Ontogeny, histochemistry, and structure of the glandular trichomes in Bignonia aequinoctialis (Bignoniaceae)

Abstract

Ontogeny, histochemistry, and structure of glandular trichomes in Bignonia aequinoctialis (Bignoniaceae). Glandular trichomes commonly occur in Bignonieae; however, because ontogenetic studies are scarce much still needs to be learned and understood about the function of these secretory structures in the species of the tribe. Therefore, the present study aimed to investigate not only the secretion and function of the glandular trichomes of B. aequinoctialis but also their occurrence and development. Samples of leaflets, prophylls of the axillary buds, floral calyx in anthesis, and flower buds in different stages of development were collected, fixed, and processed according to the usual methods for light microscopy and scanning electron microscopy. Diverse ants were found in all the plants; ants located near to the trichomes were collected. B. aequinoctialis has two types of glandular trichomes on the aerial vegetative axis and the reproductive axis: patelliform and peltate. Both are distributed in large quantities in the early stages of the plant’s development, exhibit asynchronous development, and have protodermic origin. The peltate glandular trichome consists of a peduncle cell and several cells in the head, which characterize the head as a multicellular secretory portion in disk shape. The patelliform glandular trichome is formed by one large peduncle cell and a secretory epidermis uniseriate, in columnar form. Histochemical tests identified a sugary secretion from the patelliform glandular trichomes, which serves as the ants’ reward. Thus, these glandular trichomes have been shown to have an important role in the insect–plant mutualistic relationship.