Wisteria, a genus of flowering plants in the Fabaceae family, includes 10 species of deciduous woody vines. Wisteria sinenesis and W. floribunda, two species native to East Asia, were introduced to North America in the 1800s. Because of their spectacular racemes in the spring, ease of establishment, hardiness, fast growth, and long lifespan, chinese wisteria and japanese wisteria have become two of the most popular flowering vines in the United States since their introduction. However, these same characters that have made chinese and japanese wisterias popular ornamental plants have also contributed to their aggressiveness. The vines of chinese and japanese wisterias easily overtake native shrubs and trees through shading and strangling. In the southeastern United States, chinese and japanese wisterias have been listed as invasive weeds (Trusty et al., 2007a). Although these plants can be controlled by manual removal or herbicides, their management in the wild can be very challenging.
To establish successful control program for these exotic wisterias, it will be important to understand the biology of these plants, especially their reproductive biology. Chinese and japanese wisterias are known for their fragrant flowers, a trait of important aesthetic value. The strong floral scent of wisterias may also be important for their reproduction. For many plants, floral scent plays a critical role in attracting pollinators for pollination (Wright and Schiestl, 2009). Wisteria flowers have been observed to be visited by bees, flies, and hummingbirds. Characterizing the volatile chemistry of wisteria flowers will be important for us to understand the role of floral scent of these species for their reproductive success, which may lead to new strategies for the control of these plants as exotic weeds. To this end, the first objective of this study was to identify the volatile compounds emitted from the flowers of chinese wisteria and japanese wisteria.
The composition and amounts of floral volatiles may change during anthesis. Such changes can be regulated by various internal and external factors, including light, flowering stages, diurnal pattern, and visitation by pollinators (Andrews et al., 2007). It is advantageous for the plants to have their scent output at maximal levels only when their potential pollinators are active so as to conserve energy (Dudareva and Pichersky, 2000). The rhythmic pattern of floral volatile emission has been demonstrated in many herbaceous species (Altenburger and Matile, 1988; Jiang et al., 2011; Lee et al., 2010). Its occurrence in woody species is much less studied. Therefore, the second objective of this study was to determine whether the emission of floral volatiles from wisteria displays a diurnal pattern and, if so, whether the diurnal pattern is regulated by light, circadian clock, or both.
The emission of plant volatiles may be regulated by plant hormones and signaling molecules. For example, ethylene, a hormone important for many aspects of plant biology, including flower development and senescence, has been shown to be involved in the regulation of floral volatile emissions in certain plant species (Jiang et al., 2011; Underwood et al., 2005). The jasmonic acid (JA) pathway was reported to regulate production and emission of volatiles from vegetative tissues for plant defense (Howe, 2004). In addition, salicylic acid (SA) also is involved in the production and release of some defense volatile compounds (Zhao et al., 2010). However, little is known about whether the JA and SA signaling pathways play a role in regulating the production and emission of floral volatiles, especially in woody plants. Thus, the third objective of this study was to determine whether silver thiosulphate [STS (an ethylene inhibitor)], JA, and SA can affect the emission of volatiles from wisteria flowers.
In this article, we report the comprehensive analysis of wisteria floral scent: chemical composition, emission patterns, and regulation. Volatile chemicals emitted from the flowers of chinese wisteria and japanese wisteria were collected using a dynamic headspace technique and identified using gas chromatography–mass spectrometry (GC-MS). Then chinese wisteria was used as a model for further analysis of emission dynamics and regulation of floral volatiles. The significance of floral scent to the reproductive biology of chinese and japanese wisterias is discussed.
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