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Dhn1 or Dhn2 (YSK2)

Paf93 I

The YSK2-dehydrin from maize seeds shows the typical structure of a dehydrin with Y-and K-consensus sequences (A). The number of serine residues in the S-segment is variable. 0 indicates less conserved sequences, which may be repetitive in individual dehydrins (after Close 1997). B shows dehydrins from barley with different combinations of the conserved motifs: YSK2, SK3, and K9 (after Campbell and Close 1997).

can accumulate in "protein bodies", but also can stabilise cellular membranes by preventing the disintegration of the bilayer into lipid droplets (hexagonal structure of lipids; see Fig. 1.3.16) upon attenuation of the stabilising water film. The hydrophobic stretches of the amphiphilic a-helices interact with the surface of the membranes, whilst the hydrophilic parts are oriented towards the cytoplasm (see Fig. 1.3.24). Preventing the formation of globular lipid structures, they have been called "reversible chaperones". Protection of membranes with dehydrins hinders the accumulation of low-molecular ions at the membrane surface upon withdrawal of cellular water which would result in a change of the membrane potential of that membrane. Dehydrins are very suitable for genetic transforma-

| Table 1.5.1. Growth of rice plants, transformed with the HVA1 gene from barley under drought stress. The plants were exposed to several cycles, each consisting of 5 days of drought and 2 days of recovery. Leaf growth was measured before, and 3 days after, the onset of drought. Leaf growth rates of the two youngest leaves were measured. The height of the plants was measured after four stress cycles and an additional 2 days of recovery (Xu et al. 1996)

Line

Leaf growth

Height of

Root fresh

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