Salsola arbusculiformis, a C-3-C-4 intermediate in Salsoleae (Chenopodiaceae)

Salsola arbusculiformis is identified as a C-3-C-4 intermediate species bas ed on anatomical, biochemical and physiological characteristics. This is th e first report of a naturally occurring intermediate species in the Chenopo diaceae, the family with the largest number of C-4 species amongst the dico ts. In the genus Salsola, most species have Salsoloid anatomy with Kranz ty pe bundle sheath cells and C-4 photosynthesis, while a few species have Sym pegmoid anatomy and were found to have non-Kranz type bundle sheath cells a nd C-3 photosynthesis. In the cylindrical leaves of C-4 Salsola with Salsol oid type anatomy, there is a continuous layer of distinct, chlorenchymatous Kranz type bundle sheath cells surrounded by a single layer of mesophyll c ells; whereas species with Sympegmoid type anatomy have an indistinct bundl e sheath with few chloroplasts and multiple layers of chlorenchymatous meso phyll cells. However, S. arbusculiformis has intermediate anatomical featur es. While it has two-to-three layers of mesophyll cells, characteristic of Sympegmoid anatomy, it has distinctive, Kranz-like bundle sheath cells with numerous chloroplasts and mitochondria. Measurements of its CO2 compensati on point and CO2 response of photosynthesis show S. arbusculiformis functio ns as an intermediate species with reduced levels of photorespiration. The primary means of reducing photo respiration is suggested to be by refixing photorespired CO2 in bundle sheath cells, since analysis of photosynthetic enzymes (activity and immunolocalization) and (CO2)-C-14 labelling of initi al fixation products suggests minimal operation of a C-4 cycle. (C) 2001 An nals of Botany Company.