Disorganized distribution of homogalacturonan epitopes in cell walls as one possible mechanism for aluminium-induced root growth inhibition in maize.
OBJECTIVE
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.


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 microm 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 microm Al, 9 h). Altered distribution of both epitopes was also observed when of roots were exposed to 50 microm LaCl(3) 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.
Li
Ya Ying
YY
Ministry of Education Key Laboratory for Environmental Remediation and Ecosystem Health, College of Environmental and Resource Sciences, Zhejiang University, Hangzhou, China.
Yang
Jian Li
JL
Zhang
Yue Jiao
YJ
Zheng
Shao Jian
SJ
D000535:Aluminum / Q000633:toxicity*; D002473:Cell Wall / Q000378:metabolism*; D000939:Epitopes / Q000378:metabolism*; D066298:In Vitro Techniques; D018613:Microscopy, Confocal; D010368:Pectins / Q000378:metabolism*; D018517:Plant Roots / Q000187:drug effects* / Q000254:growth & development / Q000378:metabolism; D012989:Soil Pollutants / Q000633:toxicity*; D003313:Zea mays / Q000187:drug effects* / Q000254:growth & development / Q000378:metabolism
D000939:Epitopes; D012989:Soil Pollutants; D010368:Pectins; D000535:Aluminum; C003181:polygalacturonic acid