Differential tissue-specific expression of cysteine proteinases forms the basis for the fine-tuned mobilization of storage globulin during and after germination in legume seeds

The temporal and spatial distribution of cysteine proteinases (CPRs) was an alyzed immunologically and by in situ hybridization to identify the CPRs in volved in the initiation of storage-globulin degradation in embryonic axes and cotyledons of germinating vetch (Vicia sati,ta L.). At the start of ger mination several CPRs were found in protein bodies in which they might have been stored in the mature seeds. Cysteine proteinase 1 was predominantly f ound in organs like the radicle, which first start to grow during germinati on. Cysteine proteinase 2 was also present at the start of germination but displayed a less-specific histological pattern. Proteinase B was involved i n the globulin degradation of vetch cotyledons as well. The histological pa ttern of CPRs followed the distribution of their corresponding mRNAs. The l atter were usually detected earlier than the CPRs but the in situ hybridiza tion signals were histologically not as restricted as the immunosignals. Pr oteolytic activity started in the radicle of the embryonic axis early durin g germination. Within 24 h after imbibition it had also spread throughout t he whole shoot. At the end of germination. newly synthesized CPRs might hav e supplemented the early detectable CPRs in the axis. In the cotyledons, on ly the abaxial epidermis and the procambial strands showed proteinase local ization during germination. Both CPR1 and CPR2, as well as the less common proteinase B, might have been present as stored proteinases. Three days aft er imbibition, proteolytic activity had proceeded from the cotyledonary epi dermis towards the vascular strands deeper inside the cotyledons. The histo chemical detection of the CPRs was in accordance with the previously descri bed histological pattern of globulin mobilization in germinating vetch [Tie demann J, et al. (2000)1]. A similar link between the distribution of CPRs and globulin degradation was found in germinating seeds of Phaseolus vulgar is L. The coincidence of the histological patterns of globulin breakdown wi th that of the CPRs indicates that at least CPR1, CPR2 and proteinase B are responsible for bulk globulin mobilization in the seeds of the two legumes .