BioProject

The bundle sheath cells (BSCs) layer – a presumed control point for radial transport of water and solutes between the vasculature and the leaf mesophyll cells (MCs) – is still largely understudied. More...

The bundle sheath cells (BSCs) layer – a presumed control point for radial transport of water and solutes between the vasculature and the leaf mesophyll cells (MCs) – is still largely understudied. Using isolated protoplasts, we found that 45% of the 90 genes differentially expressed in BSCs vs. MCs are membrane related and 20% are transport related, suggesting unique functionality of membrane transport in the BSCs, supported also by functional assays (electrophysiology and fluorescence imaging). A tight control of long distance transport is required for the optimization of the hydro-mineral homeostasis of organs in plants under fluctuating ambient conditions. The mechanism of ion selectivity and absorption from the xylem to the leaf is still poorly understood. The bundle sheath (BS), tightly enwrapping the leaf vasculature, has been suggested as a part of this mechanism, acting as a selective barrier which regulates the radial transport of water and solutes from the xylem to leaf cells. This suggestion relies on the anatomy, as well as on the recent physiological transport assays of the BS and its cells (BSCs). We hypothesized that the unique transport functionality of the BSCs is manifested in its transcriptome. To test this, we compared the transcriptomes of individually hand-picked protoplasts of GFP-labeled BSCs and non-labeled mesophyll cells (MCs) of Arabidopsis thaliana leaves. Indeed, in conformation of our hypothesis, 45% of the 90 genes differentially expressed in BSCs vs. MCs are membrane related and 20% are transport related, with the proton-pump AHA2 as a prominent example. Moreover, fluorescence imaging using the potentiometric dye (di-8 ANEPPS) revealed a more negative membrane potential of the BSCs protoplasts compared to those of MCs, and electrophysiological assays (patch-clamp) showed that the major, AKT2-like, membrane K+ conductances of BSCs and MCs had different voltage dependency ranges. Combined, these differences are compatible with an expected possibility of simultaneous but oppositely directed transmembrane K+ fluxes in BSCs and MCs in otherwise similar conditions. Overall design: 6 Samples (arrays) were performed. We generated pairwise comparison between the 2 different cell types (triplicates) using Partek Genomics Suite. Less...