Cadmium uptake and partitioning in durum wheat during grain filling

Neil S Harris,Gregory J Taylor

doi:10.1186/1471-2229-13-103

Abstract

BackgroundConcentrations of cadmium (Cd) in the grain of many durum wheats (Triticum turgidum subsp. durum) grown in North American prairie soils often exceed international trade standards. Genotypic differences in root-to-shoot translocation of Cd are a major determinant of intraspecific variation in the accumulation of Cd in grain. We tested the extent to which changes in whole-plant Cd accumulation and the distribution of Cd between tissues influences Cd accumulation in grain by measuring Cd accumulation throughout the grain filling period in two near-isogenic lines (NILs) of durum wheat that differ in grain Cd accumulation.ResultsRoots absorbed Cd and transported it to the shoots throughout the grain filling period, but the low- and high-Cd NILs did not differ in whole-plant Cd uptake. Although the majority of Cd accumulation was retained in the roots, the low- and high-Cd NILs differed substantively in root-to-shoot translocation of Cd. At grain maturity, accumulation of Cd in the shoots was 13% (low-Cd NIL) or 37% (high-Cd NIL) of whole-plant Cd accumulation. Accumulation of Cd in all shoot tissue, including grain, was at least 2-fold greater in the high-Cd NIL at all harvests. There was no net remobilization of shoot Cd pools during grain filling. The timing of Cd accumulation in grain was positively correlated with grain biomass accumulation, and the rate of grain filling peaked between 14 and 28 days post-anthesis, when both NILs accumulated 60% of total grain biomass and 61-66% of total grain Cd content.ConclusionsThese results show that genotypic variation in root-to-shoot translocation of Cd controls accumulation of Cd in durum wheat grain. Continued uptake of Cd by roots and the absence of net remobilization of Cd from leaves during grain filling support a direct pathway of Cd transport from roots to grain via xylem-to-phloem transfer in the stem.

Highlights

Concentrations of cadmium (Cd) in the grain of many durum wheats (Triticum turgidum subsp. durum) grown in North American prairie soils often exceed international trade standards
By 7 d post-anthesis (DPA), when less than 5% of final grain Dry weight (DW) had accumulated (Table 3), concentrations of Cd in the grain were already 2-fold greater in the high-Cd near-isogenic lines (NILs). This was true despite the fact that the low- and high-Cd NILs did not differ in whole-plant Cd uptake (Figure 1), indicating no significant difference in absorption of Cd by roots
The second observation is related to the fact that lowand high-Cd NILs differ in root-to-shoot Cd translocation, and in Cd transport from the flag leaf to the grain, which we have previously shown to be approximately 2-fold greater in the high-Cd NIL [37]

Summary

Introduction

Concentrations of cadmium (Cd) in the grain of many durum wheats (Triticum turgidum subsp. durum) grown in North American prairie soils often exceed international trade standards. Concentrations of cadmium (Cd) in the grain of many durum wheats Durum) grown in North American prairie soils often exceed international trade standards. Genotypic differences in root-to-shoot translocation of Cd are a major determinant of intraspecific variation in the accumulation of Cd in grain. We tested the extent to which changes in whole-plant Cd accumulation and the distribution of Cd between tissues influences Cd accumulation in grain by measuring Cd accumulation throughout the grain filling period in two near-isogenic lines (NILs) of durum wheat that differ in grain Cd accumulation. Cadmium (Cd) is a toxic, non-essential element that is naturally present in most soils. Cadmium is readily absorbed by roots and transported to above ground portions, including grains [1,2]. Some cereals, including rice (Oryza sativa L.) and durum wheat Durum (Desf.) Husn.), can accumulate Cd in grain to levels that exceed international trade standards.

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