Assessing the contributions of lateral roots to element uptake in rice using an auxin-related lateral root mutant

Background and aims
The role of lateral roots in the acquisition of nutrients and contaminants from the soil may vary between mobile and immobile solutes. The aim of the present study was to quantify the contributions of lateral roots to growth and elemental uptake under different conditions.

Methods
A lateral rootless mutant of rice (Oryza sativa) with a gain-of-function mutation in OsIAA11 was compared with its wild-type (WT) in hydroponic, pot and field conditions. Three soils varying in the P availability were used in the pot experiment. Synchrotron fast X-ray fluorescence (XRF) was used to map the distribution of trace elements in fresh hydrated roots.

Results
The Osiaa11 mutant grew smaller compared with the WT in all three experiments, especially in the field. The difference was larger in a P-sufficient soil than in P-deficient soils in the pot experiment. Elemental concentrations in the roots and shoots were affected differently by the mutation, depending on the elements and the growth media. The apparent contributions of lateral roots to elemental uptake varied from 2.7 to 82.5% in the hydroponic experiment, from −19.8 to 76.4% in the pot experiment, and from 30 to 76% in the field experiment. In general, the apparent contributions to the uptake of P, Mn, Zn, Cu and As were larger than that for the biomass, whereas for N, S and K the apparent contributions were smaller than or similar to the effect on plant biomass. Synchrotron XRF revealed strong accumulation of Mn, Zn, Cu, As and Se in the lateral roots of the WT.

Conclusions
Lateral roots play an important role in the acquisition of less mobile elements such as P, Mn, Zn, Cu and As, but have relatively small effects on the acquisition of mobile elements such as N, S and K.