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Phloem Transport Of Arsenic Species From Flag Leaf To Grain During Grain Filling
Citation:
Carey, A., G. J. Norton, C. Deacon, K. G. SCHECKEL, E. Lombi, T. Punshon, M. Guerinot, A. Lanzirotti, M. Newville, Y. Choi, A. H. Price, AND A. A. Meharg. Phloem Transport Of Arsenic Species From Flag Leaf To Grain During Grain Filling. I. Woodward (ed.), New Phytologist. Wiley-Blackwell Publishing, Hoboken, NJ, 192(1):87-98, (2011).
Impact/Purpose:
To investigate the retranslocation of As species from flag leaves into the filling rice grain, by feeding As species directly into the flag leaves during grain fill, and to determine the spatial unloading of key As species within the developing rice grain and establish whether differences existed between leaf-retranslocated and direct stem-transported As. To investigate the role of silicic acid and arsenite pathways, germanic acid, a silicic acid analog, was used as a tracer in competitive inhibition in shoot and stem feeding studies.
Description:
Strategies to reduce arsenic (As) in rice grain, below concentrations that represent a serious human health concern, require that the mechanisms of As accumulation within grain be established. Therefore, retranslocation of As species from flag leaves into filling rice grain was investigated. Arsenic species were delivered through cut flag leaves during grain fill. Spatial unloading within grains was investigated using synchrotron X-ray fluorescence (SXRF) microtomography. Additionally, the effect of germanic acid (a silicic acid analog) on grain As accumulation in arsenite-treated panicles was examined. Dimethylarsinic acid (DMA) and monomethylarsonic acid (MMA) were extremely efficiently retranslocated from flag leaves to rice grain; arsenate was poorly retranslocated, and was rapidly reduced to arsenite within flag leaves; arsenite displayed no retranslocation. Within grains, DMA rapidly dispersed while MMA and inorganic As remained close to the entry point. Germanic acid addition did not affect grain As in arsenite-treated panicles. Three-dimensional SXRF microtomography gave further information on arsenite localization in the ovular vascular trace (OVT) of rice grains. These results demonstrate that inorganic As is poorly remobilized, while organic species are readily remobilized from leaves to grain. Stem translocation of inorganic As may not rely solely on silicic acid transporters.
