ASSIMILATE DISTRIBUTION AND UTILIZATION IN MAIZE

Abstract

The dynamics of distribution and utilization of assimilates from three leaf positions, i.e. the ear leaf (0) and the third leaves above (+3) and below (−3) the ear leaf, in a maize canopy were determined for plants labelled with ¹⁴CO₂ at 10 days after silk emergence. The initial rate of translocation of assimilates (principally sugars) from leaf blades increased with the height of the leaf in the crop canopy. However, by 21 days after labelling no differences in ¹⁴C retention among leaf positions were evident. Sugars from source leaves were gradually utilized in the synthesis of starch and residual matter (principally protein and structural carbohydrate) as they were distributed throughout the plant. Carbon incorporated by the −3 leaf was recovered in free amino acids plus amides and organic acids to a greater extent than that incorporated by the +3 or 0 leaves. Temporary storage of sugars in stem tissue was evident for all three labelled-leaf treatments; the sugars were ultimately used in the synthesis of starch, lipid plus pigment and residual matter of kernels. Some carbon incorporated by lower leaves appeared to be cycled through the root system, possibly being returned to the shoot in organic nitrogen compounds.