Structural changes in secretory canals associated with fruit development in Ajowan (Trachyspermum ammi Sprague)

Abstract

Ajowan (Trachyspermum ammi Sprague) fruits (Apiaceae) accumulate essential oil in compartments referred to as canals (vittae). T.ammi is one of the most important herbs used in Ayurveda (1). Iranian traditional herbal medicine recommends the use of Ajowan fruits also as digestive stimulant. A high proportion of thymol has been selectively demonstrated by Magnetic Resonance Imaging in the essential oil of mature Ajowan fruits (2). It has also been reported that different harvest stages affect the number of oil components in Ajowan fruits (3). The present research has focused on the relationship between the secretion process and reproductive development in T.ammi. Flowers and fruits were collected from wild growing plants at 6 ontogenic stages. Samples were fixed with glutaraldehyde and osmium tetroxide, dehydrated in acetone and embedded in resin. Semithin sections were stained with toluidine blue. Six canals were distinguishable in the ovary wall of the partly open flowers. A single layer of orderly arranged cells reperesented the schizogenous cavity. The cytoplasm of these cells increased in density, and reached the highest level in flowers at full bloom. The immature fruit exhibited the features of the most active secretory phase, i.e., higher amount of the secreted material lining the cavity and maximum width of the canal. The cells underwent post-secretory phase throughout the fruit maturation. They were compressed, with a degenerative protoplasm in dry mature pericarp. Results of the present histological study confirm previous analytical data (3) and recommend the use of immature stage for the best efficiency of Ajowan.