Effects of nanomolar heavy metal concentrations on plants - comparison of biochemical&biophysical mechanisms of deficiency and sublethal toxicity under environmentally relevant conditions

• Applicant: Professor Dr. Hendrik Küpper
• Subject Area: Plant Biochemistry and Biophysics ; Plant Cultivation, Plant Nutrition, Agricultural Technology ; Plant Physiology
• Term: from 2010 to 2015
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 169833033

• Final Report Year: 2015

Final Report Abstract

This project led to many important results, as documented by the various publications originating from it. The field study with simulation in the lab revealed that in soft water conditions strong synergy exists between toxic effects of cadmium and nickel, so that combinations of these metals become severely toxic at concentrations where the individual metals do not lead to any toxicity. In the investigation of arsenic toxicity, a key finding was that a specific inhibition of chlorophyll synthesis takes place very early in the sequence of events before any other inhibition became measurable, while oxidative stress only occurred as a rather late consequence of a malfunctioning of photosynthesis and thermal dissipation of captured energy. Arsenic accumulation in tissues changed in location and speciation during the transition from sublethally toxic to lethal treatments. In the case of cadmium and copper, a key finding was that phytochelatin synthesis is essentially zero when work is performed under ultraclean conditions leading to lower basal metal concentrations than usually achieved in earlier studies. This is important as it was long debated whether phytochelatins have physiological a physiological role independent of metal detoxification, which now seems not the case. Both cadmium and copper toxicity changed the distribution of micronutrients in the tissue, but in different ways. In case of copper it is remarkable that (in contrast to arsenic, see above) pigment loss in the plants was only observed as a late consequence of the stress, while specific inhibition of the PSII reaction centre was the first damage measured in high light. Also cadmium strongly inhibited the PSII reaction centre already at sublethal concentrations, but in addition it led to inhibition of the Calvin cycle. In low light, by metalloproteomics for the first time we could show that already at low nanomolar concentrations Cd binds to LHCII as high-affinity target. For chromium, the most important result is that the current data suggest a beneficial or even essential role in plants, where it was previously regarded as nonessential. Identification of three high affinity Cr-binding proteins by metalloproteomics furthermore suggests a role of all three proteins in carbohydrate binging and pathogen resistance. My work as a whole, not only this particular project, was subject of some media coverage when I moved to Budweis, Czech Republic. In July and August last year there were articles in several Czech national and regional newspapers and magazines, as well as on national and regional TV and radio. These articles were also related to a decision of the Czech Ministry of Education to cut funding for a programme aimed at attracting scientists from abroad, where I highlighted as a positive contrast the very reliable funding by the DFG, which is only based on scientific, not political considerations.

Publications

• (2013) Cadmium Toxicity in Plants. In: Cadmium: From Toxicity to Essentiality, Chapter 13, Volume 11 of series "Metal Ions in Life Sciences". (Eds: Sigel A, Sigel H, Sigel RKO). Springer Science + Business Media B.V., Dordrecht; pp. 395-414
  Andresen E, Küpper H
  
• (2013) Different strategies of cadmium detoxification in the submerged macrophyte Ceratophyllum demersum L. Metallomics 5, 1377-1386
  Andresen E, Mattusch J, Wellenreuther G, Thomas G, Abad UA, Küpper H
  
• (2013) Effects of Cd & Ni toxicity to Ceratophyllum demersum under environmentally relevant conditions in soft & hard water including a German lake. Aquatic Toxicology 142-143, 387- 402
  Andresen E, Opitz J, Thomas G, Stärk H-J, Dienemann H, Jenemann K, Dickinson BC, Chang CJ, Küpper H
  
• (2013) Effects of nanomolar copper on water plants - comparison of biochemical and biophysical mechanisms of deficiency and sublethal toxicity under environmentally relevant conditions. Aquatic toxicology 140-141, 27-36
  Thomas G, Stärk H-J, Wellenreuther G, Dickinson BC, Küpper H
  
• (2013) Speciation and distribution of arsenic in the non-hyperaccumulator macrophyte Ceratophyllum demersum L. Plant Physiology 163, 1396-1408
  Mishra S, Wellenreuther G, Mattusch J, Stärk H-J, Küpper H
  
• (2013) Toxicity and deficiency of copper in Elsholtzia splendens affect photosynthesis biophysics, pigments and metal accumulation. Environmental Science and Technology 47, 6120-6128
  Peng H, Kroneck PMH, Küpper H
  
• (2014) A different sequence of events than previously reported leads to arsenic-induced damage in Ceratophyllum demersum L. Metallomics 6, 444-454
  Mishra S, Stärk H-J, Küpper H
  
• Biochemical and physiological evidence characterising chromium as a new essential ultra-micronutrient. Journal of Biological Inorganic Chemistry,19, S726 (abstract; conference talk at the EuroBIC conference in Zurich in August 2014)
  Küpper H, Mattusch J, Peiter E, Schmelzer C, Stärk H.-J.