The Role of Compatible Solutes in Plant Freezing Tolerance: a Case Study on Raffinose

摘要

Compatible solutes are synthesized by many organisms ranging from bacteria to animals and plants, in response to desiccation, osmotic stress, salt stress or low temperature. This chemically heterogeneous group of substances comprises some amino acids(e.g. proline), quaternary ammonium compounds (e.g. betaine), many sugars, sugar alcohols and several others (see Yancey et al., 1982; Somero, 1992, for reviews). The functional role of sugars in cellular desiccation tolerance, however, has recently beenchallenged (Tunnacliffe and Lapinski, 2003), since it has been shown that some organisms are extremely desiccation tolerant without producing elevated amounts of sugars such as sucrose (Sue) or trehalose (Lapinski and Tunnacliffe, 2003). Nevertheless, there is a wealth of information in the literature on the stabilizing effects of various sugars on biological molecules, cells and organisms, which indicates a functional role of sugars in the stress tolerance of many, although not all, organisms. In thischapter, we review the possible role of raffi-nose (Raf) and raffinose family oligosaccharides (RFO) in plant stress tolerance, and in particular in plant freezing tolerance. It should, however, be noted that natural stress tolerance in any organism cannever be explained by the action of just one compound and that in addition to sugar synthesis, many other physiological adaptations have to take place to allow an organism to survive extremes of stress such as freezing or desiccation (see Oliver et al., 2001, 2002, for recent reviews).