Blue Gem (Craterostigma plantagineum)

Description

This review will focus on the acquisition of desiccation tolerance in the resurrection plant Craterostigma plantagineum. Molecular aspects of desiccation tolerance in this plant will be compared with the response of non-tolerant plants to dehydration. Unique features of C. plantagineum are described like the CDT-1 (Craterostigma desiccation tolerance gene-1) gene and the carbohydrate metabolism. Abundant proteins which are associated with the desiccation tolerance phenomenon are the late embryogenesis abundant (=LEA) proteins. These proteins are very hydrophilic and occur in several other species which have acquired desiccation tolerance. Most higher plants are unable to survive desiccation to an air-dried state and only seeds and pollen grains can withstand air dryness for certain periods of time. Pollen grains loose tolerance quickly, whereas seeds can stay for longer in the desiccated state (see also contribution by Walters et al., 2005). However, a small group of vascular angiosperm plants termed -resurrection plants- have also evolved desiccation tolerance, and they can revive from an air-dried state. This is the severest form of water stress, since most protoplasmic water is lost from the cell under these conditions. Resurrection plants are able to withstand severe water loss, and some are even able to equilibrate the leaves with air to 0% (v/v) relative humidity (Gaff, 1971, 1987). The resurrection capacity is normally extended to all tissues of the plant. Resurrection plants are mostly poikilohydrous, which means that their water content adjusts with the relative humidity in the environment. They are able to stay in the dehydrated state until water becomes available and allows them to rehydrate and to resume full physiological activities. During the dehydration process leaves of resurrection plants shrink and curl up. Mature tissue of resurrection plants such as leaves and roots, are able to remain in the air-dried state for months by reaching a quiescent state which is comparable with dormancy in seeds in several aspects. Resurrection plants take immediate advantage of rainfall after dry periods: they resurrect, grow and reproduce before other species can do so (Scott, 2000). Studies have shown that the physiological conditions of the plants are critical for the ability to exhibit desiccation tolerance.