Abstract
Grain amaranth (Amaranthus hypochondriacus L.) is abundant in oxalate and can secrete oxalate under aluminium (Al) stress. However, the features of Al-induced secretion of organic acid anions (OA) and potential genes responsible for OA secretion are poorly understood. Here, Al-induced OA secretion in grain amaranth roots was characterized by ion charomatography and enzymology methods, and suppression subtractive hybridization (SSH) together with quantitative real-time PCR (qRT-PCR) was used to identify up-regulated genes that are potentially involved in OA secretion. The results showed that grain amaranth roots secrete both oxalate and citrate in response to Al stress. The secretion pattern, however, differs between oxalate and citrate. Neither lanthanum chloride (La) nor cadmium chloride (Cd) induced OA secretion. A total of 84 genes were identified as up-regulated by Al, in which six genes were considered as being potentially involved in OA secretion. The expression pattern of a gene belonging to multidrug and toxic compound extrusion (MATE) family, AhMATE1, was in close agreement with that of citrate secretion. The expression of a gene encoding tonoplast dicarboxylate transporter and four genes encoding ATP-binding cassette transporters was differentially regulated by Al stress, but the expression pattern was not correlated well with that of oxalate secretion. Our results not only reveal the secretion pattern of oxalate and citrate from grain amaranth roots under Al stress, but also provide some genetic information that will be useful for further characterization of genes involved in Al toxicity and tolerance mechanisms.
Highlights
Aluminium (Al) toxicity is one of the major constraints for crop production in acid soils, which occupies approximately 50% of potentially arable lands worldwide [1]
The results showed that grain amaranth roots secrete both oxalate and citrate into rhizosphere under Al stress, but secretion pattern differed between oxalate and citrate
We have previously demonstrated that some oxalate accumulators can secrete oxalate from their roots in response to Al stress [22]
Summary
Aluminium (Al) toxicity is one of the major constraints for crop production in acid soils, which occupies approximately 50% of potentially arable lands worldwide [1]. A number of possible mechanisms responsible for the Al-induced inhibition of root elongation have been proposed. Al may alter cytoskeletal structure, interfere with DNA replication, disrupt signal transduction pathways, and trigger oxidative stress response [3,4,5]. Transcriptional analysis revealed that hundreds to thousands of genes were up- and down-regulated within several hours of exposure to Al stress, which are involved in a variety of physiological and molecular processes [6,7,8,9,10]. The inhibition of root elongation appears to be a toxic syndrome that results from disorder of a series of physiological and biochemical processes
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