Species-Specific Relationship between Transpiration and Cadmium Translocation in Lettuce, Barley and Radish

Mst Fardausi Ahkter,Sheila M Macfie

doi:10.5539/jps.v1n1p2

Abstract

Cadmium (Cd) may accumulate in plants to levels that are of concern in human diets. Our ability to predict the accumulation of Cd in plants is restricted by our poor understanding of the physiological processes that control Cd accumulation and translocation. A hydroponic experiment was carried out to test the hypothesis that the amount of Cd taken up and translocated to aboveground tissues is proportional to the volume of water transpired in lettuce (Lactuca sativa L.), barley (Hordeum vulgare L.) and radish (Raphanus sativus L.). Transpiration was measured as mass of water lost. Increased transpiration caused increased accumulation of Cd in plants; however, the proportion of total Cd translocated to the leaves ranged from 85% in lettuce to 66% in radish to only 21% in barley. Thus, factors controlling species-specific internal distribution of Cd are more important than transpiration in translocating Cd to aboveground tissues.

Highlights

Cadmium (Cd) is a non-essential element for almost all biota with the exception of Thalassiosira weissflogii (Grunow) G
The hypothesis that the amount of Cd taken up and translocated to aboveground tissues is proportional to the total volume of water transpired in lettuce (Lactuca sativa L.), barley (Hordeum vulgare L.) and radish (Raphanus sativus L.) grown in a non-toxic Cd concentration was tested
Lettuce grown in the highest dose of Cd transpired 27% less total water than did plants grown in control solution but transpiration per unit leaf area was 75% higher for plants grown with 2.0 M Cd relative to control plants

Summary

Introduction

Cadmium (Cd) is a non-essential element for almost all biota with the exception of Thalassiosira weissflogii (Grunow) G. The two main sources of Cd in soils are geological parent materials and inputs from anthropogenic sources (Nriagu & Pacyna, 1988). Soils derived from Cd-rich parent materials can have concentrations up to 24 mg total Cd kg-1 (Alloway & Steinnes, 1999). Anthropogenic sources include the application of manure and sewage sludge as well as certain industrial activities. In Canada, Cd-contaminated phosphorus (P) fertilizers are one of the major sources of Cd-contamination in agricultural systems and concentrations of Cd in P fertilizers could be as much as 300 mg Cd kg-1 dry product (Grant & Sheppard, 2008). It is recommended to keep Cd concentrations below regulatory guidelines in vegetables, fruits, grains and other agricultural products to avoid metal toxicity (Canadian Food Inspection Agency [CFIA], 2011). Because the concentration of Cd in edible plant tissues is not always directly proportional to the concentration of Cd in the ISSN 1927-0461 E-ISSN 1927-047X soil (Carbonell et al, 2011; Hejcman et al, 2009; Smolders et al, 2009; Wang et al, 2006), understanding the mechanisms of Cd accumulation and translocation in plants is important to ensuring food safety

Objectives

Methods

Results

Discussion

Conclusion