More than Scales: Evidence for the Production and Exudation of Mucilage by the Peltate Trichomes of Tillandsia cyanea (Bromeliaceae: Tillandsioideae).

Igor Ballego-Campos,Rafaela C Forzza,Elder A S Paiva

doi:10.3390/plants9060763

Abstract

Bromeliad scales have been investigated extensively due to their recognition as a key ecological and evolutionary feature of Bromeliaceae. However, much remains unknown about such trichomes and only recently mucilage exudation was described for them in a species of the subfamily Bromelioideae. The present study aimed to investigate the secretion present in inflorescences of Tillandsia cyanea Linden ex K. Koch (Tillandsioideae) to determine whether the scales of this species also produce and release secretions. Samples of young and mature portions of inflorescences were collected and prepared according to standard methods for light and electron microscopy. Anatomical and ultrastructural results indicate that the secretion is produced by the wing portion of typical peltate trichomes on the adaxial surface of bracts. The secretory activity begins in the early stages of trichome expansion and characteristically occurs in cells exhibiting a porous cuticle and dense cytoplasm with numerous mitochondria and dictyosomes. Histochemical tests confirmed mucilage secretion and revealed proteins in the exudate. These data comprise the first record of mucilage exudation by trichomes within Tillandsioideae and indicate that this capacity may be more relevant to bromeliad biology than previously considered. Functional aspects and colleter-like activity are also discussed.

Highlights

The structure and function of the typical bromeliad indumentum have been studied for more than a century [1,2,3,4,5,6,7,8,9,10], and much work is still being performed in this regard [11,12,13,14,15,16]
As far as we know, this is the first record for glandular activity by trichomes within Tillandsioideae associated with the release of a mucilaginous exudate
Such an account confirms that the secretory capacity of scales in bromeliad inflorescences is more common than previously considered and may constitute a feature with relevant ecological and evolutionary implications for Bromeliaceae

Summary

Introduction

The structure and function of the typical bromeliad indumentum have been studied for more than a century [1,2,3,4,5,6,7,8,9,10], and much work is still being performed in this regard [11,12,13,14,15,16]. Amongst the eight subfamilies currently accepted for Bromeliaceae, Tillandsioideae is the most diverse with about 1486 species [25,26,27,28] It is understandable, that trichomes in this subfamily have been extensively described in the literature, mainly due to their remarkably organized and complex structure, which is often associated with water and nutrient absorption capacity [2,7,8,9,15,18,21,29].

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Results

Discussion

Conclusion