Physiological, anatomical and biochemical characterisation of photosynthetic types in genus Cleome (Cleomaceae)

C-4 photosynthesis has evolved many times in 18 different families of land plants with great variation in leaf anatomy, ranging from various forms of Kranz anatomy to C-4 photosynthesis occurring within a single type of photosynthetic cell. There has been little research on photosynthetic typing in the family Cleomaceae, in which only one C-4 species has been identified, Cleome gynandra L. There is recent interest in selecting and developing a C-4 species from the family Cleomaceae as a model C-4 system, since it is the most closely related to Arabidopsis, a C-3 model system ( Brown et al. 2005). From screening more than 230 samples of Cleomaceae species, based on a measure of the carbon isotope composition (delta C-13) in leaves, we have identified two additional C-4 species, C. angustifolia Forssk. (Africa) and C. oxalidea F.Muell. (Australia). Several other species have delta C-13 values around -17 parts per thousand to -19 parts per thousand, suggesting they are C-4-like or intermediate species. Eight species of Cleome were selected for physiological, anatomical and biochemical analyses. These included C. gynandra, a NAD-malic enzyme (NAD-ME) type C-4 species, C. paradoxa R.Br., a C-3-C-4 intermediate species, and 6 others which were characterised as C-3 species. Cleome gynandra has C (4) features based on low CO2 compensation point (Gamma), C-4 type delta C-13 values, Kranz-type leaf anatomy and bundle sheath (BS) ultrastructure, presence of C-4 pathway enzymes, and selective immunolocalisation of Rubisco and phosphoenolpyruvate carboxylase. Cleome paradoxa was identified as a C-3-C-4 intermediate based on its intermediate Gamma (27.5 mu mol mol(-1)), ultrastructural features and selective localisation of glycine decarboxylase of the photorespiratory pathway in mitochondria of BS cells. The other six species are C-3 plants based on Gamma, delta C-13 values, non-Kranz leaf anatomy, and levels of C-4 pathway enzymes (very low or absent) typical of C-3 plants. The results indicate that this is an interesting family for studying the genetic basis for C-4 photosynthesis and its evolution from C-3 species.