Submitted to: International Botanical Congress
Publication Type: Abstract Only
Publication Acceptance Date: 4/18/2005
Publication Date: 7/18/2005
Citation: Richards, J.H., James, J.J., Alder, N.N., Muhling, K.H., Laeuchli, A.E., Donovan, L.A. 2005. High apoplastic solute concentrations in leaves alter water relations of the halophytic shrub sarcobatus vermiculatus [abstract]. International Botanical Congress. Paper No. P1878. Interpretive Summary: Water relations models are used to evaluate competition between plants, to assess drought tolerance of crop and wildland plant species, and to develop more efficient irrigation systems. We used a native, salt-tolerant shrub to test some commonly held assumptions about plant and soil water interactions. Contrary to current thinking, results suggest that plants can maintain high salt ion concentrations in leaf intercellular spaces. The results can be used to refine plant water relations models and will help scientists gain a better understanding of plant and soil water interactions of native and crop plants.
Technical Abstract: It has long been known that many plants, particularly stress tolerant species, fail to equilibrate with soil water potential by dawn. While recent studies show that both nighttime shoot and root water loss can contribute to predawn disequilibrium (PDD), even when these are prevented PDD can be large. We predict that a major mechanism of PDD is high solute concentration in the leaf apoplast. We quantified leaf apoplastic solutes of the desert halophytic shrub, Sarcobatus vermiculatus, which has both large PDD and large discrepancies between predawn leaf and xylem water potentials. Pressure probe and nanoliter osmometer measurements confirmed leaf cell water relations consistent with psychrometric data. Analyses of apoplastic fluid collected by centrifugation showed 80±11—229 ± 36 mM Na+, depending on salinity treatment, plus 50 mM K+ in leaves at dawn. This demonstrates that leaf apoplastic solute concentrations can be very high, explaining discrepancies between leaf and xylem water potentials at dawn, as well as contributing to PDD. High apoplastic solute concentrations affect water relations and mineral nutrition of stress tolerant species with high PDD.