Senescence is an age-dependent deterioration process at the cellular, tissue, organ, or organism level, leading to death or the end of the lifespan (Noodén, 1988). The wilting of flower petals is a deliberate and precisely controlled senescence event in plants and has attracted many studies on flower senescence. Studies suggest that much of the biochemistry of the petal cells' disassembly is shared and quite similar to the events that have been demonstrated in leaves and other organs (Reid and Chen, 2007). Senescence of plant tissues is generally accompanied by respiration increases; breakdown of carbohydrates, proteins, lipids, and nucleic acids (Singh et al., 2000); higher production of reactive oxygen species (ROS) (Del Rio et al., 1998); increased contents of malondialdehyde (MDA) (Hodges et al., 1999); and gradual loss in the ability of scavenging enzymes to neutralize free radicals (Kanazawa et al., 2000). It is necessary to elucidate the physiological mechanisms underlying the changes and co-relationship of these factors to manipulate the flower senescence. To date, the importance of extending flower longevity to commercial floriculture has led to studies that have generated a wealth of information on physiological, biological, and molecular mechanisms of flower senescence in many floricultures such as petunia (Shibuya et al., 2004), rose (Kumar et al., 2008), and carnation (Wu et al., 1991).
Freesia is a kind of bulbous crops with high value for its colorful and aromatic flowers (Wang, 2007). Several studies on breeding, tissue culture, and postharvest biology of this crop had been performed (Qin and Lin, 1995; Wang, 2007). For instance, Spikman (1986, 1987, 1989) found that Freesia flowers were sensitive to ethylene. van Meeteren et al. (1995) reported the relationships between carbohydrate and vase life of Freesia flowers. Very little is known, however, about the respiration characteristics and the physiological metabolisms during their flower development and senescence. The aim of our present study was to comparatively characterize the respiratory and physiological changes during flower development and senescence in Freesia hybrid and to provide physiological basis for its postharvest handling.
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