Effects of tamoxifen on the electron transport chain of isolated rat liver mitochondria.

Tamoxifen (and 4-hydroxytamoxifen), a nonsteroidal triphenylethylene antiestrogenic drug widely used in the treatment of breast cancer, interacts strongly with the respiratory chain of isolated rat liver mitochondria. The drug acts as both an uncoupling agent and a powerful inhibitor of electron transport. Tamoxifen brings about a collapse of the membrane potential. Enzymatic assays and spectroscopic studies indicate that tamoxifen inhibits electron transfer in the respiratory chain at the levels of complex III (ubiquinol-cytochrome-c reductase) and, to a lesser extent, of complex IV (cytochrome-c oxidase). The activities can be restored by the addition of diphosphatidylglycerol, a phospholipid implicated in the functioning of the respiratory chain complexes.

Aging and regreening in soybean cotyledons. 1 Ultrastructural changes in plastids and plastoglobuli.

Ultrastructural changes were studied in plastids from mature, partially senescent, senescent, and regreened soybean cotyledons. Tissues were fixed for electron microscopy and also plastoglobuli were isolated from 14-, 16-, and 23-day-old tissues as well as from tissues which had been regreened. In mature tissues, the mesophyll, as compared to the palisade parenchyma, plastids have a poorly developed lamellar system. At the beginning of senescence there occurred an increase in the size of granal stacks and in the size and number of plastoglobuli. At late stages of senescence there is a breakdown of thylakoids. During regreening there is a recovery of the chloroplast fine structure. Plastoglobuli isolated from senescent cotyledons were large and appeared wrinkled when observed with a scanning electron microscope unlike those isolated from mature tissues which were spherical. Chloroplasts in regreened tissues originate either from proplastids or from intermediate stages of slightly senescent plastids.

[Comparative analysis of ultrastructure and lipid composition of plastids from sun and shade plants (author's transl)]. / Analyse comparative de l'ultrastructure et de la composition lipidique des chloroplastes de plantes d'ombre et de soleil.

The ultrastructure and lipid composition of chloroplasts, isolated from various shade and sun plants, were compared. Depending on the origin of the plastid, significant differences were observed in the percentage of appressed thylakoids. Accordingly, plastids could be classified into three different types: Type I chloroplasts, from mesophyll cells of sun plants (barley, corn, spinach, bean), display well-developed grana and intergrana thylakoid membranes. Type II chloroplasts, typical of shade plant (Arum), show giant grana stacks with few interconnecting thylakoids. Type III chloroplasts, from bundle sheath cells of leaves from C4-plants (corn), are characterized by an extensive development of stroma thylakoids with only occasional rudimentary grana. The percentages of appressed membranes are in the ranges of 50 to 60%, 80% and 2% for type I, II and III plastids respectively. Striking differences are observed in the fatty acid composition of phosphatidylglycerol molecules. Trans-delta3-hexadecenoic acid is found only in this phospholipid and amounts to 30 to 40%, 50% and less than 8% of total fatty acids in type I, II and III plastids respectively. The comparison of ultrastructural and biochemical data suggests a strong correlation between the amounts of phosphatidylglycerol molecules containing trans-delta3-hexadecenoic acid and the percentages of appressed membranes (grana stacks) within plastid stroma.