The Structure and Function of Grana-Free Thylakoid Membranes in Gerontoplasts of Senescent Leaves of Vicia faba L

H. Oskar Schmidt Zentralinstitut für Genetik und Kulturpflanzenforschung der AdW der DDR, 4325 Gatersleben Z. Naturforsch. 43c, 149-154 (1988); received March 11/September 7, 1987 Senescence, Chloroplast, Gerontoplast, Thylakoid Membrane Proteins, Electronmicroscopy, Photosynthesis In the course of yellowing (senescence) the leaves of Vicia faba L. lose 95% of their chlorophyll. Gerontoplasts develop from chloroplasts and aggregate with the pycnotic mitochondria and the cell nucleus in the senescent cells (organelle aggregation). The gerontoplasts contain only a few, unstacked thylakoid membranes but a large number of carotinoid-containing plastoglobuli, which after the degration of chlorophyll presumably assume the light protection of the cells. The thylakoid membranes of the gerontoplasts were isolated by means of a flotation method. Their polypeptide composition is characterized by a high proportion of light-harvesting complex. Evidence of relatively high photochemical activity shows that functional thylakoid membranes are present in the premortal senescence state of leaves and this suggests that there is functional compartmentation of the hydrolytic processes in this stage of the leaves' development.