ISHS Acta Horticulturae 343: Physiological Basis of Postharvest Technologies
CHILLING-INDUCED CHANGES IN PHENYLALANINE AMMONIA-LYASE, PEROXIDASE, AND POLYPHENOL OXIDASE ACTIVITIES IN CITRUS FLAVEDO TISSUE |
| Authors: | M.A. Martínez-Téllez, M.T. Lafuente |
| Abstract:
Pitting and staining in citrus fruits are caused by various stresses, such as chilling. Polyphenol metabolism has often been thought to be involved in necrogenesis. Since phenylalanine ammonia-lyase (PAL), peroxidase (POD) and polyphenol oxidase (PPO) are involved in the metabolism of phenolic compounds and in the development of a number of physiological disorders, we have undertaken to study the effect of low temperature storage (1.0, 2.5, and 5C) (chilling temperatures) and of a non-chilling temperature (10C) on the activation of these three enzymes in flavedo tissue of two different citrus cultivars. Orange fruits, cultivar Navelina (Citrus sinensis L. Osbeck), were stored 60 days at 1.0, 2.5 and 10C. Mandarin fruits, cultivar Fortune (Citrus reticulata), were stored 25 days at 2.5, 5 and 10C. Pitting and staining symptoms did not occur at 2.5 or 1.0C in Navelina flavedo tissue even after 60 days storage. In Fortune fruits, however, chilling symptoms began to appear after 8 days storage at 2.5 or 5C. After 14 days, 72% of fruits kept at 2.5C and 62% of fruits kept at 5C already showed chilling symptoms. No correlation was found between the development of chilling symptoms and the changes in POD and PPO activities in both cultivars. The susceptibility of Fortune fruits to chilling paralleled its capacity for the activation of PAL in response to low temperature. In fruits held 25 days at 10C no symptom appeared and PAL activity decreased from 27 to 3 mμmol cinnamic acid/hr/g fresh weight. PAL activity and chilling symptoms in fruits stored at 2.5C were higher than in fruits stored at 5C. After 25 days, PAL activity of fruits kept at 2.5C was 157 mμmol cinnamic acid/hr/g fresh weight whereas at 5C it was 112 mμmol cinnamic acid/hr/g fresh weight. These results indicate that the difference in susceptibility to chilling injury between the two cultivars are more likely related to PAL activity than to PPO or POD activity. | |
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