AOBPreview originally published online on May 30, 2009
Annals of Botany 2009 104(2):235-241; doi:10.1093/aob/mcp123
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Disorganized distribution of homogalacturonan epitopes in cell walls as one possible mechanism for aluminium-induced root growth inhibition in maize
1 Ministry of Education Key Laboratory for Environmental Remediation and Ecosystem Health, College of Environmental and Resource Sciences, Zhejiang University, Hangzhou 310029, China
2 State Key Laboratory of Plant Physiology and Biochemistry, College of Life Sciences, Zhejiang University, Hangzhou 310058, China
* For correspondence. E-mail sjzheng{at}zju.edu.cn
Received: 20 February 2009 Returned for revision: 1 April 2009 Accepted: 14 April 2009 Published electronically: 30 May 2009
Background and Aims: Aluminium (Al) toxicity is one of the most severe limitations to crop production in acid soils. Inhibition of root elongation is the primary symptom of Al toxicity. However, the underlying basis of the process is unclear. Considering the multiple physiological and biochemical functions of pectin in plants, possible involvement of homogalacturonan (HG), one of the pectic polysaccharide domains, was examined in connection with root growth inhibition induced by Al.
Methods: An immunolabelling technique with antibodies specific to HG epitopes (JIM5, unesterified residues flanked by methylesterifed residues; JIM7, methyl-esterified residues flanked by unesterified residues) was used to visualize the distribution of different types of HG in cell walls of root apices of two maize cultivars differing in Al resistance.
Key Results: In the absence of Al, the JIM5 epitope was present around the cell wall with higher fluorescence intensity at cell corners lining the intercellular spaces, and the JIM7 epitope was present throughout the cell wall. However, treatment with 50 µM Al for 3 h produced 10 % root growth inhibition in both cultivars and caused the disappearance of fluorescence in the middle lamella of both epitopes. Prolonged Al treatment (24 h) with 50 % root growth inhibition in ‘B73’, an Al-sensitive cultivar, resulted in faint and irregular distribution of both epitopes. In ‘Nongda3138’, an Al-resistant cultivar, the distribution of HG epitopes was also restricted to the lining of intercellular spaces when a 50 % inhibition to root growth was induced by Al (100 µM Al, 9 h). Altered distribution of both epitopes was also observed when of roots were exposed to 50 µM LaCl3 for 24 h, resulting in 40 % inhibition of root growth.
Conclusions: Changes in HG distribution and root growth inhibition were highly correlated, indicating that Al-induced perturbed distribution of HG epitopes is possibly involved in Al-induced inhibition of root growth in maize.
Key words: Al toxicity, cell wall, homogalacturnonan, immunofluorescence, methylesterification, pectin
These two authors contributed equally to this work.