Structure and distribution of glandular and non-glandular trichomes on above-ground organs in Inula helenium L. (Asteraceae)

Aneta Sulborska

doi:10.5586/aa.2013.048

Abstract

Micromorphology and distribution of glandular and non-glandular trichomes on the above-ground organs of <em>Inula helenium </em>L. were investigated using light and scanning electron microscopy (SEM). Two types of biseriate glandular trichomes, i.e. sessile and stalk hairs, and non-glandular trichomes were recorded. Sessile glandular trichomes were found on all examined <em>I. helenium </em>organs (with their highest density on the abaxial surface of leaves and disk florets, and on stems), whereas stalk glandular trichomes were found on leaves and stems. Sessile trichomes were characterised by a slightly lower height (58–103 μm) and width (32–35 μm) than the stalk trichomes (62–111 μm x 31–36 μm). Glandular hairs were composed of 5–7 (sessile trichomes) or 6–9 (stalk trichomes) cell tiers. Apical trichome cell tiers exhibited features of secretory cells. Secretion was accumulated in subcuticular space, which expanded and ruptured at the top, and released its content. Histochemical assays showed the presence of lipids and polyphenols, whereas no starch was detected. Non-glandular trichomes were seen on involucral bracts, leaves and stems (more frequently on involucral bracts). Their structure comprised 2–9 cells; basal cells (1–6) were smaller and linearly arranged, while apical cells had a prozenchymatous shape. The apical cell was the longest and sharply pointed. Applied histochemical tests revealed orange-red (presence of lipids) and brow colour (presence of polyphenols) in the apical cells of the trichomes. This may suggest that beside their protective role, the trichomes may participate in secretion of secondary metabolites.

Highlights

Inula helenium is a large perennial growing in North America, Europe, Asia Minor, and Japan
Location of glandular and mechanical trichomes was identified and morphometric and structural analyses were performed
Sessile trichomes were more abundant and they were found on the leaves (Figs 2 A; 3 B, D; 4 A, D, E), primarily on the abaxial epidermis, stems (Figs 2 H; 3 A, C, E–G), involucral bracts (Fig. 4 C), ray-floret corolla (Fig. 3 H) and in the apical teeth of the disk-floret corolla

Summary

Introduction

Inula helenium is a large (up to 2 m high) perennial growing in North America, Europe, Asia Minor, and Japan. Likewise in many other representatives of Asteraceae [3,4,5], the above-ground organs of the species bear glandular and non-glandular trichomes. Substances produced by glandular trichomes may function as repellents against herbivores and pathogens [6,7,8], limit the transpiration rate, and reduce leaf temperature [9]. Withering and falling leaves with intact glandular hairs may provide a phytotoxic environment for germinating seeds and growing seedlings [6]. Non-glandular trichomes often act as a physiological barrier against herbivores and contribute to plant adaptation to environmental conditions, in dry environments [10,11]

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