The Comparative Study of Postharvest Physiology on Cultivars of Averrhoa carambola L.
Date Issued
2015
Date
2015
Author(s)
Sun, Yi-Lun
Abstract
The ripening behavior, i.e. climacteric or nonclimacteric, of carambola (Averrhoa carambola L.) is still a controversial issue. ‘Hong-Long’ and ‘Jing-Long’, two carambola varieties with discriminating ethylene production after harvest, were used to investigate their physiological changes during ripening at 20℃ in this research. The flesh firmness, titratable acidity, and total soluble solids of these fruits barely changed during ripening. ‘Hong-Long’ showed a surge of ethylene production (10.38 μL C2H4•kg-1•h-1) when fruit was fully ripe, which was tightly followed with flesh senescence (browning) and appearance of pathological lesions. On the other hand, ‘Jing-Long’ displayed a low and stable production of ethylene (1.43 μL C2H4•kg-1•h-1) in postharvest life. However, the physiological changes of ripening, time of ethylene peaks, as well as the enzymatic activities of ACC synthase (ACS) and ACC oxidase (ACO), the two key enzymes in ethylene biosynthetic pathway, were accelerated in these two fruits by exposure of 1000 µL•L-1 for 48 hours. In contrast, fumigation of 1 µL•L-1 1-methylcyclopropene (1-MCP), an ethylene action inhibitor, for 24 hours delayed ripening of the fruits tested. Therefore, it was unable to clearly characterize the ripening pattern(s) based only on the physiological parameters mentioned above. By utilizing RT-PCR strategy, two ACS and two ACO cDNA clones were obtained from fruit tissues of carambola. Real-time quantitative PCR analysis showed that low and stable expressions of AcACS2 and AcACO1 in these two varieties were found in early stage of fruit development; then decreased gradually after onset of ripening. Based on the facts that treatment of propylene suppressed these mRNA accumulations and that 1-MCP treatment up-regulated the expressions, AcACS2 and AcACO1 were considered as System 1 ethylene biosynthesis genes. Conversely, AcACS1 and AcACO2, mainly expressed in ripening stage, were induced by propylene and down-regulated by 1-MCP, which were classified as System 2 ethylene biosynthesis genes. Since System 2 ethylene biosynthesis genes existed in ‘Hong Long’ and ‘Jing Long’, these results suggested that carambola is a climacteric fruit.
Subjects
carambola,ripening,ethylene
ACC synthase
ACC oxidase,climacteric fruit
Type
thesis
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