The exodermis: a variable apoplastic barrier

被引:277
作者
Hose, E
Clarkson, DT
Steudle, E
Schreiber, L
Hartung, W
机构
[1] Univ Wurzburg, Julius Von Sachs Inst Biowissensch, Lehrstuhl Bot 1, D-97082 Wurzburg, Germany
[2] IACR, Long Ashton Res Stn, Bristol BS18 9AF, Avon, England
[3] Univ Bayreuth, Lehrstuhl Pflanzenokol, D-95440 Bayreuth, Germany
[4] Univ Bonn, Inst Bot, Okophysiol Abt, D-53115 Bonn, Germany
关键词
exodermis; plant roots; barrier; variable resistance; solutes; water;
D O I
10.1093/jexbot/52.365.2245
中图分类号
Q94 [植物学];
学科分类号
071001 ;
摘要
The exodermis (hypodermis with Casparian bands) of plant roots represents a barrier of variable resistance to the radial flow of both water and solutes and may contribute substantially to the overall resistance. The variability is a result largely of changes in structure and anatomy of developing roots. The extent and rate at which apoplastic exodermal barriers (Casparian bands and suberin lamellae) are laid down in radial transverse and tangential walls depends on the response to conditions in a given habitat such as drought, anoxia, salinity, heavy metal or nutrient stresses. As Casparian bands and suberin lamellae form in the exodermis, the permeability to water and solutes is differentially reduced. Apoplastic barriers do not function in an all-or-none fashion. Rather, they exhibit a selectivity pattern which is useful for the plant and provides an adaptive mechanism under given circumstances. This is demonstrated for the apoplastic passage of water which appears to have an unusually high mobility, ions, the apoplastic tracer PTS, and the stress hormone ABA. Results of permeation properties of apoplastic barriers are related to their chemical composition. Depending on the growth regime (e.g. stresses applied) barriers contain aliphatic and aromatic suberin and lignin in different amounts and proportion. It is concluded that, by regulating the extent of apoplastic barriers and their chemical composition, plants can effectively regulate the uptake or loss of water and solutes. Compared with the uptake by root membranes (symplastic and transcellular pathways), which is under metabolic control, this appears to be an additional or compensatory strategy of plants to acquire water and solutes.
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页码:2245 / 2264
页数:20
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