Supplementary Material to

1. Animation Supplementary Material to P. Gajdanowicz, E. Michard, M. Sandmann, M. Rocha, L.G. Guedes Corrêa, S.J. Ramírez-Aguilar, J.L. Gomez-Porras, W. Gonzalez, J.-B. Thibaud, J.T. van Dongen, I. Dreyer K+ gradients serve as a mobile energy source in plant vascular tissues dreyer@uni-potsdam.de

2. The K+gradient serves as an energy sourcefor phloem (re)loading S S S S S S H+ H+ H+ H+ H+ H+ K+ • 1) In source tissues, photoassimilates (S) and K+ ions are transported into the phloem by consuming chemical energy (ATP): • H+/S symporters use the energy of the electrochemical H+ gradient established by H+-ATPases to accumulate S to high concentrations in the phloem

3. The K+gradient serves as an energy sourcefor phloem (re)loading S S S H+ H+ K+ K+ • 1) In source tissues, photoassimilates (S) and K+ ions are transported into the phloem by consuming chemical energy (ATP): • H+/S symporters use the energy of the electrochemical H+ gradient established by H+-ATPases to accumulate S to high concentrations in the phloem • K+-uptake channels use the electrical gradient established by H+-ATPases

4. The K+gradient serves as an energy sourcefor phloem (re)loading S S S S H+ H+ H+ H+ K+ S S S 2) During the transport from source to sink tissues, photoassimilates are “leaking” from the transport phloem and also undergo metabolic modifcations (B.G. Ayre et al., 2003, Plant Physiol. 131, 1518-1528) 3) Reloading of photoassimilates is (under normal conditions) energized by ATP-consuming H+-ATPases

5. The K+gradient serves as an energy sourcefor phloem (re)loading S S H+ H+ K+ S 4) A critical parameter in this re-uptake process is the availability of ATP. ATP has to be produced by local cellular respiration. 5) “Respiration is particularly endangered in transport phloem, which is often deeply embedded in heterotrophic tissues.” (A.J.E. van Bel, 2003, Plant Physiol. 131, 1509-1510; J.T. van Dongen et al. 2003, Plant Physiol. 131, 1529–1543) How can the plant bridge temporarily and locally low ATP levels?

6. The K+gradient serves as an energy sourcefor phloem (re)loading S S H+ H+ K+ S S 4) A critical parameter in this re-uptake process is the availability of ATP. ATP has to be produced by local cellular respiration. 5) “Respiration is particularly endangered in transport phloem, which is often deeply embedded in heterotrophic tissues.” (A.J.E. van Bel, 2003, Plant Physiol. 131, 1509-1510; J.T. van Dongen et al. 2003, Plant Physiol. 131, 1529–1543) How can the plant bridge temporarily and locally low ATP levels?

7. The K+gradient serves as an energy sourcefor phloem (re)loading S H+ H+ H+ H+ K+ K+ K+ S S S • 6) The plant can bridge temporarily and locally low ATP levels by using the K+-gradient. • The AKT2 channel must be converted into a non-rectifying (open) K+ channel. • The K+-gradient is established by the high K+-concentration in the phloemAND locally by the surrounding cells that absorb K+ from the apoplast. Conclusion: Independent of the local ATP level, there is always a K+ gradient that can be harvested for phloem reloading by the AKT2 channel.

8. Some further background: How can a K+gradient drive H+/sugar transport? Step by step m An open K+ channel allows a K+ ion to permeate along its electrochemical gradient. In the present case: From the phloem to the apoplast. m As a consequence of this charge-transport the membrane potential gets inside more negative. H+ K+ S - m This more negative potential provokes an attractive force for positive charges in the apoplast, e.g. for protonated water molecules. SE/CC apoplast m An active H+/S symporter can now canalize this force by allowing a coupled H+/S influx into the phloem. m This charge transport restores the membrane potential. m In reality, K+ efflux and H+/S influx occur simultaneously. Thus, this electro-neutral K+ vs. H+/S antiport does not affect the membrane potential.