TRANSPORT AND DISTRIBUTION OF C-14 ASSIMILATES IN WHEAT GENOTYPES WITH VARIOUS PHOTOSYNTHETIC CHARACTERISTICS AND ECONOMIC YIELDS

The upper three leaves of winter wheat plants with contrasting photosy nthetic characteristics were exposed to (CO2)-C-14 during either the f lowering or seed ripening phases, and the consequent distribution of l abeled assimilates in different plant parts was determined one day aft er exposure and at the end of the growth period. When leaves were labe led in the flowering phase, a significant portion of the label was fou nd in the stem as soon as 24 h after labeling. Unlike tall plant varie ties, the plants of an intensive dwarf variety accumulated the most of the label in the top internode. The dwarf variety plants accumulated 22% of the label in the ear, whereas only 5-7% of the assimilates were found in the ears of tall varieties. In the subsequent period, until full ripening of the caryopses, the portion of C-14 in the ear increas ed to 70% at the expense of assimilates remobilized from the stem and the fed leaves. The ears of the dwarf variety contained 10-20% more as similates than the ears of tall varieties. When (CO2)-C-14 was fed at the phase of milky ripeness, the most rapid export of assimilates from leaves and the largest import of assimilates into ears (70%) were obs erved during the first day, indicating an increased sink activity of e ars in this phase. It is concluded that, at the early phases of reprod uctive growth, the dwarf plants allocate assimilates more efficiently for the purpose of grain formation than for vegetative organ developme nt; lower leaves of these plants participate more actively in grain fi lling.