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Bundle-sheath cell regulation of xylem-mesophyll water transport via aquaporins under drought stress: a target of xylem-borne ABA?
MedLine Citation:
PMID:  21401747     Owner:  NLM     Status:  Publisher    
Abstract/OtherAbstract:
The hydraulic conductivity of the leaf vascular system (K(leaf) ) is dynamic and decreases rapidly under drought stress, possibly in response to the stress phytohormone ABA which increases sharply in the xylem sap (ABA(xyl) ) during periods of drought. Vascular bundle-sheath cells (BSCs; a layer of parenchymatous cells tightly enwrapping the entire leaf vasculature) have been hypothesized to control K(leaf) via the specific activity of BSC aquaporins (AQPs). We examined this hypothesis and provide evidence for drought-induced ABA(xyl) diminishing BSC osmotic water permeability (P(f) ) via downregulated activity of their AQPs. ABA fed to the leaf via the xylem (petiole) both decreased K(leaf) and led to stomatal closure, replicating the effect of drought. In contrast, smearing ABA on the leaf blade, while also closing stomata, did not decrease K(leaf) within the 2 to 3 h of the experiments, demonstrating that K(leaf) does not depend entirely on stomatal closure. GFP-labeled BSCs showed decreased P(f) in response to 'drought' and ABA treatments, and a reversible decrease with HgCl(2) (an AQP blocker). These P(f) responses, absent in mesophyll cells, suggest stress-regulated AQP activity specific to BSCs and imply a role for these cells in decreasing K(leaf) via reduction in P(f) . Our results support the above hypothesis and highlight the BSCs as hitherto overlooked vasculature sensor compartments, extending throughout the leaf and functioning as 'stress-regulated valves' converting vasculature chemical signals (possibly ABA(xyl) ) into leaf hydraulic signals.
Authors:
Arava Shatil Cohen; Ziv Attia; Menachem Moshelion
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Publication Detail:
Type:  JOURNAL ARTICLE     Date:  2011-3-14
Journal Detail:
Title:  The Plant journal : for cell and molecular biology     Volume:  -     ISSN:  1365-313X     ISO Abbreviation:  -     Publication Date:  2011 Mar 
Date Detail:
Created Date:  2011-3-15     Completed Date:  -     Revised Date:  -    
Medline Journal Info:
Nlm Unique ID:  9207397     Medline TA:  Plant J     Country:  -    
Other Details:
Languages:  ENG     Pagination:  -     Citation Subset:  -    
Copyright Information:
Copyright © 2011 Blackwell Publishing Ltd and the Society for Experimental Biology.
Affiliation:
The Robert H. Smith Institute of Plant Sciences and Genetics in Agriculture, Faculty of Agriculture, Food and Environment, The Hebrew University of Jerusalem, Rehovot 76100, Israel.
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