Immunogold Localization and Quantitative Distribution of Two Proteins of the Glycine Decarboxylase Complex in Developing Leaflets of Pea (Pisum sativum L.)

Abstract

We investigated the distribution of the P- and H-proteins of the glycine decarboxylase complex (EC 2.1.2.10) in developing pea (Pisum sativum L.) leaflets using immunogold techniques. Antibodies to these two proteins did not bind to young, nonphotosynthetic cells. Once the leaflet turned green, the labeling density in the mitochondria of the mesophyll cells increased substantially. Few particles were found in the mitochondria of the paraveinal mesophyll and guard cells. None were found either in the epidermis or in the parenchyma of the vascular tissue. Thus leaflets not yet exposed to light, and nonphotosynthetic cells, do not express these two proteins needed for photorespiration. The process of photorespiration seems to be correlated with the photosynthetic state of the cell and of the organ. It was also found to be positively linked with the integrity of the chloroplast since the highest label density obtained in the mitochondria was found just before the onset of ultrastructural senescence in the chl...