Poster: Photosynthesis

Abs # 345: Development of the single celled C₄ system in Borszczowia aralocaspica (Chenopodiaceae)

Presenter:	Edwards, Gerald E., edwardsg@wsu.edu
Authors	Edwards, Gerald E. (A)   Voznesenskaya, Elena V. (B)   Kiirats, Olavi  (A)   Artyusheva, Elena G. (C)   Franceschi, Vincent R. (A)
Affiliations:	(A): Washington State University (B): Komarov Botanical Institute, St. Petersburg, Russia (C): Urals State Economic University, Ekaterinburg, Russia
Web Site:	http://www.sci.wsu.edu/sbs/faculty.php3?pageID=6&id=28&groupID=1

The terrestrial plant Borszczowia aralocaspica has been shown to contain the C₄ photosynthesis mechanism within individual, structurally and biochemically polarized chlorenchyma cells rather than in a dual cell system, as has been the paradigm. Analysis of carbon isotope composition and ¹⁴CO₂ fixation shows that photosynthesis and growth occur through carbon acquired by C₄ photosynthesis. The development of this single cell C₄ system in chlorenchyma cells was studied by analysis of young, intermediate and mature leaves. The length of chlorenchyma cells doubles from young to intermediate, and from intermediate to the mature leaf stage. In young chlorenchyma, there is a single type of chloroplast, evenly distributed in the cytosol; all contain starch and Rubisco. During leaf development, the activities of Rubisco and especially PEPC and PPDK increase on a chlorophyll basis. As leaves mature, chloroplasts differentiate into two, distinct structural and biochemical types, spatially separated into the proximal and distal parts of the cell. The distal chloroplasts have reduced grana and little starch; those at the proximal ends have well developed grana and abundant starch. In mature leaves, pyruvate,Pi dikinase is expressed in chloroplasts at the distal end of the cells while Rubisco and ADPG pyrophosphorylase are selectively expressed in chloroplasts at the proximal end. Mitochondrial polarization occurs during development, as NAD-malic enzyme and glycine decarboxylase are expressed in mature but not young leaves and are localized in mitochondria at the proximal end of the cells. The data show that single cell C₄ develops from a single pool of identical organelles that develop differential biochemical functions and spatial partitioning in the cell during maturation.