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- Title
High apoplastic solute concentrations in leaves alter water relations of the halophytic shrub, Sarcobatus vermiculatus.
- Authors
James, J. J.; Alder, N. N.; Mühling, K. H.; Läuchli, A. E.; Shackel, K. A.; Donovan, L. A.; Richards, J. H.
- Abstract
Predawn plant water potential (Ψw) is used to estimate soil moisture available to plants because plants are expected to equilibrate with the root-zone Ψw. Although this equilibrium assumption provides the basis for interpreting many physiological and ecological parameters, much work suggests predawn plant Ψw is often more negative than root-zone soil Ψw. For many halophytes even when soils are well-watered and night-time shoot and root water loss eliminated, predawn disequilibrium (PDD) between leaf and soil Ψw can exceed 0.5 MPa. A model halophyte, Sarcobatus vermiculatus, was used to test the predictions that low predawn solute potential (Ψs) in the leaf apoplast is a major mechanism driving PDD and that low Ψs is due to high Na+ and K+ concentrations in the leaf apoplast. Measurements of leaf cell turgor (Ψp) and solute potential (Ψs) of plants grown under a range of soil salinities demonstrated that predawn symplast Ψw was 1.7 to 2.1 MPa more negative than predawn xylem Ψw, indicating a significant negative apoplastic Ψs. Measurements on isolated apoplastic fluid indicated that Na+ concentrations in the leaf apoplast ranged from 80 to 230 mM, depending on salinity, while apoplastic K+ remained around 50 mM. The water relations measurements suggest that without a low apoplastic Ψs, predawn Ψp may reach pressures that could cause cell damage. It is proposed that low predawn apoplastic Ψs may be an efficient way to regulate Ψp in plants that accumulate high concentrations of osmotica or when plants are subject to fluctuating patterns of soil water availability.
- Subjects
SARCOBATUS vermiculatus; PLANT cells &; tissues; CHENOPODIACEAE; SARCOBATUS; VASCULAR system of plants
- Publication
Journal of Experimental Botany, 2006, Vol 57, Issue 1, p139
- ISSN
0022-0957
- Publication type
Article
- DOI
10.1093/jxb/erj016