Transition from C to proto-Kranz to C-C intermediate type in the genus Chenopodium (Chenopodiaceae).

The Chenopodiaceae is one of the families including C species among eudicots. In this family, the genus Chenopodium is considered to include only C species. However, we report here a transition from C photosynthesis to proto-Kranz to C-C intermediate type in Chenopodium. We investigated leaf anatomical and photosynthetic traits of 15 species, of which 8 species showed non-Kranz anatomy and a CO compensation point (Γ) typical of C plants. However, 5 species showed proto-Kranz anatomy and a C-like Γ, whereas C. strictum showed leaf anatomy and a Γ typical of C-C intermediates. Chenopodium album accessions examined included both proto-Kranz and C-C intermediate types, depending on locality. Glycine decarboxylase, a key photorespiratory enzyme that is involved in the decarboxylation of glycine, was located predominantly in the mesophyll (M) cells of C species, in both M and bundle-sheath (BS) cells in proto-Kranz species, and exclusively in BS cells in C-C intermediate species. The M/BS tissue area ratio, number of chloroplasts and mitochondria per BS cell, distribution of these organelles to the centripetal region of BS cells, the degree of inner positioning (vacuolar side of chloroplasts) of mitochondria in M cells, and the size of BS mitochondria also changed with the change in glycine decarboxylase localization. All Chenopodium species examined were C-like regarding activities and amounts of C and C photosynthetic enzymes and δC values, suggesting that these species perform photosynthesis without contribution of the C cycle. This study demonstrates that Chenopodium is not a C genus and is valuable for studying evolution of C-C intermediates.