Seed treatment with growth regulators and crop productivity. I. 2,4-D as an inducer of salinity-tolerance in wheat (Triticum aestivum L.) |
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Authors: | Gulnaz A Iqbal J Farooq S Azam F |
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Institution: | 1. Nuclear Institute for Agriculture and Biology, Faisalabad, Pakistan FAX No 2. Department of Botany, University of the Punjab, Lahore, Pakistan
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Abstract: | The paper investigates how the apoplastic route of ion transfer is affected by the outermost cortex cell layers of a primary
root. Staining of hand-made cross sections with aniline blue in combination with berberine sulfate demonstrated the presence
of casparian bands in the endo- and exodermis, potentially being responsible for hindering apoplastic ion movement. The use
of the apoplastic dye Evan's Blue allowed viewing under a light microscope of potential sites of uncontrolled solute entry
into the apoplast of the root cortex which mainly consisted of injured rhizodermis and/or exodermis cells. The distribution
of the dye after staining was highly comparable to EDX analyses on freeze-dried cryosectioned roots. Here, we used Rb+ as
a tracer for K+ in a short-time application on selected regions of intact roots from intact plants. After subsequent quench-freezing
with liquid propane the distribution of K+ and Rb+ in cell walls was detected on freeze-dried cryosections by their specific
X-rays resulting from the incident electrons in a SEM. All such attempts led to a single conclusion, namely, that the walls
of the two outermost living cell sheaths of the cortex largely restrict passive solute movements into the apoplast. The ring
of turgescent living rhizodermis cells in the root tip region forms the first barrier. With increasing distance to the root
tip, in the course of their maturation resp. degradation, this particular function of the rhizodermis cells is replaced by
the hypodermis resp. exodermis. Furthermore, the restriction of apoplastic ion flow by the outermost cortex cell layers is
rather effective but not complete. Thus, the solute transfer into the stele is mainly restricted by the casparian bands of
the endodermis. The overall conclusion is that the resistances of the rhizodermis and exodermis are additive to the endodermis
in their role of regulating the apoplastic solute movement across roots.
This revised version was published online in August 2006 with corrections to the Cover Date. |
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Keywords: | Cryosectioning endodermis ion localisation ion transport rhizodermis X-ray microanalysis |
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