Isolation and characterization of a short lateral root mutant in rice (Oryza sativa L.)

Proper initiation and elongation of lateral roots are the important factors that determine the architecture of plant roots. However, little is known about the mechanisms controlling lateral root elongation. In an effort to understand the mechanisms of lateral root elongation in rice, a monogenic recessive mutant, aff1 (altered lateral root formation) has been isolated from tissue culture-derived R, lines. The striking phenotype of the mutant was its significantly shorter lateral roots as compared with wild type. The mutation also caused hyper proliferation of lateral roots. Besides the defect in lateral root formation, the mutant also displayed reduction in both the number and length of root hairs. These defects were found not only on seminal root but also on crown roots of both early and adult stages. The mutation also affected seminal and crown root elongation at early growth stage. The mutant exhibited more resistance response to exogenous IBA and ABA and auxin transport inhibitors 1-naphthylphthalamic acid (NPA) and 2,3,5-triiodobenzoic acid (TIBA), but did not show resistance to indole-3-acetic acid (IAA), NAA or 2,4-D. Exogenous application of IBA promoted lateral root elongation in the mutant to the extent comparable to that of untreated wild type. Exogenously applied IBA, IAA, NAA and 2,4-D rescued successfully the defects in root hair formation in the mutant. These results suggest that the processes of lateral root elongation and root hair formation in rice are regulated by auxin and that the defects in this mutant might be related to altered auxin response or transport in which IBA is playing an important role. (C) 2003 Elsevier Ireland Ltd. All rights reserved.