Identification and localization of vegetative storage proteins in legume leaves

Leaves from 12 legume species representing two subtribes were examined by various techniques for the presence of vegetative storage proteins (VSPs) similar to the 27, 29, and 94 kD VSPs of soybean. Polyacrylamide gel electrophoresis (PAGE) of leaf protein followed by western immunoblotting using antibody that recognizes soybean VSP94, a lipoxygenase, demonstrated that this protein is present in six of the nine species tested. Blotting with antibody to soybean VSP27/29, which are glycoproteins, gave labelling in seven species and glycoprotein affino-blots showed that glycosylated proteins ranging around 27 to 29 kD were present in all nine species examined. Immunocytochemical localization studies of eight species demonstrated that proteins antigenically similar to VSP94 and VSP27/29 are specifically accumulated in the vacuole of paraveinal mesophyll (PVM) cells. They were not detectable at significant levels in other mesophyll cells using this technique. Comparisons of protein compositions of isolated PVM and mesophyll protoplasts from seven species further confirmed the specialized nature of the PVM. VSP94 and proteins ranging from 25 to 35 kD molecular mass were the major proteins of PVM of all but one species while Rubisco was quite low in amount compared to mesophyll protoplasts. The results show that VSP synthesis and accumulation is a general feature of legume leaves containing a PVM layer and indicate that the PVM plays a specialized role in nitrogen metabolism and partitioning in these species.