Metabolic changes in leaves and roots during dehydration of the resurrection plant Craterostigma plantagineum (Hochst)

The ability of the resurrection plant Craterostigma plantagineum to recover from complete dehydration has been attributed, in part, to the accumulation of large quantities of sucrose. Correlative studies have suggested that sucrose synthesised in the aerial tissues during dehydration is derived from 2-octulose (Bianchi et al. 1991). We have examined the response of leaves at different developmental stages to dehydration in terms of their survival rates, and measured amounts of the carbohydrates, fructose, glucose, sucrose, rafftnose and stachyose as well as the enzymes aldolase and glyceraldehyde 3-phasphate dehydrogenase. We report that not all leaves of Craterostigma survive the dehydration process during a resurrection cycle. The older leaves exhibit greater sensitivity to drought stress than the other leaves and they die during the phase where leaf water content falls most rapidly. In addition, there was evidence of a dramatic fall in the activity of the enzymes measured in these leaves. Amounts of 2-octulose were higher than all the other sugars, but were substantially lower than previously reported, making it improbable that 2-octulose is the principal source of carbon for sucrose synthesis during dehydration. Measurements of sugars in Ihe roots during partial dehydration suggest that mobilization of root reserves may contribute to sucrose accumulation in the aerial tissues during dehydration. It is also suggested that photosynthesis and the mobilisation of reserves from older senescing leaves may serve as a further source of sucrose