Intraspecifíc variability in Alloteropsis semialata (R. Br.) Hitchc.

Abstract

Intraspecific variability in Alloteropsis semialata (R. Br.) Hitchc. is shown ultrastructurally with particular regard to the structure of the bundle sheath and the development of the dimorphic chloroplasts in both the C₃ and C₄ forms of this species.

A. semialata is known to possess two distinct anatomical forms — Kranz and non-Kranz — within one species and occurring within a single ecological niche. Kranz and non-Kranz anatomy is known to be correlated with C₃ and C₄ physiology respectively.

Transverse sections of leaf portions taken at midsheath, at the ligule and at midlamina show plastids with different morphologies at different ontogenetic stages. Plastid form is related to the stage of development, the influence of light on the emerging leaf and the C₃ or C₄

form of A. semialata. Stages from amyloplast to chloroplast are investigated with regard to fine structure. Leaf transverse sections are examined microscopically and formation of new bundles, chiefly in the lamina is traced. Differences in anatomy and distribution of vascular bundles are more evident in the lamina than in the colourless leaf sheath.

Both C₃ and C₄ forms of A. semialata are found to show chloroplast dimorphism in vascular bundle sheath and mesophyll cells. This is shown to differ in the two forms. The specialized chloroplasts of the Kranz sheath are shown to develop in the inner or mestome sheath, and not in the parenchyma sheath as in some other members of the Kranz Panicoideae.

Features of A. semialata,  such as the double bundle sheath, granal chloroplasts and large numbers of mitochondria in bundle sheath cells, in the C₄ form, question the current classification of this grass as a malate former.