Structure and enzyme expression in photosynthetic organs of the atypical C4 grass Arundinella hirta

Abstract

In its leaf blade, Arundinella hirta has unusual Kranz cells that lie distant from the veins (distinctive cells; DCs), in addition to the usual Kranz units composed of concentric layers of mesophyll cells (MCs) and bundle sheath cells (BSCs; usual Kranz cells) surrounding the veins. We examined whether chlorophyllous organs other than leaf blades-namely, the leaf sheath, stem, scale leaf, and constituents of the spike-also have this unique anatomy and the C 4 pattern of expression of photosynthetic enzymes. All the organs developed DCs to varying degrees, as well as BSCs. The stem, rachilla, and pedicel had C 4 -type anatomy with frequent occurrence of DCs, as in the leaf blade. The leaf sheath, glume, and scale leaf had a modified C 4 anatomy with MCs more than two cells distant from the Kranz cells; DCs were relatively rare. An immunocytochemical study of C 3 and C 4 enzymes revealed that all the organs exhibited essentially the same C 4 pattern of expression as in the leaf blade. In the scale leaf, however, intense expression of ribulose-1,5-bisphosphate carboxylase/ oxygenase (Rubisco) occurred in the MCs as well as in the BSCs and DCs. In the leaf sheath, the distant MCs also expressed Rubisco. In Arundinella hirta, it seems that the ratio of MC to Kranz cell volumes, and the distance from the Kranz cells, but not from the veins, affects the cellular expression of photosynthetic enzymes. We suggest that the main role of DCs is to keep a constant quantitative balance between the MCs and Kranz cells, which is a prerequisite for effective C 4 pathway operation.

C4 Cycles: Past, Present, and Future Research on C4 Photosynthesis

“…One notable exception to this repeating pattern is found in Arundinella hirta, a C 4 grass that exhibits an atypical anatomy where wreaths of so-called distinctive (D) cells are found between V-BS-M-M-BS-V units (Crookston and Moss, 1973;Dengler and Dengler, 1990). The D cells carry out the same function as BS cells but are not themselves associated with veins (Reger and Yates, 1979;Dengler et al, 1996;Wakayama et al, 2006). Notably, if the number of BS and D cells is combined, the 1:1 ratio is also observed in A. hirta.…”

Chapter 4 C4 Photosynthesis: Kranz Forms and Single-Cell C4 in Terrestrial Plants

“…Structural and biochemical forms of Kranz anatomy in relation to the number of independent C 4 lineages in family Poaceae. Distinctive cells have structural and biochemical characteristics similar to the BS cells (Crookston and Moss, 1973;Dengler et al, , 1996Wakayama et al, 2002Wakayama et al, , 2003Wakayama et al, , 2006. 1.…”

Inheritance of C3―C4Intermediate Photosynthesis in Reciprocal Hybrids BetweenMoricandia Arvensis(C3―C4) andBrassica Oleracea(C3) That Differ in Their Genome Constitution

“…However, t h e m o l e c u l a r m e c h a n i s m t h a t r e g u l a t e s t h e intercellular expression of the GDC P-protein has not yet been identified (Thole and Rawsthorne, 2003). In the future, the molecular and genetic mechanisms responsible for directing structural differentiation such as the specialized BS cells and dense leaf vasculature found in the leaves of C 3 -C 4 intermediate and C 4 plants should also be elucidated (Ueno, 2001;Surridge, 2002;Brown et al, 2005;Ueno et al, 2006a;Wakayama et al, 2006).…”