Variation in root growth and hematoxylin staining in response to aluminum stress in cultivated and wild rice.
Jason Londo, Washington University, One Brookings Drive, St. Louis, MO 63130
Understanding stress adaptation in different environments is a fundamental question in plant physiology and plant evolutionary biology. Moreover, it is vital for improving crops on poor soils. Acid-aluminum soils cover 40% of the world’s arable land and the major limiting factor affecting crop success on these soils is aluminum stress. Both cultivated rice, Oryza sativa, and its wild ancestor, Oryza rufipogon grow in acid-aluminum soils of Southeast Asia and are an excellent system for evaluating aluminum resistance in this vital crop. The aim of this study was to examine the natural physiological variation of cultivated and wild rice in response to aluminum stress. Sampling of rice included 86 distinct populations of rice representing 30 cultivated indica varieties, 25 cultivated japonica varieties, and 31 wild rice accessions. Plants were evaluated as seedlings in a completely hydroponic media system and examined at an aluminum stress of 30uM active aluminum. Root measurements were taken and relative root growth rate (RRGR) was used to evaluate the resistance of the root tip to free aluminum in solution. Hematoxylin staining was used to examine the degree of root bound aluminum. Results indicate a wide range in aluminum resistance ability for RRGR and hematoxylin staining within all three rice categories. When examining the RRGR trait, reduced levels of bound aluminum correlate with root growth ability in cultivated rice. However, there are clear differences between the three groups. Cultivated japonica rice is more resistant to aluminum stress than indica rice. Additionally, the aluminum resistance range of wild rice encompasses both cultivated rice ranges, demonstrating the wide natural variation present in the wild ancestor. Finally, correlation of root staining and root growth ability is absent when examining wild rice, suggesting that the domestication of rice has lead to two separate resistance ranges for indica and japonica rice.