Cloning sulfur assimilation genes of Brassica juncea L.:: cadmium differentially affects the expression of a putative low-affinity sulfate transporter and isoforms of ATP sulfurylase and APS reductase

被引:126
作者
Heiss, S [1 ]
Schäfer, HJ [1 ]
Haag-Kerwer, A [1 ]
Rausch, T [1 ]
机构
[1] Heidelberg Univ, Inst Bot, D-69120 Heidelberg, Germany
关键词
sulfate assimilation; low-affinity sulfate transporter; ATP sulfurylase; APS reductase; myrosinase; cadmium; Brassica juncea L;
D O I
10.1023/A:1006169717355
中图分类号
Q5 [生物化学]; Q7 [分子生物学];
学科分类号
071010 ; 081704 ;
摘要
The heavy-metal accumulator Brassica juncea L. is a high-biomass crop able to extract heavy-metal ions from the soil, a substantial part being translocated from root to shoot. Previous work has shown that Cd accumulation is accompanied by massive formation of phytochelatins (PCs). Rapid de novo synthesis of PCs in roots and leaves requires an increased synthesis of the tripeptide glutathione (GSH), which in turn depends on increased sulfur assimilation. Therefore, we have cloned cDNAs for three enzymes involved in sulfur assimilation, i.e. a putative low-affinity sulfate transporter (LAST) and two isoforms each for ATP sulfurylase (ATPS) and APS reductase (APSR). As degradation of glucosinolates might provide an additional sulfur source under stress, we also cloned a myrosinase (MYR). RNA blot analysis of transcript amounts indicated that upon Cd exposure (25 mu M) the expression of ATPS and APSR in roots and leaves of 6-week-old Brassica juncea plants was strongly increased, whereas the expression of MYR was unaffected. LAST transcripts were significantly reduced in the root but remained unchanged in the leaves. Concomitant with Cd induction of ATPS and APSR mRNAs, cysteine concentrations in roots and leaves increased by 81% and 25%, respectively, whereas GSH concentrations decreased in roots and leaves by 39% and 48%, respectively. In agreement with our previous report on Cd induction of gamma-glutamylcysteine synthetase in B. juncea, the results indicate coordinate changes of expression for several sulfur assimilation enzymes in response to an increased demand for cysteine during PC synthesis.
引用
收藏
页码:847 / 857
页数:11
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