Abstract: Using differential screening of a leaf eDNA library prepared from a bean cultivar (Phaseolus vulgaris L. tv. Saxa) exposed to HgCl2, the authors have isolated and characterized two heavy metal-regulated eDNA fragments, designated as PvSR5 and PvSRS1 (Phaseolus vulgaris stress-related gene). The sequences of the eDNA inserts and homological analysis showed that both PvSR5 and PvSR51 encode a polyubiquitin respectively. The polyubiquitin genes were constitutively expressed in roots but weakly expressed in stems and leaves. Northern blot analysis revealed a low level of transcripts of polyubiquitin in unstressed bean leaves, but the 'gene expression was strongly stimulated by heavy metals, elevated temperature and salicylic acid, whereas wounding had almost no effect. These suggested that polyubiquitin might play important roles in resistance to heavy metals and various environmental stresses.

Key words: Heavy metals, Polyubiquitin, Phaseolus vulgaris