Dedicated to Professor Han-Dong Sun on the occasion of his 70th birthday Plant trichomes (both glandular and nonglandular) are epidermal protuberances that have been found on the surfaces of aerial organs of most terrestrial plants, including angiosperms, gymnosperms, and bryophytes. [1] Glandular trichomes of plants often produce copious secondary metabolites with a wide range of structures and biological properties, including alkaloids, phenolics, and terpenoids. [2,3] These substances are secreted from glandular trichomes onto the plant surface or stored within the gland cavity, [1,2] and are often thought to serve as defenses against herbivores, but good evidence for their protective roles is usually lacking.
Among the plants of southwest China, Leucosceptrum canum Smith, a shrub or small tree belonging to the family Labiatae (= Lamiaceae), is densely covered with gray or yellowish trichomes. This species is perhaps the largest (up to 10 m high [4] ) and so far the only colored nectar plant [5] of all Labiatae species, and is found from the Himalayas to the southwest of China. [5,6] This plant is rarely attacked by herbivores and only occasionally by pathogens. We studied L. canum to identify the constituents of the glandular trichomes and investigate their possible function in plant defense.
Numerous gray or yellowish trichomes, both glandular and nonglandular, cover the buds, flowers, and especially the leaves of L. canum (Figure 1 A andB). Under the scanning electron microscope, the nonglandular trichomes appear as stellate structures, distributed on the stems, leaves (especially young leaves), buds, and bracts (Figure 1 C and D). The glandular trichomes include two main types: peltate and capitate trichomes. The peltate glandular trichomes have a
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