Biological systems use transporter proteins to create concentration gradients for a variety
of purposes. In plant, sucrose transporter proteins play a vital role in driving fluid
flow through the phloem by generating chemical potential. In this study, we investigate
these nanoscale phenomena of protein directed active transport in a microscale biological
system. We presented a mathematical model for protein facilitated sucrose loading
considering six different states of the sucrose transporter protein. In addition, we developed
a quasi-one dimensional transport model to study protein facilitated pumping mechanisms
in plant phloem. Here we specifically study the influence of transporter protein
reaction rates, apoplast proton concentration, membrane electrical potential, and cell
membrane hydraulic permeability on flow through the phloem. This study reveals that
increasing companion cell side deprotonation rate significantly enhances the sieve tube
sugar concentrations, which results in much higher water transport. Lower apoplast pH
increases the transport rate, but the flow control is less noticeable for a pH less than 5. A
more negative membrane electrical potential difference will significantly accelerate the
transporter proteins’ ability to pump water and nutrients. Higher companion cell and
sieve element membrane hydraulic permeability also promotes flows through the phloem;
however, the flow difference is less noticeable at higher permeabilities when near typical
plant cell membrane ranges