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Plant function and evolutionary biology
RESEARCH ARTICLE

Insights into the functional relationship between cytokinin-induced root system phenotypes and nitrate uptake in Brassica napus

Qianqian Guo A , Jonathan Love A , Jiancheng Song B , Jessica Roche A , Matthew H. Turnbull A and Paula E. Jameson A C
+ Author Affiliations
- Author Affiliations

A School of Biological Sciences, University of Canterbury, Private Bag 4800, Christchurch, New Zealand.

B School of Life Sciences, Yantai University, 30 Qingquan Road, Yantai 264005, China.

C Corresponding author. Email: paula.jameson@canterbury.ac.nz

Functional Plant Biology 44(8) 832-844 https://doi.org/10.1071/FP16435
Submitted: 16 December 2016  Accepted: 27 May 2017   Published: 29 June 2017

Abstract

Root system architecture is the spatial arrangement of roots that impacts the capacity of plants to access nutrients and water. We employed pharmacologically generated morphological and molecular phenotypes and used in situ 15N isotope labelling, to investigate whether contrasting root traits are of functional interest in relation to nitrate acquisition. Brassica napus L. were grown in solidified phytogel culture media containing 1 mM KNO3 and treated with the cytokinin, 6-benzylaminopurine, the cytokinin antagonist, PI-55, or both in combination. The pharmacological treatments inhibited root elongation relative to the control. The contrasting root traits induced by PI-55 and 6-benzylaminopurine were strongly related to 15N uptake rate. Large root proliferation led to greater 15N cumulative uptake rather than greater 15N uptake efficiency per unit root length, due to a systemic response in the plant. This relationship was associated with changes in C and N resource distribution between the shoot and root, and in expression of BnNRT2.1, a nitrate transporter. The root : shoot biomass ratio was positively correlated with 15N cumulative uptake, suggesting the functional utility of root investment for nutrient acquisition. These results demonstrate that root proliferation in response to external nitrate is a behaviour which integrates local N availability and the systemic N status of the plant.

Additional keywords: NO3, N uptake, PI-55, root system architecture (RSA).


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