Linear energy transfer (LET) is an important parameter for ion beam mutagenesis. We irradiated rice seeds with carbon ions (LET: 23, 30, 50, or 57 keV µm 1 ), neon ions (LET: 63 or 70 keV µm 1 ), or argon ions (LET: 290 keV µm 1 ). We subsequently isolated 56 mutants and analyzed the mutations in the responsible genes for mutant phenotypes to evaluate the effects of different LETs in rice. Mutations were classified as single nucleotide variants, small deletions (<100 bp), large deletions (≥100 bp), and chromosomal rearrangements (inversions and translocations). The carbon and neon ions (23-70 keV µm 1 ) tended to induce small deletions, whereas the argon ions mainly induced large deletions. These results were consistent with the findings of our previous studies on Arabidopsis mutants irradiated with carbon ions (23 or 30 keV µm 1 ) or argon ions (290 keV µm 1 ). Moreover, the deletions caused by argon ions were larger than those induced by carbon or neon ions. Therefore, in rice and Arabidopsis, carbon ion (23 or 30 keV µm 1 ) irradiations are more likely to induce single-gene mutations, whereas irradiation with argon ions (290 keV µm 1 ) tends to cause large deletions, that can be useful to disrupt tandemly arrayed genes.
Saponins are secondary metabolites that are widely distributed in plants. There are two major saponin precursors in soybean: soyasapogenol A, contributing to the undesirable taste, and soyasapogenol B, some of which have health benefits. It is important to control the ratio and content of the two major saponin groups to enhance the appeal of soybean as a health food. The structural diversity of saponin in the sugar chain composition makes it hard to quantify the saponin content. We measured the saponin content in soybean by removing the sugar chain from the saponin using acidic hydrolysis and detected novel quantitative trait loci (QTLs) for saponin content. Major QTLs in the hypocotyl were identified on chromosome 5 near the SSR marker, Satt 384, while those in the cotyledon were on chromosome 6 near Sat_312, which is linked to the T and E1 loci. Our results suggest that saponin contents in the hypocotyl and cotyledon are controlled by different genes and that it is difficult to increase the beneficial group B saponin and to decrease the undesirable group A saponin at the same time.
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