Photosynthetic Pathway-Related Ultrastructure of C₃, C₄ and C₃-Like C₃-C₄ Intermediate Sedges (Cyperaceae), With Special Reference to Eleocharis

Abstract

The ultrastructure of photosynthetic organs (leaf blades and culms) was investigated in eight species from four genera of sedges: Fimbristylis (C, fimbristyloid anatomy), Pycreus (C₄ chlorocyperoid anatomy), Rhynchospora (C₄ rhynchosporoid anatomy) - all NADP-ME (malic enzyme) type, and uninvestigated C₃, C₄ (eleocharoid anatomy, NAD-ME type) and C₃-like C₃-C₄ intermediate species of Eleocharis. Ultrastructural characteristics previously reported for the former anatomical types are largely confirmed, though some evidence of poorly developed peripheral reticulum in C₄ rhynchosporoid sedges is presented. Sedges, regardless of anatomical and biochemical type, possess a suberised lamella in photosynthetic organs which is invariably present in and confined to the mestome sheath cell walls, though it is often incomplete in the radial walls. By contrast with other C₄ sedges, NAD-ME Eleocharis species and the C₃-like C₃-C₄ intermediate E. pusilla possess abundant mitochondria and chloroplasts with well-stacked grana in the photosynthetic carbon reduction (PCR) (Kranz)/bundle sheath cells. Peripheral reticulum is well developed in NAD-ME species in both PCR and photosynthetic carbon assimilation (PCA) (C₄ mesophyll) chloroplasts, but differs from that seen in chlorocyperoid and fimbristyloid type sedges. The suberised lamella and starch grains (well preserved), and granal stacks (poorly preserved) are identifiable in dried herbarium material (Eleocharis). Prediction of C₄ biochemical type of sedges should be possible by combining anatomical, ultrastructural and δ¹³C value data. The significance of the ultrastructural similarities between the C₄ NAD-ME and C₃-C₄ intermediate Eleocharis species is discussed.