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Light-Induced Changes in Hydrogen, Calcium, Potassium, and
Chloride Ion Fluxes and Concentrations from the Mesophyll and Epidermal
Tissues of Bean Leaves. Understanding the Ionic Basis of Light-Induced
Bioelectrogenesis1
Sergey Shabala* and
Ian Newman
School of Agricultural Science (S.S.), and School of Mathematics
and Physics (I.N.), University of Tasmania, G.P.O. Box 252-54, Hobart,
Tasmania 7001, Australia
Noninvasive, ion-selective vibrating
microelectrodes were used to measure the kinetics of H+,
Ca2+, K+, and Cl fluxes and the
changes in their concentrations caused by illumination near the
mesophyll and attached epidermis of bean (Vicia faba L.). These flux measurements were related to light-induced changes in
the plasma membrane potential. The influx of Ca2+ was the
main depolarizing agent in electrical responses to light in the
mesophyll. Changes in the net fluxes of H+, K+,
and Cl occurred only after a significant delay of about 2 min, whereas light-stimulated influx of Ca2+ began within
the time resolution of our measurements (5 s). In the absence of
H+ flux, light caused an initial quick rise of external pH
near the mesophyll and epidermal tissues. In the mesophyll this fast alkalinization was followed by slower, oscillatory pH changes (5-15
min); in the epidermis the external pH increased steadily and reached a
plateau 3 min later. We explain the initial alkalinization of the
medium as a result of CO2 uptake by photosynthesizing
tissue, whereas activation of the plasma membrane H+ pump
occurred 1.5 to 2 min later. The epidermal layer seems to be a
substantial barrier for ion fluxes but not for CO2
diffusion into the leaf.
1
This work was supported by an Australian Research
Council grant to I.N.
*
Corresponding author; e-mail sergey.shabala{at}utas.edu.au; fax
61-3-6226-2642.
Plant Physiol. (1999) 119: 1115-1124
Copyright Clearance Center: 0032-0889/99/119//10
© 1999 American Society of Plant Physiologists
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