Brassica napus root mutants insensitive to exogenous cytokinin show phosphorus efficiency.

Background and aims: Cytokinins are known to negatively regulate plant root development and phosphorus (P) starvation responses. In this study, two Brassica napus root mutants insensitive to exogenous cytokinin, prl1 (a mutant with an elongated primary root) and lrn1 (a mutant with more lateral roots), were identified and used to evaluate P efficiency, alongside wild type (WT) plants. Methods: Solution and pot culture, RNA isolation, RT-PCR were used. Results: lrn1 produced the highest shoot dry weight (SDW) and root dry weight (RDW) among the three genotypes at both low P (LP) and high P (HP) conditions. prl1 had higher SDW at both P conditions, and higher RDW at LP, in contrast to WT plants. lrn1 not only accumulated more P from the culture medium but utilized it effectively in shoot growth, whilst prl1 just showed higher P use efficiency compared to WT at LP. Trans-zeatin riboside (tZR) and isopentenyl adenosine (iPA) concentration in lrn1 roots were both significantly lower than that in WT roots at both P conditions. Root iPA concentration in prl1 was lower than that in WT under both P conditions, however, root tZR concentration was greater in prl1 than WT under LP condition. Transcription of the P starvation induced genes BnSPX3;1 and BnSPX3;2 were up-regulated in the roots of mutants under both P conditions. Conclusions: These results suggested that an improved root system might be associated with the reduced cytokinin concentration and lead to a significant increase in acquisition and utilization of P nutrient for lrn1. [ABSTRACT FROM AUTHOR]