Journal of Experimental Botany, Vol 49, 1863-1868, Copyright © 1998 by Oxford University Press
M Blom-Zandstra, S Vogelzang and B Veen
The sodium transport and distribution of sweet pepper (Capsicum
annuum L.) under saline conditions were studied after
transferring the plants to a sodium-free nutrient solution. Sodium stress
up to 60 mM did not affect the growth of sweet pepper, as it appears able
to counteract the unfavourable physiological effects of sodium efficiently.
Sodium was particularly accumulated in the basal pith cells of the stem and
in the root cells, while almost no sodium was directed to the leaves or the
fruits. The sodium concentration in the pith cells and xylem sap gradually
decreased towards the shoot tip. Removal of sodium from the medium resulted
in a 50% release of sodium from the plant after 1 week without affecting
the gradient in the pith cells. In contrast, the concentration profile in
the xylem sap was completely changed: the sodium concentration in the xylem
sap at the stem base was similar to that at the top.Phloem transport was
studied in a split root experiment, in which both portions of the roots
were exposed to 15 mM NaCl and one part was fed with additional
22NaCl. During continuous exposure to 15 mM NaCl no
label was detected in unlabelled root parts. However, after transferring
the plants to a sodium-free solution, 22Na was
rapidly released from the unlabelled roots, indicating a downward phloem
transport.It was concluded that pith cells, the intermediates between the
xylem and phloem, play a decisive role in the recirculation of sodium
throughout the plant. Release of sodium from the plants following transfer
to a sodium-free solution may be explained by changes in the diffusion
resistance for passive sodium efflux from the cells.Key
words: Xylem, phloem, sodium, fluxes, sweet pepper
ARTICLES
Sodium fluxes in sweet pepper exposed to varying sodium concentrations
DLO-Research Institute for Agrobiology and Soil Fertility (AB-DLO), PO Box 14, 6700 AA Wageningen, The Netherlands; Corresponding author e-mail: m.blom-zandstra@ab.dlo.nl
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