Under fluctuating ambient conditions, the ability of plants to maintain hydromineral homeostasis requires the tight control of long distance transport. This includes the control of radial transport within leaves, from veins to mesophyll. The bundle sheath is a structure that tightly wraps around leaf vasculature. It has been suggested to act as a selective barrier in the context of radial transport. This suggestion is based on recent physiological transport assays of bundle sheath cells (BSCs), as well as the anatomy of these cells. We hypothesized that the unique transport functionality of BSCs is apparent in their transcriptome. To test this, we compared the transcriptomes of individually hand-picked protoplasts of GFP-labeled BSCs and non-labeled mesophyll cells (MCs) from the leaves of Arabidopsis thaliana. Of the 90 genes differentially expressed between BSCs and MCs, 45% are membrane related and 20% transport related, a prominent example being the proton pump AHA2. Electrophysiological assays showed that the major AKT2-like membrane K+ conductances of BSCs and MCs had different voltage dependency ranges. Taken together, these differences may cause simultaneous but oppositely directed transmembrane K+ fluxes in BSCs and MCs, in otherwise similar conditions.
Bibliographical noteFunding Information:
We thank Dr Varda Oron-Karni at the Bioinformatics unit of Tel-Aviv University, Israel, for performing feasibility tests and her advice on RNA extraction issues. Many thanks to Professor Menachem Segal and to Mr Moshe Shmilovich, for solving our patch-clamp equipment problems and to Dr Yossi Wein and Dr Enav Bar-Shira for support in qRT-PCR issues. This research was supported by the Israel Science Foundations, ISF (grants No. 1312/12 and 1842/13 to NM and 1311/12 to MM).
© The Author 2017. Published by Oxford University Press on behalf of the Society for Experimental Biology.
- Arabidopsis thaliana
- Bundle sheath
- C3 plant
- Membrane potential
- Membrane transport
- Patch clamp
- Ratiometric fluorescent probe