scholarly journals Arabidopsis leaf hydraulic conductance is regulated by xylem‐sap pH, controlled, in turn, by a P‐type H + ‐ATPase of vascular bundle sheath cells

2021 ◽  
Author(s):  
Yael Grunwald ◽  
Noa Wigoda ◽  
Nir Sade ◽  
Adi Yaaran ◽  
Tanmayee Torne ◽  
...  
Keyword(s):  
Vascular Bundle ◽  
Xylem Sap ◽  
Hydraulic Conductance ◽  
Bundle Sheath ◽  
Leaf Hydraulic Conductance ◽  
Bundle Sheath Cells ◽  
P Type ◽  
Ph Controlled ◽  
Sheath Cells

scholarly journals Arabidopsis leaf hydraulic conductance is regulated by xylem-sap pH, controlled, in turn, by a P-type H+-ATPase of vascular bundle sheath cells

2017 ◽  
Author(s):  
Yael Grunwald ◽  
Noa Wigoda ◽  
Nir Sade ◽  
Adi Yaaran ◽  
Tanmayee Torne ◽  
...  
Keyword(s):  
Proton Pump ◽  
Vascular Bundle ◽  
Xylem Sap ◽  
Hydraulic Conductance ◽  
Bundle Sheath ◽  
List Type ◽  
Mesophyll Cells ◽  
Leaf Hydraulic Conductance ◽  
Bundle Sheath Cells ◽  
Sheath Cells

AbstractThe leaf vascular bundle sheath cells (BSCs) that tightly envelop the leaf veins, are a selective and dynamic barrier to xylem-sap water and solutes radially entering the mesophyll cells. Under normal conditions, xylem-sap pH of <6 is presumably important for driving and regulating the transmembranal solute transport. Having discovered recently a differentially high expression of a BSCs proton pump, AHA2, we now test the hypothesis that it regulates this pH and leaf radial water fluxes.We monitored the xylem-sap pH in the veins of detached leaves of WT Arabidopsis, AHA mutants, and aha2 mutants complemented with AHA2 gene solely in BSCs. We tested an AHA inhibitor and stimulator, and different pH buffers. We monitored their impact on the xylem-sap pH and the whole leaf hydraulic conductance (Kleaf), and the effect of pH on the water osmotic permeability (Pf) of isolated BSCs protoplasts.Our results demonstrated that AHA2 is necessary for xylem-sap acidification, and in turn, for elevating Kleaf. Conversely, knocking out AHA2 alkalinized the xylem-sap. Also, elevating xylem sap pH to 7.5 reduced Kleaf and elevating external pH to 7.5 decreased the BSCs Pf.All these demonstrate a causative link between AHA2 activity in BSCs and leaf radial water conductance.One-sentence summaryBundle-sheath cells can control the leaf hydraulic conductance by proton-pump-regulated xylem sap pH

scholarly journals Stress is basic: ABA alkalinizes both the xylem sap and the cytosol of Arabidopsis vascular bundle sheath cells by inhibiting their P-type H+-ATPase and stimulating their V-type H+-ATPase

2021 ◽  
Author(s):  
Tanmayee Torne ◽  
Yael Grunwald ◽  
Ahan Dalal ◽  
Adi Yaaran ◽  
Menachem Moshelion ◽  
...  
Keyword(s):  
Membrane Potential ◽  
Signaling Pathways ◽  
Xylem Sap ◽  
Bundle Sheath ◽  
List Type ◽  
Stress Hormone ◽  
Isolated Protoplasts ◽  
Leaf Vein ◽  
Bundle Sheath Cells ◽  
Sheath Cells

ABSTRACTBACKGROUND AND HYPOTHESIS•Under water deprivation, in many perennial species, the stress hormone, ABA, appears in the xylem sap in the shoot (including leaf) veins and the xylem sap pH (pHEXT) increases. This study aimed to test the hypothesis that ABA is the signal for an altered proton balance of the leaf-vein-enwrapping bundle sheath cells (BSCs).METHODS•Plant Material. We used a few Arabidopsis thaliana (L.) Heynh. genotypes: wildtype (WT) of two accessions, Landsberg erecta (Ler) and Columbia (Col), and a few mutants and transformants in these backgrounds.•H+-Pumps activities. We monitored ABA effects on the H+-pump activities in the BSCs cytosol-delimiting membranes (plasma membrane and tonoplast) by monitoring the cytosol and the xylem pH, and the membrane potential (EM), by imaging the fluorescence of pH- and membrane potential (EM)-reporting probes: (a) the BSCs’ pHEXT – with the ratiometric fluorescent dye FITC-dextran petiole-fed into detached leaves in unbuffered xylem perfusion solution (XPS), (b) the BSCs’ pHCYT – with the ratiometric dye SNARF1 loaded into BSCs isolated protoplasts, and (c) the BSCs’ EM – with the ratiometric dye di- 8-ANEPPS.RESULTS•ABA increased the pHEXT; this response was abolished in an abi1-1 mutant with impaired signaling via a PP2C (ABI1) and in an aha2-4 mutant with knocked-down AHA2;•ABA depolarized the WT BSCs;•ABA increased pHCYT irrespective of AHA2 activity (i.e., whether or not AHA was inhibited by vanadate, or in the aha2-4 mutant);•The ABA-induced cytosol alkalinization was abolished in the absence of VHA activity (i.e., when VHA was inhibited by bafilomycin A1, or in the vha-a2 vha-a3 double mutant with inactive VHA);•All these results resemble the ABA effect on GCs;•In contrast to GCs, AHA2 and not AHA1 is the ABA major target in BSCs;•Blue light (BL) enabled the response of the BSCs’ VHA to ABA;•The ABA- and BL-signaling pathways acting on both BSCs’ pumps, AHA2 and VHA, are likely to be BSCs autonomous, based on (a) the presence in the BSCs of many genes of the ABA- and BL-signaling pathways and (b) ABA responses (depolarization and pHCYT elevation) demonstrated under BL in isolated protoplasts.SIGNIFICANCE STATEMENTWe reveal here an alkalinizing effect of the plant drought-stress hormone ABA on the pH on both sides of the plasmalemma of the vein-enwrapping bundle sheath cells (BSCs), due to ABA inhibition of the BSCs’ AHA2, the plasmalemma H+- ATPase and stimulation of VHA, their vacuolar H+-ATPase. Since pH affects the BSCs’ selective regulation of solute and water fluxes into the leaf, these H+- pumps may be attractive targets for manipulations aiming to improve plant drought response.

scholarly journals Out of the blue; Phototropins of the leaf vascular bundle sheath mediate the blue light regulation of the leaf hydraulic conductance

2019 ◽  
Author(s):  
Yael Grunwald ◽  
Sanbon Chaka Gosa ◽  
Tanmayee Torne ◽  
Nava Moran ◽  
Menachem Moshelion
Keyword(s):  
Signal Transduction ◽  
Blue Light ◽  
Vascular Bundle ◽  
Vascular Tissue ◽  
Xylem Sap ◽  
Signal Transduction Pathway ◽  
Hydraulic Conductance ◽  
Bundle Sheath ◽  
Transduction Pathway ◽  
Water Permeability Coefficient

ABSTRACTThe leaf vascular bundle sheath cells (BSCs), which tightly envelop the leaf veins, constitute a selective dynamic barrier to water and solutes radially entering the mesophyll and play a major role in regulating the leaf radial hydraulic conductance (Kleaf). Recently, we showed that the BSCs’ plasma membrane H+-ATPase, AHA2, increases Kleaf by acidifying the xylem sap. Since BL reportedly increases Kleaf and we found the blue light (BL) receptor genes, PHOT1 and PHOT2 expressed in the Arabidopsis BSCs, we hypothesized that, similar to the guard cells (GCs) BL signal transduction pathway, the BSCs’ PHOT1 and PHOT2 activate the BSCs’ H+-ATPase and thus regulate Kleaf. Indeed, under BL illumination, the Kleaf in the knockout mutant lines phot1-5, phot2-1, phot1-5phot2-1 and aha2-4 was lower than in WT. BSCs-directed complementation (using the SCR promoter) of phot1-5 and aha2-4 respectively by PHOT1 and AHA2, restored the BL-induced Kleaf increase. BSCs-specific silencing of PHOT1 or PHOT2 (using the SCR promoter) abolished the BL-induced Kleaf increase. Xylem-fed PHOT inhibitor, tyrphostin 9, also abolished the BL-induced Kleaf increase in WT. Moreover, in WT plants, white light (WL) acidified the xylem sap compared to dark, but did not acidify the xylem sap of the phot1-5 mutant. BSCs-specific complementation of phot1-5 by SCR: PHOT1, restored the WL-induced xylem acidification. On a cellular level, BL hyperpolarized the BSCs, which was prevented by tyrphostin 9. In addition, the osmotic water permeability coefficient (Pf) of the BSCs was higher under WL treatment. Our results link the blue light control of water fluxes from the xylem to the mesophyll via the BSCs in the following model:BL →BSCs’ PHOTs activation →tyrosine phosphorylation→BSCs’ H+- ATPase activation →BSCs hyperpolarization, xylem acidification →Pf elevation → Kleaf increase. Thus, this study is the first to demonstrate an independent BL signal transduction pathway regulation of the vascular tissue.

Nitrate metabolism in relation to the aspartate-type C-4 pathway of photosynthesis in Eleusine coracana

1974 ◽  
Vol 52 (12) ◽  
pp. 2599-2605 ◽  
Author(s):  
C. K. M. Rathnam ◽  
V. S. R. Das
Keyword(s):  
Glutamate Dehydrogenase ◽  
Eleusine Coracana ◽  
Bundle Sheath ◽  
Chloroplast Envelope ◽  
Mesophyll Cells ◽  
Bundle Sheath Cells ◽  
Nitrate Metabolism ◽  
Type C ◽  
Envelope Membranes ◽  
Sheath Cells

The intercellular and intracellular distributions of nitrate assimilating enzymes were studied. Nitrate reductase was found to be localized on the chloroplast envelope membranes. The chloroplastic NADPH – glutamate dehydrogenase was concentrated in the mesophyll cells. The extrachloroplastic NADH – glutamate dehydrogenase was localized in the bundle sheath cells. Glutamate synthesized in the mesophyll chloroplasts was interpreted to be utilized exclusively in the synthesis of aspartate, while in the bundle sheath cells it was thought to be consumed in other cellular metabolic processes. Based on the results, a scheme is proposed to account for the nitrate metabolism in the leaves of Eleusine coracana Gaertn. in relation to its aspartate-type C-4 pathway of photosynthesis.

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