Abstract
BackgroundPhosphorus (P) deficiency limits crop production worldwide. Crops differ in their ability to acquire and utilise the P available. The aim of this study was to determine root traits (root exudates, root system architecture (RSA), tissue-specific allocation of P, and gene expression in roots) that (a) play a role in P-use efficiency and (b) contribute to large shoot zinc (Zn) concentration in Brassica oleracea.ResultsTwo B. oleracea accessions (var. sabellica C6, a kale, and var. italica F103, a broccoli) were grown in a hydroponic system or in a high-throughput-root phenotyping (HTRP) system where they received Low P (0.025 mM) or High P (0.25 mM) supply for 2 weeks. In hydroponics, root and shoot P and Zn concentrations were measured, root exudates were profiled using both Fourier-Transform-Infrared spectroscopy and gas-chromatography-mass spectrometry and previously published RNAseq data from roots was re-examined. In HTRP experiments, RSA (main and lateral root number and lateral root length) was assessed and the tissue-specific distribution of P was determined using micro-particle-induced-X-ray emission. The C6 accession had greater root and shoot biomass than the F103 accession, but the latter had a larger shoot P concentration than the C6 accession, regardless of the P supply in the hydroponic system. The F103 accession had a larger shoot Zn concentration than the C6 accession in the High P treatment. Although the F103 accession had a larger number of lateral roots, which were also longer than in the C6 accession, the C6 accession released a larger quantity and number of polar compounds than the F103 accession. A larger number of P-responsive genes were found in the Low P treatment in roots of the F103 accession than in roots of the C6 accession. Expression of genes linked with “phosphate starvation” was up-regulated, while those linked with iron homeostasis were down-regulated in the Low P treatment.ConclusionsThe results illustrate large within-species variability in root acclimatory responses to P supply in the composition of root exudates, RSA and gene expression, but not in P distribution in root cross sections, enabling P sufficiency in the two B. oleracea accessions studied.
Highlights
Phosphorus (P) deficiency limits crop production worldwide
The largest root P concentrations were measured in plants receiving High P supply, and the shoot P concentration of the F103 accession receiving a Low P supply did not differ from the shoot P concentration of the C6 accession receiving a High P supply (Fig. 1c, d)
The greatest P efficiency ratio (PER) was found in the C6 accession receiving a Low P supply and the smallest in the F103 accession receiving a High P supply (Fig. 1f)
Summary
Phosphorus (P) deficiency limits crop production worldwide. Crops differ in their ability to acquire and utilise the P available. The most favourable root system architecture (RSA) for P acquisition is a combination of i) large root biomass, root / shoot biomass ratio, cortical aerenchyma, root surface area in the topsoil and in patches of high P phytoavailability, ii) ability to form mycorrhizal symbioses, acidify the rhizosphere, release organic compounds and phosphatases, and iii) greater phosphate (Pi) uptake capacity of root cells [5, 8] In this context, a greater number of lateral roots was found in Brassica oleracea L. accessions with average to high yields at suboptimal P supply and the number of lateral roots increased with yield potential [9]. In Arabidopsis thaliana (L.) Heynh., low P availability promotes the development of a highly branched root system to the detriment of the primary root, characterised by greater production of lateral roots and root hairs [12, 13]
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