Investigation into the ability of roots of the poikilohydric plant Craterostigma plantagineum to survive dehydration stress

Abstract

The ability of the root system of the poikilohydric plant Craterostigma plantagineum to survive dehydration was investigated. The data presented here reveal that the root system is capable of surviving dehydration, but shortly after rehydration the root system senesces. Two weeks after rehydration the growth of a complete new root system is initiated. During dehydration sucrose accumulates from 36 to a maximum of 111 micromol g-1 DW in the roots. It is suggested that the accumulation of sucrose protects the root system during dehydration. There are major stores of stachyose in the roots of Craterostigma (making up over 40% of the dry weight of the tissue) and during dehydration these stores are metabolized. It is suggested that these stachyose stores act as carbohydrate reserves for the synthesis of sucrose. However, over 350 micromol g-1 DW stachyose is metabolized in the roots, which is well in excess of that required for the accumulation of sucrose observed. It is likely that the stachyose reserves in the root system are translocated to other regions of the plant to support carbohydrate metabolism during dehydration of the tissue. During rehydration, the stachyose reserves return to their original level within 96 h. There is no change in the elevated sucrose content of the roots over this period. Thus the roots maintain the protective properties of sucrose much longer than they are needed. The maintenance of high sucrose contents in rehydrating roots is discussed as a possible survival strategy against recurrent desiccation events.

Molecular mechanisms of desiccation tolerance in the resurrection glacial relic Haberlea rhodopensis

“…Raffinose-family oligosaccharides (RFOs) such as raffinose and stachyose, also accumulate during desiccation in many angiosperm resurrection plants and may have prominent roles protecting the cells by water replacement and vitrification [66]. Raffinose is synthesized by raffinose synthase from galactinol and sucrose [67].…”

“…The activation of many heat shock transcription factors in H. rhodopensis by drought stress is further supported by the induction of heat shock protein genes. Raffinose family oligosaccharides have also been speculated to be possible sources of carbon for sucrose synthesis [66]. The strong induction of stachyose synthase in water-deficient samples implies involvement of RFOs in the acquisition of tolerance against drought stress and desiccation, a notion supported by the accumulation of the RFO member verbascose.…”

Constraints of tolerance: why are desiccation-tolerant organisms so small or rare?

“…Sugars may accumulate to very high levels. For example, sugars associated with desiccation tolerance can make up over 40% of the mass of the tolerant plant Craterostigma plantagineum (Norwood et al, 2003;Bartels, 2005). In some tolerant species, desiccation induces the expression of hundreds of genes, including LEA genes, whose proteins may act as chaperones for other proteins and interact with sugar to immobilize dry cytoplasm (Goyal et al, 2005a), and small stress proteins that can increase the effectiveness of LEA proteins and trehalose (Crowe et al, 2005;Ma et al, 2005).…”

Ecology of Water Relations in Plants

“…Poikilohydric plants show an ability of mature tissues such as the shoot, stem and leaves to tolerate almost complete dehydration of the tissues and then return as functional units very rapidly on rehydration, sometimes in as short as 24 hours (Norwood, et al 2003). Obviously, such plants are native to and inhabit ecological niches that are subjected to lengthy periods of drought with brief periods of rain during the year e.g.…”