Response to zinc deficiency of two rice lines with contrasting tolerance is determined by root growth maintenance and organic acid exudation rates, and not by zinc-transporter activity
Widod, Broadley, MR, Rose, TJ, Frei, M, Pariasca-Tanaka, J, Yoshihashi, T, Thomson, M, Hammond, JP, Aprile, A, Close, TJ, Ismail, AM & Wissuwa, M 2010, 'Response to zinc deficiency of two rice lines with contrasting tolerance is determined by root growth maintenance and organic acid exudation rates, and not by zinc-transporter activity', New Phytologist, vol. 186, no. 2, pp. 400-414.
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• Zinc (Zn)-deﬁcient soils constrain rice (Oryza sativa) production and cause Zn malnutrition. The identiﬁcation of Zn-deﬁciency-tolerant rice lines indicates that breeding might overcome these constraints. Here, we seek to identify processes underlying Zn-deﬁciency tolerance in rice at the physiological and transcriptional levels.
• A Zn-deﬁciency-tolerant line RIL46 acquires Zn more efﬁciently and produces more biomass than its nontolerant maternal line (IR74) at low [Zn]ext under ﬁeld conditions. We tested if this was the result of increased expression of Zn2+ transporters; increased root exudation of deoxymugineic acid (DMA) or low-molecularweight organic acids (LMWOAs); and⁄or increased root production. Experiments were performed in ﬁeld and controlled environment conditions.
• There was little genotypic variation in transcript abundance of Zn-responsive root Zn2+-transporters between the RIL46 and IR74. However, root exudation of DMA and LMWOA was greater in RIL46, coinciding with increased root expression of putative ligand-efﬂux genes. Adventitious root production was maintained in RIL46 at low [Zn]ext, correlating with altered expression of root-speciﬁc auxinresponsive genes.
• Zinc-deﬁciency tolerance in RIL46 is most likely the result of maintenance of root growth, increased efﬂux of Zn ligands, and increased uptake of Zn-ligand complexes at low [Zn]ext; these traits are potential breeding targets.