Specific Root Traits are Important for Boron Efficiency in Rapeseed and Arabidopsis Genotypes

Boron (B) is an essential micronutrient for plants. B-deficiency has one of the most drastic inhibitory effects on primary and lateral root growth amongst all nutrient deficiencies. 590 rapeseed cultivars have been screened for B-deficiency tolerance traits at the root level in in vitro and soil conditions. Three highly B-deficiency tolerant cultivars (CR2267, CR2280 and CR2285) have been identified and stand out due to a non-inhibited root growth under B-deficient conditions. Their strikingly short and thick roots respond however to other deficiencies in a nutrient-specific manner. Morphological, histological and physiological B-deficiency root responses have been analysed and will be presented.

B transporters (BORs) and Nodulin26-like Intrinsic Proteins (NIPs) control B transport processes in plants. We cloned 19 BnaNIPs and 6 BnaBOR1s, analysed their metalloid transport properties in heterologous expression systems and determined their specific expression patterns via qPCR. B root uptake capacities were quantified using ICP-MS analysis. These experiments demonstrated that B transporters of B-efficient genotypes contribute significantly to an efficient root B uptake and root-to-shoot translocation. A DH population of a cross between a B-deficiency tolerant and sensitive cultivar is presently being established to identify genes being responsible for the B-deficiency tolerance and the short root phenotype.

Additionally, a root and shoot phenotyping experiment was performed with a set of 188 Arabidopsis accessions in order to identify B-deficiency tolerant genotypes and to identify B-deficiency tolerance mechanism in the root. B-deficiency tolerant Arabidopsis accessions have been identified and analysed for the expression of B transport protein encoding genes, root system architecture traits, and their elemental composition under B-deficient and sufficient conditions. Genome wide association analyses were performed to identify genes which contribute to B-deficiency tolerance mechanisms in roots.

The enormous root growth plasticity of rapeseed and Arabidopsis genotypes grown under B-deficient conditions suggests that different B-efficiency mechanisms must exist.