Interactions between light intensity and phosphorus nutrition affect the phosphate-mining capacity of white lupin (Lupinus albus L.).

Lingyun Cheng,Fusuo Zhang,Carroll P Vance,Philip J White,Xiaoyan Tang,Jianbo Shen

doi:10.1093/jxb/eru135

Abstract

Light intensity affects photosynthetic carbon (C) fixation and the supply of carbon to roots. To evaluate interactions between carbon supply and phosphorus (P) supply, effects of light intensity on sucrose accumulation, root growth, cluster root formation, carboxylate exudation, and P uptake capacity were studied in white lupin (Lupinus albus L.) grown hydroponically with either 200 µmol m(-2) s(-1) or 600 µmol m(-2) s(-1) light and a sufficient (50 µM P) or deficient (1 µM P) P supply. Plant biomass and root:shoot ratio increased with increasing light intensity, particularly when plants were supplied with sufficient P. Both low P supply and increasing light intensity increased the production of cluster roots and citrate exudation. Transcripts of a phosphoenol pyruvate carboxylase gene (LaPEPC3) in cluster roots (which is related to the exudation of citrate), transcripts of a phosphate transporter gene (LaPT1), and P uptake all increased with increasing light intensity, under both P-sufficient and P-deficient conditions. Across all four experimental treatments, increased cluster root formation and carboxylate exudation were associated with lower P concentration in the shoot and greater sucrose concentration in the roots. It is suggested that C in excess of shoot growth capabilities is translocated to the roots as sucrose, which serves as both a nutritional signal and a C-substrate for carboxylate exudation and cluster root formation.

Highlights

Cluster roots are dense clusters of rootlets with determinate growth that form on lateral roots of many species of Proteaceae and several species in other plant families (Dinkelaker et al, 1995; Skene, 1998; Lamont, 2003; Lambers et al, 2011)
The root:shoot dry weight ratio was greater in plants grown under high light intensity, but this effect was only significant in the P-sufficient plants, in which increasing light intensity from 200 to 600 μmol m–2 s–1 almost doubled root:shoot dry weight ratio (Fig. 1C)
This study was conducted to determine whether greater photosynthesis manipulated by light intensity, and plant P status manipulated by P supply to roots affect cluster root formation and function

Summary

Introduction

Cluster roots are dense clusters of rootlets with determinate growth that form on lateral roots of many species of Proteaceae and several species in other plant families (Dinkelaker et al, 1995; Skene, 1998; Lamont, 2003; Lambers et al, 2011). The special morphology of cluster roots increases root surface area for P uptake and this is combined with the release of large amounts of P-mobilizing root exudates (mainly citrate and malate, and others, such as flavonoids) into the rhizosphere of P-deficient plants (Dinkelaker et al, 1989; Keerthisinghe et al, 1998; Neumann and Martinoia, 2002; Lambers et al, 2006; Weisskopf et al, 2006).

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