In this paper, the fluorescent mRNA differential display (DD) technique was applied to analyze transcriptional regulation in response to Cd treatment in a heavy-metal accumulator, Brassica juncea. 154 DD bands were identified, of which fragments corresponding to 15 and 13 cDNAs were successfully cloned from leaves and roots, respectively. Many of the genes were confirmed to have a 2-5 fold increase in expression in both roots and leaves after 48h Cd exposure (～22.4ppm). However, several isolated genes, e.g., DD2, DD21, DD22, showed a reversed mRNA expression pattern. Sequencing revealed those Cd-induced up-regulated genes displayed mRNAs corresponding to 19 different genes, 18 of which had a clear identity to Arabidopsis thaliana sequences and a putative function was assigned to 15 of them, including the auxin-responsive GH3, ARF-like small GTPases/ARFs, ARD/ARD, APS reductase, Nop, catalase, zinc finger (C3HC4-type RING finger), diacylglycerol kinase, and haloacid dehalogenase-like hydrolase families. Three cDNAs corresponded to predicted membrane proteins (KOG3491) or a ribosome-associated membrane protein RAMP4. One other clone, DD26, did not show significant identities to any translated sequence in the GenBank database, suggesting it may either encode unidentified proteins, or correspond to un-translated, non-conserved regions of mRNA molecules. These Cdresponsive up-regulated genes are mostly also regulated by abiotic or biotic stresses, e.g., dehydration, chilling, high salt, auxin, heat and infection, in other plants. The present study leads to an increased understanding of genes and/or the biochemical pathways involved in heavy-metal resistance and accumulation in plants.

A clone of PvSR6 encoding a new member of the DnaJ-like protein family was isolated from a mer-curic-chloride-treated bean (Phaseolus vulgaris L.) cDNA library by differential screening using cDNAs derived from treated and untrested plants. The predicted protein contains the highly conserved J domain only, which is present in all DnaJ-like proteins and is considered to play a critical role in DnaJ protein-protein interactions. PvSR6 gene is constitu-tively expressed in rots but weakly expressed in stems and leaf tissue. Northern blot analysis revealed the transcripts of PvSR6 were at low levels in unstressed tean leaves, but the genes expression was strongly stimulated by heavy metals. These suggest that the PvSR6 might play an important role in resistance to the damage caused by heavy metals.

以PvSR6cDNA编码一种菜豆DnaJ-like蛋白，并利用PCR的方法克隆出基因组部分序列，核苷酸序列分析表明PvSR6基因在这段编码区内无内含子；Southern blot分析表明菜豆基因组中存在多个PvSR6基因拷贝；Northern blot分析结果表明PvSR6是组成型表达蛋白，重金属Hg、Cd和As，过量的Cu和Zn及受伤、高温、病毒侵染和水杨酸等均能强烈地诱导其基因在叶片中的表达，表明DnaJ-like蛋白与植物的抗逆性有关。

差别筛选HgCl2胁迫处理的菜豆（Phaseolusvu lgaris L.）幼苗叶片cDNA库，分离出1个重金属胁迫响应基因PvSR52克隆，其cDNA长度为281bp。cDNA和氨基酸序列同源性分析表明PvSR52编码一种多聚泛肽。Southern blot结果表明菜豆泛肽可能由少数基因编码。Northern blot分析表明多聚泛肽叶片中表达较少；重金属Hg、Cd和As 等、过量的Zn和Cu及高温、病毒侵染和水杨酸等环境胁迫均能强烈地刺激其在叶片中的表达。推测泛肽水解系统在提高植物的抗逆性方面有重要作用。

为探讨植物抗重金属的分子机理，差别筛选了HgCl2胁迫的菜豆（Phaseolus vulg a ris L1）叶片cDNA库，分离出一个重金属胁迫响应基因PvSR4克隆LcDNA和氨基酸序列分析表明PvSR4编码一种细胞内病程相关蛋白，该蛋白具有RNase活性LNo rthern blot分析表明PvSR4基因在正常生长条件下的叶片中不表达，重金属（Hg、Cd、As、Zn和Cu等）和水杨酸能强烈地诱导其基因的表达，受伤也能促进该基因的转录，而热胁迫几乎没有调节作用L推测PvSR4蛋白在诱导植物的抗逆性和抵抗重金属胁迫方面有重要作用。