Introduction Role of Nonreducing Disaccharides in Plants

Nonreducing disaccharides provide a soluble energy source in the form of a stable molecule that can also function as a protectant compound under stress conditions in all organisms except vertebrates. Trehalose and sucrose are the two sugars that perform this role.

The components of reducing sugars, glucose in the case of trehalose and glucose and fructose in the case of sucrose, are linked at their reducing ends. In naturally occurring trehalose, the two glucose units are linked in a a, a-1,1 configuration. Isomers include neotrehalose with an a,b link, and isotrehalose, which has a p,p link. In sucrose, fructose and glucose are linked in an a,b-1,2 configuration. Both configurations produce stable energy molecules (Fig. 14.1).

Plants are unique in that they can synthesize both the nonreducing disaccharides, but sucrose performs the main role of translocated sugar in plants. Trehalose is found in millimolar amounts in only a few plants, namely, resurrection species, where it is thought to protect against desiccation.

OH HO

Sucrose (a,p- 1,2 configuration)

OH HO

Sucrose (a,p- 1,2 configuration)

CH2OH

hoh2c

CH2OH

hoh2c

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