Abstract
Opisthopappus taihangensis (Ling) Shih, a wild relative germplasm of chrysanthemum, releases a completely different fragrance from chrysanthemum species. We aimed to identify the volatile compounds of the leaves of O. taihangensis and four other Chrysanthemum species using headspace solid-phase micro-extraction combined with gas chromatography-mass spectrometry (HS-SPME-GC/MS). In total, 70 compounds were detected, and terpenoids accounted for the largest percentage in these five species. Many specific compounds were only emitted from O. taihangensis and not from the other four species. In particular, 1,8-cineole could be responsible for the special leaf fragrance of O. taihangensis as it accounted for the largest proportion of the compounds in O. taihangensis but a small or no proportion at all in other species. The glandular trichomes (GTs) in the leaves are the main organs responsible for the emission of volatiles. To explore the relationship between the emissions and the density of the GTs on the leaf epidermis, the shape and density of the GTs were observed and calculated, respectively. The results showed that the trichomes have two shapes in these leaves: T-shaped non-glandular trichomes and capitate trichomes. Histochemical staining analyses indicated that terpenoids are mainly emitted from capitate glandular trichomes. Correlation analysis showed that the volatile amount of terpenoids is highly related to the density of capitate trichomes. In O. taihangensis, the terpenoids content and density of capitate trichomes are the highest. We identified the diversity of leaf volatiles from O. taihangensis and four other Chrysanthemum species and found a possible relationship between the content of volatile compounds and the density of capitate trichomes, which explained the cause of the fragrance of O. taihangensis leaves.
Highlights
The aroma of plants is produced by a series of complex low-molecular-weight substances, which are a class of lipophilic substances with an aromatic odor [1]
Terpenoids accounted for the largest proportion in every species, ranging from 63.28% in C. lavandulifolium to 93.41% in O. taihangensis
Our research showed that terpenoids are the class of compounds that are mainly emitted by the leaves of the five wild species, and the amount of terpenoid emissions from the O. taihangensis leaves is the greatest
Summary
The aroma of plants is produced by a series of complex low-molecular-weight substances (typically less than 300 Da), which are a class of lipophilic substances with an aromatic odor [1]. In recent years with the continuous development of aromatic volatile compound extraction and detection technology, more than 2000 kinds of volatile organic compounds (VOCs) from 90 families, belonging to 991 species and subspecific taxa, have been identified [3]. These VOCs are classified into terpenoids, phenylpropanoids/benzenoids, and fatty acid derivatives according to their biosynthetic pathways [4,5]. The volatile compounds of chrysanthemum, such as Chrysanthemum. indicum var. aromaticum [9], cut chrysanthemum ‘Shen ma’ [10], and ‘gukhwa’ (C. morifolium), have recently been identified [11]
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