Development of biochemical specialization and organelle partitioning in the single‐cell C₄ system in leaves of Borszczowia aralocaspica (Chenopodiaceae)

Abstract

The terrestrial plant Borszczowia aralocaspica (Chenopodiaceae) has recently been shown to contain the entire C(4) photosynthesis mechanism within individual, structurally and biochemically polarized chlorenchyma cells rather than in a dual cell system, as has been the paradigm for this type of carbon fixation (Nature 414: 543-546, 2001). Analysis of carbon isotope composition and (14)CO(2) fixation shows that photosynthesis and growth of B. aralocaspica occurs through carbon acquired by C(4) photosynthesis. The development of this unique single-cell C(4) system in chlorenchyma cells was studied by analysis of young (0.2-0.3 cm length), intermediate (ca. 0.5-0.6 cm length), and mature leaves (ca. 3 cm length). The length of chlorenchyma cells approximately doubles from young to intermediate and again from intermediate to the mature leaf stage. In young chlorenchyma cells, there is a single type of chloroplast; the chloroplasts are evenly distributed throughout the cytosol, and all contain starch and rubisco. During leaf development, the activities of phosphoenolpyruvate carboxylase (PEPC; which is cytosolic), rubisco, and pyruvate,Pi dikinase (PPDK) increase on a chlorophyll basis. As leaves mature, chloroplasts differentiate into two distinct structural and biochemical types that are spatially separated into the proximal and distal parts of the cell (the proximal end being closest to the center of the leaf). The early stages of this polarization are observed in intermediate leaves, and the polarization is fully developed in mature leaves. The chloroplasts in the distal ends of the cell have reduced grana and little starch, while those at the proximal ends have well-developed grana and abundant starch. In mature leaves, PPDK is expressed in chloroplasts at the distal end of the cells, while rubisco and adenosine diphosphate glucose (ADPG) pyrophosphorylase are selectively expressed in chloroplasts at the proximal end of the cell. Mitochondrial polarization also occurs during development as nicotinamide-adenine dinucleotide phosphate-malic enzyme (NAD-ME) and the photorespiratory enzyme 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 C(4) develops from a single pool of identical organelles that develop differential biochemical functions and spatial partitioning in the cell during maturation.

The Cytoskeleton Maintains Organelle Partitioning Required for Single-Cell C4 Photosynthesis in Chenopodiaceae Species

“…Studies of this type on plants and macroalgae have dealt specifically with changes in chloroplast position in response to light intensity. The single-cell C 4 systems appear unique in that, early in leaf development, chloroplasts become separated into two cytoplasmic compartments and thereafter remain anchored (Voznesenskaya et al, 2003. This partitioning of chloroplasts in mature chlorenchyma cells does not change during the night or under different light conditions (E. Voznesenskaya, N. Koteyeva, S.D.X.…”

“…Seeds of Bienertia sinuspersici and Suaeda aralocaspica (formerly Borszczowia aralocaspica) (Schü tze et al, 2003;Voznesenskaya et al, 2003) were germinated on moist filter paper at room temperature. Seedlings were then transferred to 4-inch pots containing a soil mixture of 2 parts commercial potting soil, 1 part clay soil, 1 part sand, 0.5 parts Perlite, and 0.5 parts dolomite powder and were watered three times per week and once every week with MiracleGrow Excel 21-5-20 fertilizer and a salt solution (0.150 M NaCl).…”

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

“…1O). In previous studies, it has been shown among various C 4 species in family Chenopodiaceae that only Rubisco-containing chloroplasts tend to accumulate starch (Voznesenskaya et al, 1999(Voznesenskaya et al, , 2003(Voznesenskaya et al, , 2005. In leaves of both Kranz and singlecell C 4 species, starch accumulates in mature Rubiscocontaining chloroplasts and not in chloroplasts specialized to support the synthesis of C 4 acids by generating the substrate for PEPC.…”

“…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). 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).…”

Individual Maize Chromosomes in the C3 Plant Oat Can Increase Bundle Sheath Cell Size and Vein Density

“…As well as this diversity within the biochemistry of C 4 photosynthesis, there is also variation in terms of the leaf anatomy associated with the C 4 pathway. Although several examples of C 4 photosynthesis operating in single cells have been described (Reiskind et al, 1997;Casati et al, 2000;Reinfelder et al, 2000;Voznesenskaya et al, 2002Voznesenskaya et al, , 2003, most C 4 species compartmentalize carboxylation and decarboxylation activities into two distinct cell types. At least 22 variations of two-celled "Kranz" anatomy have been documented (Dengler and Nelson, 1999;Edwards and Voznesenskaya, 2011;Sage et al, 2012) whereby different cell types have been coopted as the photosynthetic carbon assimilation and photosynthetic carbon reduction tissue.…”