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The spatial and temporal distribution of programmed cell death (PCD) during petal senescence of Osmanthus fragrans

Zou, J., Cai, X., Wang, C.
Acta horticulturae 2017 no.1185 pp. 315-324
DNA fragmentation, Osmanthus fragrans, Western blotting, adenosine triphosphate, apoptosis, complementary DNA, corolla, cytochrome c, cytosol, economic valuation, ethylene, genes, genetic markers, lipid peroxidation, longevity, models, proteinases, quantitative polymerase chain reaction, reactive oxygen species, shrinkage, woody plants, China
Sweet osmanthus (Osmanthus fragrans Lour.), one of the top ten traditional flowers in China, is an important ornamental and economical woody plant that has been commercially cultivated in China for over 2500 years due to its unique fragrance and medicinal properties. However, the lifespan of Osmanthus flowers is generally short, limiting both the ornamental and economic value. Petal senescence is considered a consequence of programmed cell death (PCD). It provides a model system to study the phenomenon and mechanisms of the flower senescence. In this study, physiological, cytological, and molecular markers were used to discuss the spatial distribution of PCD across the petal development and senescence of O. fragrans 'Liuye Jingui'. The release of cytochrome c (cyt c) into cytosol by western blotting analysis showed that it was clearly detected at stage 1 (0-day-old petals) and became prominent in the following two stages. Adenosine triphosphate (ATP) levels were found to be rapidly depleted throughout petal development. We also isolated the homolog of the defender against apoptotic death (DAD1) gene from Osmanthus petals (OsDAD1), and expression of OsDAD1 partial cDNA was dramatically down-regulated between stage 1 and stage 2 (1-day-old petals) by real-time PCR analysis, considerably before the first visible senescence symptom. Together with the data from our previous work, it is concluded that the cyt c release, DAD1 reduction, and ATP depletion are very early events in the PCD triggering process. Both ethylene and proteases are executors of PCD and play important regulatory roles in petal senescence of Osmanthus flowers. Nuclear shrinkage, DNA fragmentation, reactive oxygen species (ROS) generation, and lipid peroxidation were late events of PCD, which occurred more rapidly at the last two stages by the time of visible senescence symptoms. This work offers a new theoretical basis for delaying the senescence of woody flowers and provides an academic and practical basis for selecting long-blooming O. fragrans.