An analytical microscopical study on the role of the exodermis in apoplastic Rb+(K+) transport in barley roots

被引:25
作者
Gierth M. [1 ]
Stelzer R. [1 ]
Lehmann H. [1 ]
机构
[1] Inst. F. Tierokologie Zellbiologie, Tierarztl. Hochschule Hannover, D-30559 Hannover
关键词
Cryosectioning; Endodermis; Ion localisation; Ion transport; Rhizodermis; X-ray microanalysis;
D O I
10.1023/A:1004437516331
中图分类号
学科分类号
摘要
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.
引用
收藏
页码:209 / 218
页数:9
相关论文
共 33 条
[1]  
Aikman D.P., Harmer R., Rust T.S.O., Electrical resistance and ion movement through excised discs of sugar beet root tissue, Physiol. Plant., 48, pp. 395-402, (1980)
[2]  
Bayliss C., Van Der Weele C., Canny M.J., Determinations of dye diffusivities in the cell-wall apoplast of roots by a rapid method, New Phytol., 134, pp. 1-4, (1996)
[3]  
Brundrett M.C., Enstone D.E., Peterson C.A., A berberine-aniline blue staining procedure for suberin, lignin, and callose in plant tissue, Protoplasma, 146, pp. 133-142, (1988)
[4]  
Clarkson D.T., Root structure and sites of ion uptake, Plant Roots. The Hidden Half. 2nd Edition, Revised and Expanded, pp. 483-503, (1996)
[5]  
Cruz R.T., Jordan W.R., Drew M.C., Structural changes and associated reduction of hydraulic conductance in roots of Sorghum bicolor L. following exposure to water deficit, Plant Physiol., 99, pp. 203-212, (1992)
[6]  
Damus M., Peterson R.L., Enstone D.E., Peterson C.A., Modification of cortical cell walls in roots of seedless vascular plants, Bot. Acta, 110, pp. 190-195, (1997)
[7]  
Echlin P., Low Temperature Microscopy and Analysis, (1992)
[8]  
Enstone D.E., Peterson C.A., The apoplastic permeability of corn root apices, Can. J. Bot., 70, pp. 1502-1512, (1992)
[9]  
Esau K., Pflanzenanatomie, pp. 353-395, (1969)
[10]  
Frey B., Brunner I., Walther P., Scheidegger C., Zierold K., Element localisation in ultrathin cryosections of high pressure frozen ectomycorrhizal roots, Plant Cell Environ., 20, pp. 929-937, (1997)