Studies On Ecophysiological Characteristics Of Desiccation-tolerant Mechanism In Desert Resurrection Plant Reaumuria Soongorica

Reaumuria soongorica comes from tertiary, and is one of the representative species in ancient Mediterranean region. It belongs to Tamaricaceae, a perennial semi-shrub, and has the characteristics of dormancy and leaf abscission under desiccation. So it is a resurrection plant in temperature zones and a good material in study plants on drought tolerance. This paper presented the studies on the changes of photosynthetic activities of branches, metabolic products in leaves and stems, morphological characteristics, anatomy and chloroplast ultrastructure, gene expression level in young and mature plants, and MAP kinase signal pathway in R. soongorica under progressive drought stress. The studies were analyzed and discussed to elucidate further the mechanisms of adaptation to desiccation tolerance in R. soongorica. The main results were summarized as follows:1. Pn declined during drought stress in R. soongorica, but intrinsic WUE increased remarkably with increasing drought stress. The maximal photochemical efficiency ofPSⅡ (Fv/Fm) and the quantum efficiency of noncyclic electric transport of PS Ⅱ (ΦPS Ⅱ) decreased significantly under drought stress and exhibited an obvious phenomenon of photoinhibition at noon. Drought stressed plants maintained a higher capacity of dissipation of the excitation energy (measured as NPQ) with the increasing intensity of stress, indicating that the xanthophylls cycle-dependent thermal energy dissipation played the main role during drought stress. This opinion was also supported by the increased content of xanthophyll cycle pigment zeaxanthin. The chlorophyll content had dropped only under severe drought stress. However, when leaf water potential was less than -21.3MPa in mature plants, the leaves died and abscised. But the stem photosynthesis remained and, afterward the plants entered the dormant state. Upon rewatering, the shoots reactivated and the plants developed new leaves. Therefore, R. soongorica has the ability to reduce water loss through leaf abscission and maintain the vigor of the stem cells to survive desiccation.2. Changes of metabolic products in R. soongorica during dehydration showed that the progressive drought stress caused an increase in sucrose accumulation in young and mature leaves and stems, which had a higher accumulation in the stems and decreased.