20
Production-Related Assimilate Transport and
Partitioning
John E. Hendrix
Colorado State University, Fort Collins, Colorado
421I. INTRODUCTION
The prime assimilatory process is photosynthesis. Assimilation products must be transported to a plant
part (sink) if it is to grow. It is important to maximize the proportion of total assimilate pool that is parti-
tioned into plant parts that are harvested for their economic value. Therefore, any procedure one might
use to enhance partitioning of assimilate into these sinks will serve to increase economic gain. This in-
volves production of assimilates, loading of assimilates into phloem, their transport through phloem
(translocation), and their unloading from phloem into appropriate sinks and incorporation into sink ma-
terials. Also, if pesticides are to be used in the most effective and benign manner, their transport must be
understood.
If phloem function and assimilate partitioning are to be related to crop productivity, several questions
must be addressed:
How are materials partitioned among plant parts?
What materials are translocated and why these and not others?
What are the rate and velocity of assimilate translocation?
What is the mechanism of translocation through sieve tubes?
How are materials loaded into and unloaded from sieve tubes?
What is the mechanism of xenobiotic transport?
How are these processes controlled?Then we must learn how genetics and environment interact to control partitioning. It is apparent that the
study of gene expression and activity as well as control of proteins coded for by these genes is becoming
critical in our efforts to advance understanding of crop productivity.
These topics are not fully understood, but they have been studied extensively and discussed in sev-
eral reviews and symposium publications (see, e.g., Refs. 1–10). The effort here is directed toward relat-
ing these topics to crop productivity.