*4.7. Permeability Test*

Adventitious roots (115–120 mm length) were cut at the root–shoot junction. The permeabilities of the exodermal layers at the basal parts (95–105 mm from the root apex), middle parts (35–45 mm from the root apex), and root tips (2.5–7.5 mm from the root apex) were assessed with an apoplastic tracer, periodic acid, as described previously [13]. Periodic acid that penetrated the root tissue was visualized as a purple color under white light with the above microscope and camera.

### *4.8. Statistical Analysis*

Means of aerenchyma formation (% aerenchyma/cortex) were compared with one-way analysis of variance (ANOVA) and Tukey's honest significant difference (HSD) for multiple comparisons at the 5% probability level or with a two-sample *t*-test at the 5% probability level. Means of fluorescence intensities of Fluorol Yellow 088 or Basic Fuchsin between accession W2165 of *O. glumaepatula* and cv. Nipponbare was compared with a two-sample *t*-test at the 5% probability level. The data were analyzed with R version 3.5.1 [55].

**Supplementary Materials:** The following are available online at http://www.mdpi.com/2223-7747/9/7/880/s1, Figure S1: Procedure for quantifying Fluorol Yellow 088 fluorescence intensity; Figure S2: Procedure for quantifying Basic Fuchsin fluorescence intensity.

**Author Contributions:** M.E. and K.S. designed the experiments. M.E. and Y.S. performed the experiments and analyses. K.S. supervised the experiments. M.E. and K.S. wrote the article. All authors have read and agreed to the published version of the manuscript.

**Funding:** This work was supported by the Japan Society for the Promotion of Science (Grant No. JP16KK0173, JP17K15211, JP19K05978).

**Acknowledgments:** We thank Takeshi Fukao for stimulating discussions. The wild rice accessions used in the present study were distributed from the National Institute of Genetics supported by the National Bioresource Project (NBRP), AMED, Japan.

**Conflicts of Interest:** The authors declare no conflict of interest.

#### **References**


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