Salsola laricifolia, another C3-C4 intermediate species in tribe Salsoleae s.l. (Chenopodiaceae)

This study identifies Salsola laricifolia as a C-3-C-4 intermediate in tribe Salsoleae s. l., Chenopodiaceae, and compares S. laricifolia with the previously described C-3-C-4 intermediates in Salsoleae. Photosynthetic pathway characteristics were studied in four species of this tribe including S. laricifolia, C-3 Sympegma regelii, C-3-C-4 S. arbusculiformis, and C-4 S. arbuscula, using the approaches of leaf anatomy and ultrastructure, activities of ribulose 1-5-bisphosphate carboxylase/oxygenase (Rubisco) and PEP carboxylase (PEPC), CO2 compensation point, and immunolocalization of Rubisco, PEPC, and the P-subunit of glycine decarboxylase (GDC). Salsola laricifolia has intermediate features, with near continuous and distinctive Kranz-like cells (KLCs) compared with the C-3-Sympegmoid anatomical type and the C-3-C-4 intermediate S. arbusculiformis, a relatively low CO2 compensation point (30.4 lmol mol(-1)) and mesophyll (M)-to KLC tissue ratio, mitochondria in KLCs primarily occurring along the centripetal wall, and specific localization of P-protein GDC in the KLCs. The C-3-type isotope value (-22.4 %), the absence of the clear labeling for PEPC in M cells, and the low activity of the PEPC enzyme (61.5 lmol mg(-1) chlorophyll -1 h -1) support the identification of S. laricifolia as a type I C-3-C-4 intermediate. Although these C-3-C-4 intermediate species have different structural features, one with discontinuous KL cells and the other with continuous, they have similar characteristics in physiology and biochemistry.