Phloem Translocation of Organic Compounds: A Possible Mechanism to Assist Osmotically-Generated Pressure Flow in Tall Trees
Johnson RJ1* and Canny MJ2
1Independent researcher, Oxford, UK
2Plant Science Division, Research School of Biology, RN Robertson Building, The Australian National University, Canberra, ACT 0200, Australia
*Correspondence E-mail: [email protected]
Key Words: phloem translocation, Münch osmotically-generated pressure flow, EZ layer, Coulomb repulsion, Canal Transport Model
Received September 12th, 2012; Accepted December 30th, 2012; Published January 5th, 2013; Available online January 15th, 2013
Abstract
A supplementary model of phloem translocation is postulated to work in tandem with the Münch osmotically-generated pressure flow (OGPF) model in order to reduce the high pressures required by the OGPF model for flows in tall trees. The supplementary model relies on the assumption that the known symport of protons during solute loading into the phloem is maintained during transport along the sieve-tube elements. Evidence is brought forward in support of each of the necessary components of the postulated Canal Transport Model. Contrary indicators are also discussed and experimental tests of the hypothesized model are suggested. It is hoped that the evidence presented may contribute to the ongoing debate about the pressure flow hypothesis.