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

C 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 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 species has been identified, Cleome gynandra L. There is recent interest in selecting and developing a C species from the family Cleomaceae as a model C system, since it is the most closely related to Arabidopsis, a C model system (Brown et al. 2005). From screening more than 230 samples of Cleomaceae species, based on a measure of the carbon isotope composition (δC) in leaves, we have identified two additional C species, C. angustifolia Forssk. (Africa) and C. oxalidea F.Muell. (Australia). Several other species have δC values around -17‰ to -19‰, suggesting they are C-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 species, C. paradoxa R.Br., a C-C intermediate species, and 6 others which were characterised as C species. Cleome gynandra has C features based on low CO compensation point (Γ), C type δC values, Kranz-type leaf anatomy and bundle sheath (BS) ultrastructure, presence of C pathway enzymes, and selective immunolocalisation of Rubisco and phosphoenolpyruvate carboxylase. Cleome paradoxa was identified as a C-C intermediate based on its intermediate Γ (27.5 μmol mol), ultrastructural features and selective localisation of glycine decarboxylase of the photorespiratory pathway in mitochondria of BS cells. The other six species are C plants based on Γ, δC values, non-Kranz leaf anatomy, and levels of C pathway enzymes (very low or absent) typical of C plants. The results indicate that this is an interesting family for studying the genetic basis for C photosynthesis and its evolution from C species.