PARENT SESSION
Posters P8C C4 and CAM. Abstracts (685-698)

Leaf development of single cell C₄ plants of Bienertia (chenopodiaceae). Elena Voznesenskaya^*,1, Nuria Koteyeva¹, Simon Chuong², Vincent Franceschi², Hossein Akhani³, Gerald Edwards², ¹ Laboratory of Anatomy and Morphology, St. Petersburg, Russia² School of Biological Sciences, Pullman, WA, USA³ Department of Biology, Tehran, Iran

ABSTRACT- Bienertia cycloptera was recently shown to have a novel single cell C₄ photosynthetic mechanism (Voznesenskaya et al. 2002 Plant J). Mature chlorenchyma cells are differentiated into two cytoplasmic compartments, central and peripheral, differing in organelle structure and spatial compartmentation of key photosynthetic enzymes. The youngest leaves (0.5 mm long) have one layer of chlorenchyma cells and few chloroplasts, with a poorly developed thylakoid system. The starch granules are mostly located in the epidermis and water storage tissue, with little starch in chlorenchyma cells and labeling for Rubisco is very low. There is no labeling for the C₄ enzymes, PEPC and PPDK. At later stages, the chlorenchyma cells begin to differentiate very quickly, with intensive division of chloroplasts and mitochondria. The central cytoplasmic compartment (CCC), consisting of a ball of chloroplasts and mitochondria, begins to form around the nucleus, but it is still attached to cell walls along the periphery. In 2-3 mm leaves, labeling for Rubisco occurs in all chloroplasts of all tissues, while labeling for PEPC is low and mostly expressed in chlorenchyma cells, and there is no labeling for PPDK. Starch grains are still most obvious in water storage parenchyma, but also are prominent in chlorenchyma cells. In 5 mm leaves, the CCC is delineated and centered in the cell, and starch granules are obviously larger than in chloroplasts in the periphery. Rubisco is intensively labeled in the CCC chloroplasts, while labeling for PEPC occurs throughout the cytosol. Only in mature leaves (20-30 mm) is there complete differentiation of distinct chloroplasts and enzyme compartmentation, with Rubisco in the CCC and PPDK mostly in the peripheral chloroplasts. Analysis of compartmentation and quantities of photosynthetic enzymes, and carbon isotope composition during development, indicate that leaves initially express C₃-like photosynthesis and then undergo a developmental transition to C₄ photosynthesis.

KEY WORDS: development, ultrastructure, C₄ photosynthesis, immunolocalization