Distribution of Glandular Trichome and Correlation with Volatile Compounds in Phalaenopsis Floral Organs

Phalaenopsis is the most commercialized ornamental orchid plant globally, with floral fragrance being one of its core ornamental traits. Glandular trichomes are key physiological structures for the synthesis and release of fragrant compounds. At present, the mechanism of floral fragrance synthesis in Phalaenopsis has been preliminarily explored, but the distribution of glandular trichomes and its association with volatile components are still unclear.

The objective of this study is to clarify the physiological structural basis of fragrance release in Phalaenopsis, analyze the correlation between glandular trichome distribution and volatile components, and to provide theoretical support for understanding fragrance release mechanisms and fragrant varieties breeding.

The strongly fragrant ‘Frigdaas Huang Chan’, moderately fragrant ‘Brother Sara Gold’, lightly fragrant ‘Frigdaas Hongyi’, and non-fragrant ‘Frigdaas Peach’ were used as experimental materials. Neutral red staining, scanning electron microscopy, histochemical staining and headspace-solid phase microextraction-gas chromatography-mass spectrometry (HS-SPME-GC-MS) were used to systematically analyze the glandular trichome morphology, distribution, cellular reserve accumulation characteristics, and differences in volatile components. Correlation analysis was conducted to clarify the relationships between glandular trichome density and volatile content, as well as odor activity values (OAVs).

Glandular trichomes in Phalaenopsis were primarily distributed on the adaxial side of sepals and petals, predominantly as capitate trichomes, with minimal distribution on the abaxial side. Higher fragrance intensity was associated with greater glandular trichome density, following the order: strongly fragrant＞moderately fragrant＞lightly fragrant＞non-fragrant. Floral organs of fragrant varieties accumulated both starch and lipids, while the non-fragrant ‘Frigdaas Peach’ accumulated only starch. The extent of lipid accumulation was closely related to fragrance intensity. Sepals were identified as the main sites of fragrance release, with representative volatile compounds including linalool, eucalyptol, myrcene, and α-pinene. The density of glandular trichomes on the adaxial side of the dorsal and lateral sepals showed a highly significant positive correlation (P＜0.01) with both total volatile compound contents and total OAVs.

Glandular trichomes in Phalaenopsis floral organs are predominantly located on the adaxial side of sepals and are mainly capitate in type. The distribution density is positively correlated with the content of representative volatile compounds and OAVs. Additionally, lipid accumulation in floral organ cells is a significant material characteristic of fragrant Phalaenopsis varieties. This study clarifies the structural and material basis of fragrance release in Phalaenopsis, which can provide a basis for understanding the mechanisms of floral fragrance release and the selection and breeding of fragrant varieties.