The role of organic acids in the short- and long-term aluminum tolerance in maize seedlings (<Emphasis Type="Italic">Zea mays</Emphasis> L.) |
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Authors: | Radhouane Chaffai Brahim Marzouk |
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Institution: | (1) Present address: Department of Biological Sciences, BMG Macromolecular Biochemistry and Genetics Research Unit, Faculty of Sciences of Gafsa, University of Gafsa, Zarroug, 2112 Gafsa, Tunisia;(2) Aromatic and Medicinal Plants Research Unit, Biotechnology Center, Borj Cedria Technopark, BP 901, 2050 Hammam-Lif, Tunisia |
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Abstract: | Aluminum (Al) affects numerous physiological processes in plants. However, Al tolerance mechanisms mediated by increased synthesis
of organic acids (OAs) have been outlined recently. In this study, we examined the role of OAs in the short (1–8 h) and long-term
(4 days) Al tolerance in maize seedlings. Exposure to Al stress for 4 days results in a rapid inhibition of root growth. Al
induced morphological changes in the maize roots, especially at a higher solution of Al concentration (1,000 μM Al). The increase
in Al accumulation in roots, including strongly elevated levels of Al accumulated in root cell walls suggests that Al tolerance
in maize is mediated in part by higher accumulation of Al in the roots. The enhanced citrate exudation, which was only observed
at 1,000 μM Al may lead to detoxification of Al by formation of OA–Al complexes in the root apoplast. This mechanism has been
suggested to play a significant role in Al resistance response in maize. The short-term responses underlying internal detoxification
via OA-chelators were also investigated. Succinate, malate, citrate and total root OA contents decreased markedly, 2 h after
the Al exposure. At 4 and 8 h time points, OA contents increased or remained unchanged, except for that of malate which decreased.
The level of OAs in shoots, on the other hand, showed alterations that were less pronounced in response to Al. Specifically,
the citrate and total OA concentrations significantly increased at 4 h, but showed a pronounced decrease at the 8 h time point.
Based on our findings, we propose that multiple responses, including Al exclusion by Al accumulation in root cells and citrate
efflux, may contribute towards higher Al resistance in maize. The rapid OA changes in responses to short-term Al treatment
may not be responsible for Al tolerance. However, increased OA synthesis observed in this study may be involved in diminishing
the stress triggered by Al. The molecular aspects underlying Al resistance mechanism via Al-induced expression of the enzymes
catalyzing OA synthesis and metabolism remain to be elucidated. |
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Keywords: | Aluminum Long-term effects Organic acids Short-term effects Zea mays L |
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