Apoplastic pH and FeIII reduction in young sunflower (Helianthus annuus) roots

被引:28
作者
Kosegarten, H
Hoffmann, B
Rroco, E
Grolig, F
Glüsenkamp, KH
Mengel, K
机构
[1] Univ Giessen, Inst Plant Nutr, D-35390 Giessen, Germany
[2] Univ Giessen, Interdisciplinary Res Ctr, D-35392 Giessen, Germany
[3] Agr Univ Tirana, Dept Agron, Kamez, Tirana, Albania
[4] Univ Marburg, Fac Biol Bot, D-35032 Marburg, Germany
[5] Squarix GmbH, D-45768 Marl, Germany
关键词
D O I
10.1111/j.1399-3054.2004.00377.x
中图分类号
Q94 [植物学];
学科分类号
071001 ;
摘要
The relationship between the apoplastic pH in young sunflower roots (Helianthus annuus L.) and the plasmalemma ferric chelate reductase (FC-R; EC 1.16.1.7) activity in roots was investigated. The hypothesis was tested that a high apoplastic pH depresses FC-R activity, thereby restricting the uptake of Fe2+ into the cytosol. Until recently, little has been known about this relationship, because pH and redox reaction measurements are difficult to perform within the confines of the root apoplast. We recorded the apoplastic pH by means of the fluorescence ratio in conjunction with video microscopy by covalently tagging fluorescein boronic acid to OH groups of the root cell wall. Fe-III reduction was measured using a similar approach by tagging ferrozine diboronic acid with OH groups of the cell wall. Ferrozine forms an Fe2+ complex, thus indicating the reduction of ferric iron. In roots bathing in buffered outer solutions of different pH, a high pH sensitivity of apoplastic Fe-III reduction was found, with the highest ferric iron reduction rates at an apoplastic pH of 4.9; above an apoplastic pH of 5.3, no reduction was observed. Nitrate in the bathing solution increased the apoplastic pH and hence depressed the Fe-III reduction; ammonium had the reverse effect. Nitrate together with HCO3-, a combination which is typical of calcareous soils, had the strongest depressing effect. From the results, it can be concluded that the main reason for the frequently occurring iron deficiency chlorosis of plants grown on calcareous soils is the inhibition of Fe-III reduction in the apoplast, and hence Fe2+ uptake into the cytosol.
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页码:95 / 106
页数:12
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