Germanium is taken up by plant roots by the same route as silicon and causes brown lesions on rice leaves, which plant geneticists use as a marker for silicon and arsenite transport. This study dosed rice seedlings hydroponically with germanic acid and mapped loci linked to lesion severity in a biparental population and a 341-cultivar diversity panel. Leaf germanium accumulation differed about twofold among 19 cultivars and was only weakly related to lesion severity.
Key numbers
- Lesions appeared in the cultivar Bala at 1.5 µM germanic acid, while Azucena showed none at 1.5 or 5 µM; mean lesion cover reached 97% at 500 µM after one week (pp. 5 to 6, Fig 1A).
- At 15 µM germanic acid on day 4, Azucena and Bala had mean lesion cover of 15% and 86% (p. 6).
- Broad-sense heritability of lesion traits in the recombinant inbred lines ranged from 75.8% to 86.1% (p. 6).
- Across 19 cultivars, leaf germanium accumulation varied about twofold (p < 0.001) and was positively related to lesion cover, R2 = 22.8%, P = 0.022 (pp. 9 and 11, Fig 4). Tissue concentrations are shown only in a figure; the text mentions two cultivars at about 12 mg/g, a unit printed as such and not verified (p. 11).
Methods (brief)
Seedlings were grown in half-strength nutrient solution and exposed to germanic acid prepared from germanium dioxide (15 µM for mapping). Lesions were scored as percentage of shoot area. QTL mapping used composite interval mapping; association mapping used 44,100 SNPs with a mixed model. For 19 cultivars, dried shoot tissue was microwave-digested in nitric acid and hydrogen peroxide and analyzed for total germanium by ICP-MS with certified reference material and blanks (p. 5).
Evidence fitness
The paper supports statements that rice takes up germanium through silicon-type transport, that seedlings develop dose-related leaf lesions, and that cultivars differ in germanium accumulation and sensitivity. It does not support any statement on germanium in rice grain, field soils, or the diet, because all exposures were experimental hydroponic doses in seedlings.
Limitations
Hydroponic seedling exposures over days, not field-grown grain. Tissue concentrations are presented graphically, and the one numeric mention in the text carries a unit (mg/g) that could not be checked against a table. Germanium was used mainly as a tracer for silicon and arsenite transport, not studied as a food contaminant.
Related evidence
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