| Caragana Fabr., belonging to the Papilionoideae (Leguminosae) and comprising about100species in the world, are mainly distributed in arid and semi-arid area of Asia and Europe. There are62species,9varieties and12geographic variants of this genus recorded in China. It mainly locates in the cold and drought areas in northwestern China. The species of Caragana play an important role in environmental protection, such as sand dune fixation and water conservation, in arid areas of China. They play important roles in ecological management and they have broad economic values. This paper presented the studies on the primary phylogenetic relationships of Caragana species and on the basis of results,6species represented different water resistance were chosen. The photosynthetic and ecophysiological traits with changes of some anti-oxidative physiological indices under a drying-rehydration cycle were studied. The main results were summarized as follows:1. Internal transcribed spacer (ITS) sequences of nuclear ribosomal DNA from29taxa of Caragana species and seven close relatives (all belong to Astralinae (Adens) Benth) were used for primary phylogenetic analysis. Length of the entire ITS region ranges from611to614bp in Caragana species sampled. The ITS-1region (229-231bp) was only slightly longer than ITS-2(216-220bp). No length variation was found in5.8S (163bp) region. The aligned sequences nrITS of Caragana are655bp, and170sites are variable, with107phylogenetically informative sites. The ITS sequences data are useful to resolve some relationships at lower taxonomic levels within Caragana. The species of Caragana we studied were distributed into five clades in general accordance with previous morphological and phytogeographical studies. The ITS data reveal that the species of Sect, tragacanthoides were dispersed in MP tree or ME tree. Although the morphology of C. ordosica is similar to C. tibetica, the nrITS results revealed an unexpectedly close relativeship between C. ordosica and C. roborovskyi. The ITS data also indicate C. davazamcii, C. korshinskii. C. intermedia, and C. microphylla are not the same species and Caragana Fabr. is not a monophyletic group with very close connection with Calophaca Fish. exDC. 2. To better understand the physiological characteristics in adapting to arid conditions employed by Caragana plants, the diurnal changes in photosynthetic traits and ecophysiological parameters in C. arborescens Lam.(mesophyte), C. microphylla Lam.(semiarid species), C. roborovskyi Kom., C. stenophylla Pojark., C. acanthophylla Pojark., and C. tragacanthoides Poir.(xerophytic species) were measured in Tenggeli desert. C. microphylla had the highest assimilation rate (A)(9.93±0.05μmolm-2s-1) in the morning but decreased over84%in the midday and resumed only54%in the afternoon. The four xerophytic species exhibited higher A, transpiration rate (E), stomatal conductance (gs), and lower water use efficient (WUE) than C. arborescens. In addition, the xerophytic species had more effective complex antioxidant systems. C. microphylla appears to increase drought and high temperature resistance by reducing stomata conductance and effectively osmotic adjustment, whereas the xerophytic species may use efficient antioxidative systems to adapt to the arid environment.3. To better understand the possible mechanisms employed by the xerophytic Caragana species against drought stress, the activities of antioxidant enzymes as well as the levels of their osmotically active solutes were studied in six Caragana species grown under a drying-rehydration cycle. Our data demonstrated that the guaiacol peroxidase (POD), superoxide dismutase (SOD) with the "ascorbate-glutathione (AsA-GSH) cycle" may be the effective protector mechanism in xerophytic Caragana species, and that catalase (CAT) may have limited effects under severe stress. Different congener species likewise have differential antioxidant mechanisms to regulate their redox status. It was also determined that drought stress did not induce any new isoenzyme of SOD, POD, and CAT, but that the xerophytic Caragana species considerably have more MnSOD and FeSOD isoenzymes. On the basis of the data obtained, we could infer both C. roborovskyi and C. tragacanthoides plants have more effective complex antioxidant systems against oxidative damage. Free proline may be crucial in the resistance of C.arborescens and C. microphylla to drought stress... |
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