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KMID : 0381920060360010035
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Korean Journal of Microscopy
2006 Volume.36 No. 1 p.35 ~ p.45
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Structural Features of Various Trichomes in Vitex negundo during Development
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Lee Seung-Hee
Kim In-Sun
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Abstract
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Plants of Vitex negundo are known to develop numerous trichomes throughout their body, where certain trichome types have been believed to be one of the plausible structures for the unique scents. In the current study, structural aspects of the trichomes have been examined in leaves and stems of Vitex negundo using TEM and SEM. Trichome types as well as structural changes that occurred in certain trichomes during secretion have been mainly focused. Three types of glandular trichomes and two types of non-glandular trichomes were developed in the epidermis of young and mature Vitex negundo plants. The glandular trichomes included the peltate type (Type 1), the capitate type (Type 2), and degraded capitate type (Type 3), whereas the nonglandular warty trichomes contained the multicellular (Types 4) and unicellular type (Type 5). Type 1 and 2 consisted of head and stalk cells, but their number and size were different. One secretory cavity was formed from the four head cells in the former, but only two head cells were involved in the latter. The ytoplasmic density in the head cell was quite high and in particular, sER and Golgi bodies were well developed. At
initiation of their development, the cuticle layer of the head cells separated from the outer tangential wall to form a secretory cavity. Subsequently the cavity expanded acropetally and a large number of secretory vesicles continuously produced from the head cells until they filled the entire cavity. The cavity contained materials that would be soon discharged into intercellular spaces and/or into the air. The cavity began to decrease the volume by contracting at initial secretion but degrade rapidly within short time. It has been suggested that the mode of secretion in V. negundo is probably the eccrine secretion, since no break or rupture of the cavity has been observed during examination. Contrastingly Type 3 exhibited deterioration of the head cell at early stage. Type 4 was about 110~190 μm long, consisting of 2~3 cells, and distributed more in the adaxial epidermis compared to the abaxial surface. However, 20~30 μm long Type 5 was extremely dense in both epidermis. Among several trichome types, Type 1 and 2 probably play an important role in discharging unique aromatic scents in plants of V. negundo.
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KEYWORD
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Aromatic plant, Epidermis, Glandular trichome, Trichome type, Vitex negundo
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