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The drought-tolerant plant Caragana korshinskii Kom· was used to investigate the relative contribution of photorespiration and antioxidative mechanisms to water-stress adaptations across the Loess Plateau. The samples were collected from Shenmu, Yulin and Dongsheng along with the reduction of rainfall. The results showed the lower leaf water potential and the lower content of O2 - and malondialdehyde (MDA) were found in the plants in drier zone· H2O2 didn't show a significant difference among these sampling sites. Both photorespiratory rate (PR) and net photosynthetic rate (PN) increased with the decrease of rainfall. Low rainfall upregulated the gene expression and activities of photorespiratory enzymes. In addition, ascorbate peroxidase (APX), glutathione peroxidase (GPX) and superoxide dismutase (SOD) activity and reduced glutathione (GSH), ascorbic acid (AsA) contents increased with the decrease of rainfall, whereas catalase (CAT) activity decreased. These results indicate photorespiration could play a protective role for the photosynthetic apparatus from photoinhibition and photodamage under low rainfall levels, which could also act together with the antioxidation system to improve the tolerance to drought in C. korshinskii. [ABSTRACT FROM AUTHOR]

C4 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 C4 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 C4 species has been identified, Cleome gynandra L. There is recent interest in selecting and developing a C4 species from the family Cleomaceae as a model C4 system, since it is the most closely related to Arabidopsis, a C3 model system (Brown et al. 2005). From screening more than 230 samples of Cleomaceae species, based on a measure of the carbon isotope composition (?13C) in leaves, we have identified two additional C4 species, C. angustifolia Forssk. (Africa) and C. oxalidea F.Muell. (Australia). Several other species have ?13C values around ?17? to ?19?, suggesting they are C4-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 C4 species, C. paradoxa R.Br., a C3?C4 intermediate species, and 6 others which were characterised as C3 species. Cleome gynandra has C4 features based on low CO2 compensation point (?), C4 type ?13C values, Kranz-type leaf anatomy and bundle sheath (BS) ultrastructure, presence of C4 pathway enzymes, and selective immunolocalisation of Rubisco and phosphoenolpyruvate carboxylase. Cleome paradoxa was identified as a C3?C4 intermediate based on its intermediate ? (27.5?molmol?1), ultrastructural features and selective localisation of glycine decarboxylase of the photorespiratory pathway in mitochondria of BS cells. The other six species are C3 plants based on ?, ?13C values, non-Kranz leaf anatomy, and levels of C4 pathway enzymes (very low or absent) typical of C3 plants. The results indicate that this is an interesting family for studying the genetic basis for C4 photosynthesis and its evolution from C3 species. [ABSTRACT FROM AUTHOR]