boost the expression of storage proteins, but also to upregulate
endo-xyloglucan transferase and xyloglucan endotransglycosidase
(XET) (Cosgrove, 1997), both of which are involved in the incor-
poration of newly secreted xyloglucans into cell walls (Nishitani
and Tominaga, 1992; Fry et al., 1992; Wu and Cosgrove, 2000).
This expression is correlated with the upregulation of genes
coding for various elements of the cytoskeleton associated with
growth, such as the alpha and beta subunits of tubulin, and various
actin-depolymerizing factors. Many physiological studies indicate
that expression of these genes may contribute to increased leaf
size at elevated CO2 concentrations (Ferris et al., 2001).