PLANT PHYSIOLOGY , Vol 102, Issue 1 85-93, Copyright © 1993 by American Society of Plant Biologists
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ENVIRONMENTAL AND STRESS PHYSIOLOGY |
Aluminum Effects on Calcium (45Ca2+) Translocation in Aluminum-Tolerant and Aluminum-Sensitive Wheat (Triticum aestivum L.) Cultivars (Differential Responses of the Root Apex versus Mature Root Regions)
J. W. Huang, D. L. Grunes and L. V. Kochian
Department of Soil, Crop, and Atmospheric Sciences, Cornell University (J.W.H.), and United States Plant, Soil, and Nutrition Laboratory, United States Department of Agriculture-Agricultural Research Service, Cornell University, Ithaca, New York 14853 (D.L.G., L.V.K.)
The influence of Al exposure on long-distance Ca2+ translocation from
specific root zones (root apex or mature root) to the shoot was studied in
intact seedlings of winter wheat (Triticum aestivum L.) cultivars
(Al-tolerant Atlas 66 and Al-sensitive Scout 66). Seedlings were grown in
100 [mu]M CaCl2 solution (pH 4.5) for 3 d. Subsequently, a divided chamber
technique using 45Ca2+-labeled solutions (100 [mu]M CaCl2 with or without 5
or 20 [mu]M AlCl3, pH 4.5) was used to study Ca2+ translocation from either
the terminal 5 to 10 mm of the root or a 10-mm region of intact root
approximately 50 mm behind the root apex. The Al concentrations used, which
were toxic to Scout 66, caused a significant inhibition of Ca2+
translocation from the apical region of Scout 66 roots. The same Al
exposures had a much smaller effect on root apical Ca2+ translocation in
Atlas 66. When a 10-mm region of the mature root was exposed to 45Ca2+,
smaller genotypic differences in the Al effects effects on Ca2+
translocation were observed, because the degree of Al-induced inhibition of
Ca2+ translocation was less than that at the root apex. Exposure of the
root apex to Al inhibited root elongation by 70 to 99% in Scout 66 but had
a lesser effect (less than 40% inhibition) in Atlas 66. When a mature root
region was exposed to Al, root elongation was not significantly affected in
either cultivar. These results demonstrate that genotypic differences in
Al-induced inhibition of Ca2+ translocation and root growth are localized
primarily in the root apex. The pattern of Ca2+ translocation within the
intact root was mainly basipetal, with most of the absorbed Ca2+
translocated toward the shoot. A small amount of acropetal Ca2+
translocation from the mature root regions to the apex was also observed,
which accounted for less than 5% of the total Ca2+ translocation within the
entire root. Because Ca2+ translocation toward the root apex is limited,
most of the Ca2+ needed for normal cellular function in the apex must be
absorbed from the external solution. Thus, continuous Al disruption of Ca2+
absorption into cells of the root apex could alter Ca2+ nutrition and
homeostasis in these cells and could play a pivotal role in the mechanisms
of Al toxicity in Al-sensitive wheat cultivars.
