The Development, Structure and Function of Dendroid Colleters in Psychotria kirkii Hiern (Rubiaceae)

Publisher Website
Google Scholar
Abstract
The dendroid colleters of the leaf nodulated Rubiaceous shrub Psychotria kirkii Hiern. have been studied with respect to their development, structure and function. The colleters, which arise from the adaxial surface of stipules of apical and lateral shoots, secrete a protein/carbohydrate mucilaginous substance in which is maintained a colony of leaf nodule bacteria. The colleters are multicellular and multiseriate, consisting of a two to four cell thick stalk from which radiate up to 70 elongate secretory branch cells. Cuticle envelops both stalk and branch cells in early developmental stages and as secretory activity increases this cuticle is largely lost in two different ways. The major part is forced off the branch cell surface through the passage of a largely carbohydrate component of the mucilage which surrounds the colleters: a second method of cuticle loss involves the passage from the cell of small electron-translucent bodies which become coated with cuticle as they exit the cell. The mucilage in which the bacterial cells are found provides a vehicle whereby the bacteria are able to enter the leaves, thus leading to the initiation of leaf nodules.