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  • Author or Editor: Caihong Zhang x
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Kiwifruit (Actinidia chinensis Planchon) is an economically important fruit, and its flowering and production are affected by the chill accumulation in winter. In this study, the chilling requirements of nine kiwifruit cultivars with three ploidy levels (diploid, tetraploid, and hexaploid) were analyzed by using the Dynamic Model, Utah Model, and chilling hours (CH) Model. The chilling requirements for vegetative budbreak of these kiwifruit cultivars were 24–55 chill portions (CP), 316–991 chill units (CU), and 222–853 CH, and the chilling requirements for floral emergence were 45–69 CP, 825–1336 CU, and 655–1138 CH. The chilling requirements for vegetative budbreak and floral emergence were significantly lower for diploid than hexaploid cultivars with tetraploid cultivars intermediate. Pearson correlation analysis indicated that ploidy levels were positively correlated with chilling requirement, with the cv of 0.74 and 0.82 for vegetative budbreak and floral emergence chilling requirements, respectively. In conclusion, these results provide some novel insights of kiwifruit varieties of various chilling requirements, which is beneficial for kiwifruit cultivar selection for different climates and environments.

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A full-length cDNA isolated from banana (Musa acuminata L. AAA group) fruit was named MaMDH, containing an open reading frame encoding 332 amino acids that represents the gene for cytoplasmic malic dehydrogenase (MDH). Sequence analysis showed that MaMDH shares high similarity with MDHs from castor bean (XP_002533463), tobacco (CAC12826), peach (AAL11502), and chickpeas (CAC10208). Real-time quantitative polymerase chain reaction (PCR) analysis of MaMDH spatial expression showed that it was expressed in all organs examined: roots, rhizomes, leaves, flowers, and fruits. The expression was the highest in flowers followed by the fruits and roots, whereas the rhizomes and leaves displayed the lowest expression levels. Real-time quantitative PCR revealed that MaMDH exhibited differential expression patterns in post-harvest banana fruits correlating with ethylene biosynthesis. In naturally ripened banana fruits, MaMDH expression was in accordance with ethylene biosynthesis. In accordance, for banana fruits treated with the ethylene analog 1-methylclopropene (1-MCP), MaMDH expression levels were inhibited and remained constant. After treatment with ethylene, MaMDH expression in banana fruits significantly increased with ethylene biosynthesis and peaked 3 days after harvest, which was 11 days earlier than that in naturally ripened banana fruits. These results suggest that MaMDH expression is induced by ethylene to regulate post-harvest banana fruits ripening.

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The banana, a typical climacteric fruit, undergoes a postharvest ripening process followed by a burst in ethylene production that signals the beginning of the climacteric period. Postharvest ripening plays an important role in improving the quality of the fruit as well as limiting its shelf life. To investigate the role of glutamate decarboxylase (GAD) in climacteric ethylene biosynthesis and fruit ripening in postharvest banana, a GAD gene was isolated from banana, designated MuGAD. Coincidently with climacteric ethylene production, MuGAD expression as well as the expression of the genes encoding the Musa 1-aminocyclopropane-1-carboxylate synthase (MaACS1) and Musa 1-aminocyclopropane-1-carboxylate oxidase (MaACO1) greatly increased during natural ripening and in ethylene-treated banana. Moreover, ethylene biosynthesis, ripening progress, and MuGAD, MaACS1, and MaACO1 expression were enhanced by exogenous ethylene application and inhibited by 1-methylcyclopropene (1-MCP). Taken together, our results suggested that MuGAD is involved in the fruit ripening process in postharvest banana.

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