de-methylation, which makes elastic cell walls rigid and fragile. This ultimately leads to occurrence of water-stress injury. A decrease of redox potential in the chilled fruits may serve for raising the activity of the cold-labile tube esterase.

Chilling-injury in cucumber fruits. IV. The analogy between osmotic-stress injury and chilling-injury

Abstract At warm temperatures, young cucumber fruit with rigid cell walls was found to suffer osmotic-stress injury when hydrated or dehydrated. The osmotic-stress injury of hydrated fruit was similar to chilling-injury of cucumber fruit stored at 5°C, whereas the stress injury of dehydrated young fruit appeared similar to injury of fruit chilled to 0°C. In contrast, adult fruit, with soft cell walls, did not develop osmotic-stress injury. On the basis of these results, together with previous reports, it is proposed that cell wall rigidity and water stress in the fruit are the direct causes of chilling-injury.

Chilling-injury in cucumber fruits. III. Dynamic changes of osmotic quantities and the importance of cell wall rigidity

Abstract In cucumber fruit transferred from controlled chilling, the lowest turgor pressure was observed in the surface and sub-surface tissues of those fruits chilled at 0°C, which suffer from a contraction of the protoplast. The highest turgor pressure was noted in the flesh tissue of the 5°C fruit, where there is a breakage of plasma-membrane. From these results, it is suggested that dehydration or hydration of the chilled cells causes a shrinkage or breaking of plasma-membrane, respectively. Moreover, because the cell walls in chilled fruit become rigid at the same time as the onset and development of chilling-injury, the importance of cell wall rigidity in relation to chilling-injury is discussed.

Chilling-injury in cucumber fruits. II. Chemical analyses of leakage substances and anatomical observation of symptoms

Abstract From the chemical composition of leakage substances, it was concluded that there was greater leakage of micro-molecule components in cucumber fruits which had been chilled to 0°C than in fruit chilled to 5°C. However, leakage of macro-molecule components was greater in the 5°C fruit than in the 0°C fruit with longer periods of storage. These results suggest that the plasmalemma develops leakage in the 0°C fruit, whereas there is membrane breakage in the 5°C fruit. Microscopic observations support this assumption.

The relation between water stress and the climacteric in respiration of some fruits

Abstract Respiration rate, turgor pressure, osmotic pressure and suction pressure were checked periodically after harvest with bananas, pears, apples, tomatoes and cucumbers. There were great differences among species in the courses of osmotic and suction pressure changes, but those of the resulting turgor pressure appeared to be basically similar. Moreover, there was a relatively close relation between respiration rate and turgor pressure.