Differentiation of cellular and biochemical features of the single‐cell C₄ syndrome during leaf development in Bienertia cycloptera (Chenopodiaceae)

Abstract

The terrestrial plant Bienertia cycloptera has been shown to accomplish C(4) photosynthesis within individual chlorenchyma cells by spatially separating the phases of carbon assimilation into distinct peripheral and central compartments. In this study, anatomical, physiological, and biochemical techniques were used to determine how this unique compartmentation develops. Western blots show ribulose-1,5-bisphosphate carboxylase (Rubisco) (chloroplastic) is present in the youngest leaves and increases during development, while levels of C(4) enzymes-pyruvate,Pi dikinase (chloroplastic), phosphoenolpyruvate carboxylase (PEPC) (cytosol), and NAD-malic enzyme (mitochondrial)-increase later in development. Immunolocalization confirmed this for Rubisco and PEPC. The youngest chlorenchyma cells have a central nucleus surrounded by monomorphic granal chloroplasts containing Rubisco. Later stages show progressive development of a central cytoplasmic compartment enriched with chloroplasts and mitochondria and of a peripheral cytoplasm with chloroplasts. A complex reticulum of connections between the compartments also developed and was characterized. δ(13)C isotope analyses show mature leaves have distinct C(4)-type isotope composition, while the composition in younger leaves is "C(4)-like." Based on the results, this form of single-cell C(4) photosynthesis develops from a common pool of organelles through partitioning to separate compartments, and the development of biochemically and ultrastructurally dimorphic chloroplasts.

Leaf Development in the Single-Cell C4 System in Bienertia sinuspersici: Expression of Genes and Peptide Levels for C4 Metabolism in Relation to Chlorenchyma Structure under Different Light Conditions

“…Leaves of B. sinuspersici (this work) and B. cycloptera (Voznesenskaya et al, 2005) have acropetal leaf development. There was a gradient of development and cellular differentiation from the base to the tip of the leaves, with the tip being at a more advanced stage than the base.…”

“…In chlorenchyma cells in the base of the young leaf, the nucleus is a dominant organelle in the cytoplasm, along with the surrounding chloroplasts, which occupy much of the cytoplasmic space (also, in B. cycloptera, the very youngest newly emerged leaves [less than 1 mm in length] are cytoplasmically dense and have little vacuole development [Voznesenskaya et al, 2005]). In B. sinuspersici, starch grains are present at this earliest stage in chlorenchyma cells; however, they have a scattered arrangement (Fig.…”

“…Nevertheless, three succulent species in family Chenopodiaceae, Bienertia cycloptera, Bienertia sinuspersici, and Suaeda aralocaspica (formerly classified as Borszczowia), were shown to have a unique mechanism of C 4 photosynthesis that occurs within individual photosynthetic cells (single-cell C 4 anatomy) by intracellular partitioning of enzymes and organelles (including dimorphic chloroplasts) into two compartments (Voznesenskaya et al, 2001(Voznesenskaya et al, , 2002Edwards et al, 2004;Akhani et al, 2005). S. aralocaspica has a single layer of elongated, cylindrical chlorenchyma cells in which functions of C 4 photosynthesis are spatially separated to opposite ends of the cells (Voznesenskaya et al, 2003).…”

“…The leaves of B. sinuspersici differ anatomically by having mostly one to two layers of chlorenchyma cells, in comparison with two to three layers in B. cycloptera. Furthermore, B. sinuspersici is distinguished from B. cycloptera by having longer cotyledon leaves and larger seeds, flowers, and chromosomes, together with a set of differences in micromorphological features (Akhani et al, 2005).…”

“…S. aralocaspica has a single layer of elongated, cylindrical chlorenchyma cells in which functions of C 4 photosynthesis are spatially separated to opposite ends of the cells (Voznesenskaya et al, 2003). B. cycloptera and B. sinuspersici have an unusual development of two cytoplasmic compartments in chlorenchyma cells, consisting of a large central cytoplasmic compartment (CCC) packed with chloroplasts and mitochondria and a peripheral layer of cytoplasm with chloroplasts (Voznesenskaya et al, 2002(Voznesenskaya et al, , 2005Akhani et al, 2005). The CCC, which is surrounded by the vacuole, is connected to the peripheral cytoplasm by cytoplasmic channels.…”