Physiological Implications and Experimental Testing of the Münch-Horwitz Theory of Phloem Transport

Friday, December 6, 2019 - 2:00pm to 3:15pm


John D. Goeschl


Products of photosynthesis (e.g. sugars etc.) are transported from the leaves to other plant parts through a network of microscopic “Sieve Tubes”, which are the functional elements of the plant’s Phloem Transport Tissues. Ernst Münch’s 1930 ‘Osmotically Driven Pressure Flow’ Hypothesis of Phloem Transport can be expressed in mathematical form, by combining equations suggested by Münch (1930), Horwitz (1958), and Eschrich, Evert and Young (1972), into mathematically consistent steady-state and time-dependent models by this author and colleagues.

The resulting models were then used to predict the behavior of Phloem Sieve Tubes in relation to various physiological conditions in the plant. These predictions lead to a new hypothesis regarding the mechanisms by which plants respond to moderate drought stress, which is considered the most important factor limiting photosynthetic productivity of plants in both agricultural and natural ecosystems
To critically test the models and the hypotheses they represent, we developed an experimental technology and analytic algorithms (i.e. Extended Square Wave Carbon-11 Tracer Kinetics) uniquely designed to provide real-time, non-destructive measurements of all the necessary variables in live, intact plants. Experimental data will be presented that clearly support predictions of the models.