Flux through Cellulose Synthase

Kirretic irrformatiorr orr cellulose synthesis is scarce in the literature. The in vitro studies reported are limited almost exclusively to experimental systems, such as bacteria and elongating cotton and flax fibers (Alorri et al. 1982 Delmer et al. 1993 Li et al. 1993). Li et al. (1993), analyzing cellulose synthase activity in cotton fibers, reported the and for UDP-glucose to be respectively 0.4 mM and 2.8 rrmol min mg protein. If cellulose synthase exhibits similar properties in vivo then it must operate under substrate-saturated conditions since the concentration of UDP-glucose in the cytosol is 13 mM (Dancer et al. 1990 Krause and Stitt 1992 Winter et al. 1993,1994). 

True estimates of for cellulose synthase, however, are still problematic. Delmer (1993, personal communications), for example, has noted that the rates for cellulose synthesis in vitro reported by Li et al. (1993) were no more than 5% of those occurring in vivo during primary wall synthesis. 

An estimate of the carbon flux into cellulose could also be drawn based on an average value of net primary productivity (NPP) for crops, which can also be expressed on a leaf area basis. According to Leopold and Kriedemann (1975), a reasonable growth rate for sunflower leaves could be 85 g dry wt m week. For maize, an average NPP value calculated from results pubhshed by Uhart and Andrade (1995) resulted in 56 g dry wt m week . Averaging these two 

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