Starch dicots

Mutations of SSIIa have been observed in wheat and rice.208 In wheat, each of the three wheat genomes were mutated to entirely eliminate expression of the SSIIa gene product, Sgp-1 protein in one line 209 the result was reduced starch amounts and an altered starch structure. In rice, two classes of starch have been found. In Indica rices, the starch is of the long chain variety, while in Japonica, it is of the short chain variety.208 Genetic analysis showed that the mutation in Japonica rice led to a loss of starch synthase II.209 Thus, in higher plants, it seems that loss of SSII activity in dicots and SSIIa activity in monocots have the same results with respect to reduced starch content, due to a lowered amount of amylopectin and altered amylopectin chain size distribution. Thus, these genes may have the same function in starch biosynthesis. 

Starch degradation in dicot seeds yields more glucose and maltotriose than that in cereals, where more maltose is produced. This is related, in part, to the relative activity of jS-amylase in the two classes of seeds. 

---