In seedlings of the heavy metal accumulator Brassica juncea Cu2+ differentially affects transcript amounts for gamma-glutamylcysteine synthetase (gamma-ECS) and metallothionein (MT2).
Glutathione (GSH) is the precursor of the phytochelatins (PC), which in plants and fungi are involved in heavy metal sequestration. The regulatory enzyme gamma-glutamylcysteine synthetase (gamma-ECS) catalyzes the first step in GSH biosynthesis. For the heavy metal accumulator Brassica juncea L. a partial gamma-ECS cDNA was cloned by RT-PCR. Treatment of suspension-cultured dark grown seedlings with micromolar concentrations of CuSO4 resulted in a strong increase of gamma-ECS mRNA in roots and shoots, concomitant with an increase of GSH and phytochelatins. A significant up-regulation of gamma-ECS mRNA was observed at 25 microM CuSO4 (shoot growth: -11%), whereas maximum up-regulation was obtained at 100 microM CuSO4 (shoot growth: -60%). Unexpectedly, metallothionein 2 (MT2) mRNA was decreased in response to the CuSO4 treatments. CdSO4 at a concentration of 50 microM caused a 72% reduction in shoot growth without affecting the amounts of gamma-ECS- and MT2 mRNAs. ZnSO4 at a concentration of 500 microM did not reduce growth but induced transient increases of gamma-ECS- and MT2 mRNAs. The implications of the results with respect to differential regulation of gamma-ECS and MT2 during heavy metal exposure are discussed.
Schäfer
H J
HJ
Botanisches Institut, Heidelberg, Germany.
Greiner
S
S
Rausch
T
T
Haag-Kerwer
A
A
D017360:Arabidopsis / Q000187:drug effects / Q000378:metabolism; D001483:Base Sequence; D001937:Brassica / Q000187:drug effects / Q000378:metabolism*; D019187:Cadmium Compounds / Q000494:pharmacology; D003001:Cloning, Molecular; D003300:Copper / Q000494:pharmacology*; D019327:Copper Sulfate / Q000494:pharmacology; D017931:DNA Primers; D018506:Gene Expression Regulation, Plant / Q000187:drug effects*; D005721:Glutamate-Cysteine Ligase / Q000096:biosynthesis*; D008668:Metallothionein / Q000187:drug effects*; D008969:Molecular Sequence Data; D018515:Plant Leaves; D018517:Plant Roots; D016133:Polymerase Chain Reaction; D012333:RNA, Messenger / Q000096:biosynthesis; D011993:Recombinant Fusion Proteins / Q000096:biosynthesis; D013431:Sulfates / Q000494:pharmacology; D014158:Transcription, Genetic / Q000187:drug effects*; D019287:Zinc Sulfate / Q000494:pharmacology
D019187:Cadmium Compounds; D017931:DNA Primers; D012333:RNA, Messenger; D011993:Recombinant Fusion Proteins; D013431:Sulfates; D019287:Zinc Sulfate; D003300:Copper; D008668:Metallothionein; C037123:cadmium sulfate; D005721:Glutamate-Cysteine Ligase; D019327:Copper Sulfate