Mucilage secretion in the inflorescences of Aechmea blanchetiana: Evidence of new functions of scales in Bromeliaceae

The peltate trichomes of Bromeliaceae comprise an important feature of this plant group. Although recognized for their capacity for water and nutrient absorption, little is known concerning their secretory functions. This study aimed to identify and describe the structures observed to secrete mucilage in the inflorescences of Aechmea blanchetiana, a species of Bromeliaceae endemic to Brazil. Samples of different portions and developmental stages of inflorescences were collected and processed for study under light and electron microscopy. Mucilage is secreted by peltate trichomes covering the inflorescence axis, which have a structure typical of bromeliad scales, although often having an irregular shield commonly exhibiting a stellate outline. Secretion is performed by cells comprising the so-called wing portion of the trichome and begins even in initial stages of inflorescence expansion. In expanded portions, secretory activity ceases and the remaining secretion appears as a thin dehydrated film covering the inflorescence surface. Ultrastructural data show the presence of well-developed Golgi apparatus and endoplasmic reticulum, confirming a secretory function related to non-cellulosic polysaccharide production. We believe that the mucilage is related to protection against desiccation, especially at early stages of expansion. Such a functional role, in association with the nature and dynamics of the secretion, suggests that these structures act as colleters. As far as we know, this is the first record for exogenous secretory activity by the typical peltate trichomes of Bromeliaceae, and the first time when colleter-like functions have been considered and discussed in this family.