Flower colour is determined primarily by the production of pigments, usually anthocyanins or carotenoids, but the shade and intensity of the colour are often changed by other factors such as vacuolar compounds, pH and metal ions. Pigmentation can also be affected by the shape of epidermal cells, especially those facing prospective pollinators. A conical shape is believed to increase the proportion of incident light that enters the epidermal cells, enhancing light absorption by the floral pigments, and thus the intensity of their colour. We have identified a gene (mixta) that affects the intensity of pigmentation of epidermal cells in Antirrhinum majus petals. The cells of the corolla lobes fail to differentiate into their normal conical form in mixta mutants. We have cloned the mixta gene by transposon tagging; its sequence reveals that it encodes a Myb-related protein that probably participates in the transcriptional control of epidermal cell shape.

The membrane potential of frog sartorius muscle fibers in a Cl- and Na-free Ringer's solution when sucrose replaces NaCl is about the same as that in normal Ringer's solution. The K+ efflux is also about the same in the two solutions but muscles lose K and PO4 in sucrose Ringer's solutions. The membrane potential in sucrose Ringer's solution is equal to that given by the Nernst equation for a K+ electrode, when corrections are made for the activity coefficients for K+ inside and outside the fiber. For a muscle in normal Ringer's solution, the measured membrane potential is within a few millivolts of EK. This finding is incompatible with a 1:1 coupled Na-K pump. It is consistent with either no coupling of Na efflux to K influx, or a coupling ratio of 3 or greater.

No abstract

To examine the effect of so-called "concentration polarization" on the performance of a membrane reactor with a highly hydrogen-permeable membrane, methane steam reforming was conducted, using a Pd/Ag membrane with a thickness of a few micrometers. First, the relation between the methane conversion and the hydrogen recovery was experimentally examined, and the relation was compared with that predicted by a rather simple simulation that assumes the instant achievement of equilibrium. When the hydrogen recovery was smallest, the experimental results agreed well with the simulation results. With increasing reaction pressure, the experimental methane conversion became lower than the simulated conversion. These results suggest that the reaction is limited by reduced hydrogen removal, because of the concentration polarization. The influence of concentration polarization was confirmed by the comparison of the experimental results of hydrogen permeation from a mixture of H 2 and N 2 with the simulation results based on the plug-flow model. It then was experimentally attempted to reduce the concentration polarization by changing the configuration of the reactor. The methane conversion was successfully improved using reactors that had narrower inner diameters and baffle plates, probably because of the reduction in concentration polarization. It was concluded that the reactor configuration was quite essential to make the best use of a membrane reactor with a highly permeable membrane.