Abstract
Nitrogen utilization in higher plants is regulated by many genes at several steps. Toward identification regulatory genes involved in NH4+ uptake, assimilation and subsequent metabolism, chromosome segment substituted lines (CSSLs) developed between Koshihikari (japonica rice) and Kasalath (indica rice) were employed to detect QTLs of root elongation under various concentrations of NH4+. Germinated seedlings were hydroponically grown in an outdoor-growth chamber supplied with 5, 50 or 500 μM NH4+ for a week, and then maximum length of roots were determined. A probability of 0.01 (t-test) was used as the threshold for the detection of QTL. The root length of Kasalath was longer than that of Koshihikari under these NH4+ applications. Many QTLs were detected for root elongation under various concentrations of NH4+ on all chromosomes, except chromosome 3 and 10. In particular, Kasalath allele on QTL of chromosome 6 greatly promoted the root elongation. High-resolution mapping is now in progress.
