Early Leaf Ontogeny and Shoot Development in Brownea Ariza (Leguminosae)

Abstract

Brownea ariza Benth. (Leguminosae: Caesalpinioideae) shows early shoot tip abortion and subsequent renewal growth from the pseudoterminal bud. This species is unusual in that the entire shoot system is formed before flushing from the bud occurs, shoot tip abortion occurs during flushing, and the aborting portion contains three to six leaves as well as primordial structures varying from hood to peg shape. This study focused on the morphological changes from initiation of scale and foliage leaf primordia in the "resting" renewal bud through bud elongation to flushing and bud abortion. Scanning electron microscopy revealed that embryonic scale leaves are hood-shaped while foliage leaf primordia show early segmentation into leaflets and stipules. No transitional stages were observed. Bud scales and foliage leaves show opposite developmental trends. In bud scales, length at maturity increases from first to last formed, while length decreases in sequentially formed foliage leaves. Early in leaf development the stipules keep pace with the elongation of the rachis. When the bud reaches about one half of its final length the leaf rachis begins to exceed the lengths of its stipules. This young rachis terminates in a distinct mucro that persists until maturity at which time it abscises. Growth patterns indicate that mucro and rachis are a single developmental unit. The early abortion of a shoot tip containing several leaves cannot be easily rationalized. Previous suggestions have involved maintenance of form and ecological adaptation. We add the possibility of elimination of cell progeny encumbered by mutations. From this and other studies of this group, it is clear that at maturity leaves of different species may look alike, e.g., Hymenaea and Colophospermum are bifoliolate; Brownea, Saraca, and others are multifoliolate. However, early stages of leaf ontogeny are quite diverse and may be of systematic value, since these early differences are lost or masked by later development.

Comparative leaf development of juvenile and adult Pseudopanax crassifolius

“…Acropetal initiation of the lamina was observed by Avery (1933) and Cross (1937) and may be a common feature of simple leaf development. The initiation of leaflets in compound leaves and lobes in simple leaves has been observed to occur in both acropetal (Kaplan 1980;Gould et al 1986;Merrill 1979Merrill , 1986Dengler 1984;Stein and Johnson 1990) and basipetal (Troll 1939;Snow and Snow 1941) (Fig. 39), median (Fig.…”