Cadmium inhibits the induction of high-affinity nitrate uptake in maize (Zea mays L.) roots

Planta. 2012 Dec;236(6):1701-12. doi: 10.1007/s00425-012-1729-4. Epub 2012 Aug 5.

Abstract

Cadmium (Cd) detoxification involves glutathione and phytochelatins biosynthesis: the higher need of nitrogen should require increased nitrate (NO(3)(-)) uptake and metabolism. We investigated inducible high-affinity NO(3)(-) uptake across the plasma membrane (PM) in maize seedlings roots upon short exposure (10 min to 24 h) to low Cd concentrations (0, 1 or 10 μM): the activity and gene transcript abundance of high-affinity NO(3)(-) transporters, NO(3)(-) reductases and PM H(+)-ATPases were analyzed. Exposure to 1 mM NO(3)(-) led to a peak in high-affinity (0.2 mM) NO(3)(-) uptake rate (induction), which was markedly lowered in Cd-treated roots. Plasma membrane H(+)-ATPase activity was also strongly limited, while internal NO(3)(-) accumulation and NO(3)(-) reductase activity in extracts of Cd treated roots were only slightly lowered. Kinetics of high- and low-affinity NO(3)(-) uptake showed that Cd rapidly (10 min) blocked the inducible high-affinity transport system; the constitutive high-affinity transport system appeared not vulnerable to Cd and the low-affinity transport system appeared to be less affected and only after a prolonged exposure (12 h). Cd-treatment also modified transcript levels of genes encoding high-affinity NO(3)(-) transporters (ZmNTR2.1, ZmNRT2.2), PM H(+)-ATPases (ZmMHA3, ZmMHA4) and NO(3)(-) reductases (ZmNR1, ZmNADH:NR). Despite an expectable increase in NO(3)(-) demand, a negative effect of Cd on NO(3)(-) nutrition is reported. Cd effect results in alterations at the physiological and transcriptional levels of NO(3)(-) uptake from the external solution and it is particularly severe on the inducible high-affinity anion transport system. Furthermore, Cd would limit the capacity of the plant to respond to changes in NO(3) (-) availability.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Biological Transport
  • Cadmium / analysis
  • Cadmium / pharmacology*
  • Cell Membrane / enzymology
  • Gene Expression Regulation, Plant / drug effects*
  • Kinetics
  • Nitrate Reductase / genetics
  • Nitrate Reductase / metabolism
  • Nitrates / analysis
  • Nitrates / metabolism*
  • Nitrogen / metabolism
  • Plant Proteins / genetics*
  • Plant Proteins / metabolism
  • Plant Roots / drug effects
  • Plant Roots / genetics
  • Plant Roots / metabolism
  • Plant Shoots / drug effects
  • Plant Shoots / genetics
  • Plant Shoots / metabolism
  • Proton-Translocating ATPases / genetics
  • Proton-Translocating ATPases / metabolism
  • RNA, Messenger / genetics
  • RNA, Plant / genetics
  • Seedlings / drug effects
  • Seedlings / genetics
  • Seedlings / metabolism
  • Zea mays / drug effects*
  • Zea mays / genetics
  • Zea mays / metabolism

Substances

  • Nitrates
  • Plant Proteins
  • RNA, Messenger
  • RNA, Plant
  • Cadmium
  • Nitrate Reductase
  • Proton-Translocating ATPases
  • Nitrogen