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Plant Physiol, March 2001, Vol. 125, pp. 1419-1428
Salinity-Induced Inhibition of Leaf Elongation in Maize Is
Not Mediated by Changes in Cell Wall Acidification
Capacity1
Beatriz G.
Neves-Piestun and
Nirit
Bernstein*
Institute of Soil, Water, and Environmental Sciences, The Volcani
Center, P.O. Box 6, Bet-Dagan, 50-250, Israel
The physiological mechanisms underlying leaf growth inhibition
under salt stress are not fully understood. Apoplastic pH is considered
to play an important role in cell wall loosening and tissue growth and
was demonstrated to be altered by several growth-limiting environmental
conditions. In this study we have evaluated the possibility that
inhibition of maize (Zea mays) leaf elongation by
salinity is mediated by changes in growing cell wall acidification capacity. The kinetics of extended apoplast pH changes by leaf tissue
of known expansion rates and extent of growth reduction under stress
was investigated (in vivo) and was found similar for non-stressed and
salt-stressed tissues at all examined apoplast salinity levels (0.1, 5, 10, or 25 mM NaCl). A similar rate of spontaneous
acidification for the salt and control treatments was demonstrated also
in in situ experiments. Unlike growing cells that acidified the
external medium, mature nongrowing cells caused medium alkalinization.
The kinetics of pH changes by mature tissue was also unchanged by salt
stress. Fusicoccin, an enhancer of plasmalemma H+-ATPase
activity level, greatly stimulated elongation growth and acidification
rate to a similar extent in the control and salt treatments. That the
ability of the growing tissue to acidify the apoplast did not change
under same salt stress conditions that induced inhibition of tissue
elongation rate suggests that salinity does not inhibit cell growth by
impairing the acidification process or reducing the inherent capacity
for cell wall acidification.
1
This work was supported by the U.S.-Israel
Binational Agriculture Research and Development Fund (grant no.
2360-93). This paper is contribution no. 610/00 from the Volcani
Center, Bet-Dagan, Israel.
*
Corresponding author; e-mail nirit{at}volcani.agri.gov.il; fax
972-3-9604017.
© 2001 American Society of Plant Physiologists
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