QUANTITATIVE DISTRIBUTION OF ASSIMILATES IN COMPONENT ORGANS OF MAIZE DURING REPRODUCTIVE GROWTH

Abstract

Maize plants were grown under nutrient culture in the field at 44,400 plants/ha, in individual containers buried in the soil, to study the quantitative distribution of dry matter (DM), sugars, free amino acids plus amides, starch and residual matter (principally structural carbohydrate, protein and mineral matter) in component organs, including roots, during reproductive growth. The rate of development of these plants was faster than that of soil-grown, border-row plants seeded on the same day; silk emergence was advanced by 10 days. In the 15 days after tassel emergence, root dry weight increased from 11.4 to 25.6 g. The shoot-to-root ratio was 5.4 at tassel emergence and had doubled by grain maturity. Whole-plant DM contained approximately 23% sugars and 2% starch during the early stages of grain development, but with advancing maturity, sugar concentration declined to 8% whereas starch concentration increased to 16%. The proportions of DM in the free amino acid plus amide and residue fractions remained at about 4 and 69%, respectively, during grain filling. Although the concentration of sugars in the cob-plus-grain DM declined from 36 to 9% between 10 and 31 days after silking, the quantity of sugars remained constant. During the same period, the concentration of starch in the DM of the cob plus grain increased from 6.5 to 41.3%. The concentration of sugars in leaf DM decreased basipetally, and generally with time, throughout the grain-filling period. The concentration of sugars in stem DM increased during early kernel growth and then declined; the relative decline increased with successive internodes up the stem. The concentration of free amino acids plus amides was greatest in organs of the lower part of the plants. Root DM contained concentrations of free amino acids plus amides approximately twice that of sugars throughout the study; sugars were always less than 5% of root DM and their concentration declined towards grain maturity. Vegetative organs always contained less than 2% DM as starch.