Cadmium translocation by contractile roots differs from that in regular, non-contractile roots.
OBJECTIVE
Contractile roots are known and studied mainly in connection with the process of shrinkage of their basal parts, which acts to pull the shoot of the plant deeper into the ground. Previous studies have shown that the specific structure of these roots results in more intensive water uptake at the base, which is in contrast to regular root types. The purpose of this study was to find out whether the basal parts of contractile roots are also more active in translocation of cadmium to the shoot.


METHODS
Plants of the South African ornamental species Tritonia gladiolaris were cultivated in vitro for 2 months, at which point they possessed well-developed contractile roots. They were then transferred to Petri dishes with horizontally separated compartments of agar containing 50 µmol Cd(NO3)2 in the region of the root base or the root apex. Seedlings of 4-d-old maize (Zea mays) plants, which do not possess contractile roots, were also transferred to similar Petri dishes. The concentrations of Cd in the leaves of the plants were compared after 10 d of cultivation. Anatomical analyses of Tritonia roots were performed using appropriately stained freehand cross-sections.


RESULTS
The process of contraction required specific anatomical adaptation of the root base in Tritonia, with less lignified and less suberized tissues in comparison with the subapical part of the root. These unusual developmental characteristics were accompanied by more intensive translocation of Cd ions from the basal part of contractile roots to the leaves than from the apical-subapical root parts. The opposite effects were seen in the non-contractile roots of maize, with higher uptake and transport by the apical parts of the root and lower uptake and transport by the basal part.


CONCLUSIONS
The specific characteristics of contractile roots may have a significant impact on the uptake of ions, including toxic metals from the soil surface layers. This may be important for plant nutrition, for example in the uptake of nutrients from upper soil layers, which are richer in humus in otherwise nutrient-poor soils, and also has implications for the uptake of surface-soil pollutants.
Department of Plant Physiology, Faculty of Natural Sciences, Comenius University in Bratislava, Mlynská dolina B2, 842 15 Bratislava, Slovak Republic, Institute of Chemistry, Slovak Academy of Sciences, Dúbravská cesta 9, Bratislava 845 38, Slovak Republic, Research Centre for Plant Growth and Development, School of Biological and Conservation Sciences, University of KwaZulu-Natal Pietermaritzburg, Private Bag X01, Scottsville 3209, South Africa and Institute of Botany, Slovak Academy of Sciences, Dúbravská cesta 9, Bratislava 845 23, Slovak Republic Department of Plant Physiology, Faculty of Natural Sciences, Comenius University in Bratislava, Mlynská dolina B2, 842 15 Bratislava, Slovak Republic, Institute of Chemistry, Slovak Academy of Sciences, Dúbravská cesta 9, Bratislava 845 38, Slovak Republic, Research Centre for Plant Growth and Development, School of Biological and Conservation Sciences, University of KwaZulu-Natal Pietermaritzburg, Private Bag X01, Scottsville 3209, South Africa and Institute of Botany, Slovak Academy of Sciences, Dúbravská cesta 9, Bratislava 845 23, Slovak Republic lux@fns.uniba.sk.
Alexander
A
Lux
Department of Plant Physiology, Faculty of Natural Sciences, Comenius University in Bratislava, Mlynská dolina B2, 842 15 Bratislava, Slovak Republic, Institute of Chemistry, Slovak Academy of Sciences, Dúbravská cesta 9, Bratislava 845 38, Slovak Republic, Research Centre for Plant Growth and Development, School of Biological and Conservation Sciences, University of KwaZulu-Natal Pietermaritzburg, Private Bag X01, Scottsville 3209, South Africa and Institute of Botany, Slovak Academy of Sciences, Dúbravská cesta 9, Bratislava 845 23, Slovak Republic.
Andrej
A
Lackovič
Department of Plant Physiology, Faculty of Natural Sciences, Comenius University in Bratislava, Mlynská dolina B2, 842 15 Bratislava, Slovak Republic, Institute of Chemistry, Slovak Academy of Sciences, Dúbravská cesta 9, Bratislava 845 38, Slovak Republic, Research Centre for Plant Growth and Development, School of Biological and Conservation Sciences, University of KwaZulu-Natal Pietermaritzburg, Private Bag X01, Scottsville 3209, South Africa and Institute of Botany, Slovak Academy of Sciences, Dúbravská cesta 9, Bratislava 845 23, Slovak Republic.
Johannes
J
Van Staden
Department of Plant Physiology, Faculty of Natural Sciences, Comenius University in Bratislava, Mlynská dolina B2, 842 15 Bratislava, Slovak Republic, Institute of Chemistry, Slovak Academy of Sciences, Dúbravská cesta 9, Bratislava 845 38, Slovak Republic, Research Centre for Plant Growth and Development, School of Biological and Conservation Sciences, University of KwaZulu-Natal Pietermaritzburg, Private Bag X01, Scottsville 3209, South Africa and Institute of Botany, Slovak Academy of Sciences, Dúbravská cesta 9, Bratislava 845 23, Slovak Republic.
Desana
D
Lišková
Department of Plant Physiology, Faculty of Natural Sciences, Comenius University in Bratislava, Mlynská dolina B2, 842 15 Bratislava, Slovak Republic, Institute of Chemistry, Slovak Academy of Sciences, Dúbravská cesta 9, Bratislava 845 38, Slovak Republic, Research Centre for Plant Growth and Development, School of Biological and Conservation Sciences, University of KwaZulu-Natal Pietermaritzburg, Private Bag X01, Scottsville 3209, South Africa and Institute of Botany, Slovak Academy of Sciences, Dúbravská cesta 9, Bratislava 845 23, Slovak Republic.
Jana
J
Kohanová
Department of Plant Physiology, Faculty of Natural Sciences, Comenius University in Bratislava, Mlynská dolina B2, 842 15 Bratislava, Slovak Republic, Institute of Chemistry, Slovak Academy of Sciences, Dúbravská cesta 9, Bratislava 845 38, Slovak Republic, Research Centre for Plant Growth and Development, School of Biological and Conservation Sciences, University of KwaZulu-Natal Pietermaritzburg, Private Bag X01, Scottsville 3209, South Africa and Institute of Botany, Slovak Academy of Sciences, Dúbravská cesta 9, Bratislava 845 23, Slovak Republic Department of Plant Physiology, Faculty of Natural Sciences, Comenius University in Bratislava, Mlynská dolina B2, 842 15 Bratislava, Slovak Republic, Institute of Chemistry, Slovak Academy of Sciences, Dúbravská cesta 9, Bratislava 845 38, Slovak Republic, Research Centre for Plant Growth and Development, School of Biological and Conservation Sciences, University of KwaZulu-Natal Pietermaritzburg, Private Bag X01, Scottsville 3209, South Africa and Institute of Botany, Slovak Academy of Sciences, Dúbravská cesta 9, Bratislava 845 23, Slovak Republic.
Michal
M
Martinka
D002104:Cadmium / Q000378:metabolism*; D027621:Iridaceae / Q000033:anatomy & histology / Q000378:metabolism*; D018515:Plant Leaves / Q000737:chemistry; D018517:Plant Roots / Q000033:anatomy & histology / Q000378:metabolism*; D012989:Soil Pollutants / Q000378:metabolism*; D003313:Zea mays / Q000033:anatomy & histology / Q000378:metabolism*
D012989:Soil Pollutants; D002104:Cadmium
Apoplasmic barrier; Casparian band; Cd; Tritonia gladiolaris; Zea mays; cadmium; contractile roots; endodermis; heavy metal uptake; maize; root translocation; soil pollution