Transfer cells in trichomatous nectary in Adenocalymma magnificum (Bignoniaceae)

Transfer cells are specialized cells that play an important role where there are high energy costs due to facilitation of transmembrane flow of solutes. This study aimed to investigate the ontogenesis, histochemistry and ultrastructure of glandular trichomes focusing on stalk cells and their possible transfer function. Samples of prophylls of axillary buds, calyces of flowers in anthesis, and flower buds in different stages of development were collected, fixed and processed according to the common methods of microscopy. The glandular trichomes are composed of a secretory head with its cells in columnar format. The stalk is formed by two layers of cells, with the upper layer composed of cuboidal cells where the wall starts to thicken at the beginning of the pre-secretory phase. The secretion is heterogeneous, releasing glucose, other carbohydrates, lipids and phenolic compounds, with two types of release - eccrine and granulocrine. These trichomes are functionally termed as nectaries. The stalk cells appear as transfer cells since they have a thicker anticlinal wall with irregular ingrowths. The presence of transfer cells in the nectaries suggests a high specialization because it improves transport capacity of nectar and compensation in the high energy expenditure for its production and release.