Upregulating starch biosynthesis in leaves (this study) and in developing
grain of rice may be beneficial. Increases in biomass and
seed yields have also been observed by seed-specific expression
of up-regulated AGPase genes in rice [28,29] and wheat [30]. Interestingly,
the increases in seed yields in these studies were due to a
greater number of grains produced and not to a greater grain size
as would be expected if starch synthesis during endosperm development
was stimulated. Moreover, in addition to this unexpected
transgene effect, the reason for the increases in vegetative biomass
and reproductive organs remain unresolved as these plants organs
are developed well before the onset of the expression of the introduced
transgene during seed development. These studies are in
contrast to that of Sakulsingharoj et al. [31] in which there was
an increase in seed size when a bacterial up-regulated AGPase is
expressed during endosperm development.