S. Alam et al., Metal micronutrients in xylem sap of iron-deficient barley as affected by plant-borne, microbial, and synthetic metal chelators, SOIL SCI PL, 47(1), 2001, pp. 149-156
A greenhouse experiment was conducted to study the effects of phytosideroph
ore (PS), deferriferrioxamine B (Desferal), and ethylene diamine tetraaceti
c acid (EDTA) on the concentrations of copper (Cu), iron (Fe), manganese (M
n), and zinc (Zn) in the xylem sap of Fe-deficient barley (Hordeum vulgare
L, cv. Minorimugi) plants grown in 1/2-strength modified Hoagland-Arnon nut
rient solution. Iron-deficient plants (14 d after transfer) were treated wi
th 25 muM metal chelators for 3 h after which the xylem sap was collected f
or 3 h, Treated plants were compared with Fe-sufficient and untreated Fe-de
ficient plants. The concentration and translocation of PS, Mn, and Zn incre
ased, while those of Fe decreased in xylem sap of the Fe-deficient plants c
ompared to the Fe-sufficient plants. The concentrations of PS, Cu, Fe, Mn,
and Zn in the xylem sap of the Fe-deficient plants increased by the applica
tion of PS to the nutrient solution. This fact suggested that PS solubilize
d the metal micronutrients in the root tissues and/or root apoplast and con
tributed to the loading of the nutrients to the xylem tubes, thereby leadin
g to a higher nutrient absorption from the rhizosphere of Fe-deficient plan
ts. On the other hand, Fe-deficient plants treated with EDTA showed a decre
ase in the PS, Cu, Fe, Mn, and Zn concentrations in the xylem sap, Applicat
ion of Desferal to the nutrient solution slightly increased only the Fe con
centration in the xylem sap of the Fe-deficient plants. Organic acids in th
e xylem sap of the Fe-deficient plants were in the order of succinate > mal
ate > citrate based on the concentrations, and did not appear to be related
to the translocation of metal micronutrients.