Influence of temperature, cholesterol, dipalmitoyllecithin and Ca on the rate of muscle cell fusion

The rate of muscle cell fusion increases between 28 °C and 40 °C by a factor of 15 to 20. The formal activation energy of the fusion process changes abruptly at about 35 °C. This change is discussed in terms of a phase transition of the membrane lipids at 35 °C. In the presence of cholesterol or dipalmitoyllecithin the fusion rate decreases markedly. Increasing the temperature reverses the effects of cholesterol and dipalmitoyllecithin. These results are discussed in terms of interactions between membrane lipids.     

Feinstruktur der Pollenschläuche im Griffel vonPetunia

Summary From electron microscopic observation of transverse sections through the style ofPetunia it was possible to show that the pollen tubes grow within the compact matrix of the middle lamellae of the transmitting tissue. This it does enzymatically by dissolving a pipelike path in front of the tube tip. From the fine structure of the cytoplasm and the organelle content, the cells of the tubes and of the transmitting tissue can be distinguished. Differences in the fine structure of the cytoplasm and the wall between inhibited (incompatible) and normal growing (compatible) pollen tubes can be demonstratedin situ. This is discussed in terms of localisation of the incompatibility reaction on the surface of the inhibited pollen tubes. The interpretation is in agreement with genetical and biochemical observations elsewhere.