PLANT PHYSIOLOGY , Vol 110, Issue 1 217-225, Copyright © 1996 by American Society of Plant Biologists
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WHOLE PLANT, ENVIRONMENTAL, AND STRESS PHYSIOLOGY |
Formation of Root Epidermal Transfer Cells in Plantago
W. Schmidt and M. Bartels
Carl von Ossietzky Universitat Oldenburg, Fachbereich Biologie, 26111 Oldenburg, Postfach 2503, Germany
The root ultrastructure and transmembrane electron transport activities of
two Plantago species have been examined with respect to alterations in
response to Fe deficiency, exogenously supplied auxin, and the presence of
chromium in the external medium. Both species showed increased ferric
reductase activity upon Fe starvation, but they differed in the maximum
rates. The addition of chromium to the nutrient solution led to a further
enhancement in Fe-ethylenediaminetetraacetate reduction by Fe-deficient
plants. In roots of Plantago lanceolata, the enhanced redox activity is
associated with the formation of transfer cells in the epidermis. Similar
characteristics of rhizodermal cells were observed in Fe-sufficient roots 3
d after application of the auxin analog 2,4-dichlorophenoxy-acetic acid. No
structural adaptations occurred in roots of Plantago maritima. A
quantitative estimation of the frequencies of transfer cells in root
segments of Fe-deficient plants that differ in reduction activity revealed
no correlation between the two phenomena. It is concluded that the area of
plasmalemma infoldings is not specialized for the enhanced reduction of
extracytoplasmatic Fe in response to Fe deficiency. The role of transfer
cells in the adaptation to suboptimal Fe availability and the mechanisms
triggering their formation are discussed.
