Source of Assimilates for Starch Formation

There is still considerable debate as to whether sucrose can be transported from the phloem into the developing endosperm in an unmodified form, or whether it must first be hydrolysed to glucose and fructose and then resynthesized into the disaccharide. The funiculus-chalazal region of Zea mays shows increased invertase activity at about the time when starch synthesis commences in the endosperm [163], and this is associated with an increase in free hexoses in this region. One current hypothesis [155] favours the cleavage of sucrose during 

Starch deposition begins in the region of the furrow (the region nearest the sucrose source) after cell division in the endosperm ceases. The young endosperm cells have prominent nuclei, numerous mitochondria, endoplasmic 

Transverse sections of developing grains — all to same scale 

Diagrams showing development of endosperm including crease formation 

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