PLANT PHYSIOLOGY , Vol 101, Issue 2 391-398, Copyright © 1993 by American Society of Plant Biologists
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DEVELOPMENT AND GROWTH REGULATION |
A Kinetic and Microautoradiographic Analysis of [14C]Sucrose Import by Developing Wheat Grains
D. B. Fisher and N. Wang
Department of Botany, Washington State University, Pullman, Washington 99164
Assimilates enter developing wheat grains via a strand of phloem extending
along the crease region of the grain. After phloem unloading, they move
several hundred micrometers before being released into the endosperm
cavity, from which they are absorbed by the developing endosperm.
Extraphloem assimilate pools in the maternal tissue of the crease,
therefore, play a central role in post-phloem transport. We investigated
the location and turnover of 14C-assimilates in the crease tissues and
endosperm cavity sap by pulse labeling the flag leaf with 14CO2. Sucrose
accounted for >90% of 14C at all times. Kinetic analysis of the crease
sucrose pool and its depletion in excised grains showed that virtually the
entire sucrose content of the crease tissues was involved in post-phloem
transport and behaved basically as a single well-mixed compartment.
Microautoradiographs also showed rapid movement of 14C throughout most of
the crease tissues. Quantification of 14C concentration in the tissues
showed a relatively shallow gradient of 14C and, presumably, of sucrose
through the nucellus and chalaza. The steepest gradient in 14C content
occurred in the vascular parenchyma between the chalaza and conducting
cells (xylem and phloem).
