Panicum ecklonii, a new record of a C4 photosynthetic variant

Abstract

The anatomy of the leaf blade of P. ecklonii Nees collected in the eastern Cape was investigated with light and transmission electron microscopes. The leaf blades of this material contain three orders of closely spaced vascular bundles, each of which is surrounded by a radiating mesophyll, and an underlying bundle sheath, which consists of relatively thick-walled, chlorenchymatous cells. Bundle sheath cells contain large, centrifugally arranged, agranal chloroplasts. The longitudinal bundles are separated by one layer of achlorophyllous mesophyll. The outer tangential and radial walls of the bundle sheath cells contain a suberized compound middle lamella. Few mitochondria occur in bundle sheath cells and are usually closely associated with plasmodesmatal pits in the outer tangential walls of the bundle sheath cells. Large bundles are subtended by ad- as well as abaxial hypodermal sclerenchyma strands. Intermediate bundles are connected to the adaxial hypodermal sclerenchyma strands by a single-layered bundle sheath extension, and the bundle sheath is in direct contact with hypodermal sclerenchyma strands abaxially. Small bundles are embedded in mesophyll tissue. Specimens of P. ecklonii from the eastern Cape thus display typical C 4 NADP anatomy.