ALBERT

Notes: Can road pricing be made popular? Phillip Goodwin, director of the Oxford University Transport Studies Group, explains how road pricing could be made popular with the electorate - and politicians.

Notes: Cell-to-cell communication in lateral branches of limited growth in male Chara corallina plants has been studied using fluorescent plasmalemma-impermeable probes. The extent of cell-to-cell communication was found to be seasonal. In winter, branch internodes were characterized by relatively low plasmalemma potential differences (–121·2±23·2 mV; [K+]o 0·5 mol m−3; pH 7·6), quiescent dactyls isolated from the symplast (conic tips) and by restricted cell-cell communication (frequency of intercellular transport of six carboxyfluorescein = 42·9%). Cell-to-cell communication was inhibited during action-potentials, and was more extensive between cells which did not give an action potential in response to a current pulse. An inhibitor of the action potential, La3+, promoted cell-to-cell communication. These may be characteristic features of winter dormancy in lateral branches of Chara. In spring, morphological and electrophysiological changes occurred immediately prior to the onset of fertility. Characteristic changes in morphology included increased abundance of spherosomes and glycosomes, elongation of stipulodes and development of active branch dactyls. Spring branch inter-nodes were characterized by high plasmalemma PDs (–210·5±30·8mV; [K+]o 0·5 mol m−3; pH 7·6), predominantly active, non-isolated dactyls (spinaceous tips), and extensive intercellular communication (frequency of intercellular transport of 6 carboxyfluorescein = 89·2%). Artificial elevation of the intracellular calcium ion concentration by application of ionophore A23187 or Ca2+ microinjection significantly restricted intercellular communication to a level similar to that found in winter. The depression of intercellular communication in winter tissues is suggested to be due to high sensitivity to action potentials and/or to Ca2+ fluxes. Changes in intracellular Ca2+ distribution may be involved in the transition between the morphologically distinct states of dormancy and incipient fertility.

Notes: Abstract. The fluorescent probes 6–carboxyfluorescein and lucifer yellow CH which do not pass the plasmalemma have been used to examine cell-to-cell communication in the leaf of Commelina cyanea. Dye movement from cell-to-cell occurs in epidermal, spongy and palisade mesophyll, and vascular cells. Dye movement between these tissues was also found. Hence, the epidermis, spongy and palisade mesophyll cells, and vascular tissue are all linked in a continuous symplast. However, dye injected into the epidermal cells rarely moves into guard cells, indicating that these cells are relatively isolated from the surrounding cells. In the same way, guard cells in Vicia faba and the C4 grass Anthephora pubescens also appeared to be isolated from epidermal cells. Thus guard cell isolation from cell-to-cell communication appears to be a common phenomenon. Hence, the ion fluxes required for guard cell function must occur via the apoplast.

Notes: Cell-to-cell communication has been studied in lateral branches and developing antheridia of male Chara corallina plants. The moving cytoplasm is specialized to include essentially separate ascending and descending cytoplasmic streams within the inter-nodes. The neutral line which demarcates the ascending from the descending stream is established by the divisions of the nodal initial, which gives rise to both the node and internode. The ascending stream is located beneath the first-formed node-cells and the descending stream beneath the last-formed cells. The cells destined to develop into antheridia were always located on the same side as the descending internodal stream, and thus, were derived from the cells last formed during divisions of the nodal initial. Three stages of anther idial development have been defined: (1) young antheridia from the initial division of a node-cell to the formation of an octant structure; (2) maturing antheridia where differentiation into shield, manubria and capitular cells has occurred, including antheridia where an internal cavity has formed but contains filaments of less than 32 cells; and (3) mature antheridia where filaments contain more than 32 cells and spermatid production commences. Internodal cells of branches bearing young antheridia had similar characteristics to spring branches, including high plasmalemma potential differences (-217·7±31·5mV, [K+]o 0·5 mol m−3; pH 7·6) and extensive cell-to-cell communication (frequency of intercellular transport of 6 carboxyfluorescein 86%). The small probe 6 carboxy fluorescein moved into the entire young antheridium in 100% of injections. The molecular exclusion limit for internodes and the nodal complex lay between 874 and 1678Da whereas the exclusion limit for the young antheridium was smaller (between 750 and 874Da). Internodal cells of branches bearing maturing antheridia had similarly high PDs (–221·7±40mV; [K+]o 0·5 mol m−3; pH 7·6). Cell-to-cell communication between internodes bearing maturing antheridia was extensive (frequency of intercellular transport of 6 carboxyfluorescein 100%). The shield cells were isolated from the symplast of the thallus at this stage since they did not admit 6 carboxyfluorescein. Internodal cells of branches bearing only mature antheridia showed different characteristics. Intercellular communication between internodes was restricted to a level similar to that found in winter (frequency of intercellular transport of 6 carboxyfluorescein = 57%). The mature antheridium was entirely isolated from the symplast of the thallus. A period of extensive cell-to-cell communication and high PDs in internodal cells commences in vegetative lateral branches in spring, immediately before reproductive structures are initiated. These features persist throughout summer whilst reproductive structures develop, until the antheridial filaments contain 32 or more cells (mature stage), at which point spermatid production commences and the antheridium is isolated from the thallus. In autumn, following the stage of mature antheridia, no further antheridia are initiated. Internodes are subsequently vegetative throughout winter and their lateral branches are characterized by restricted cell-to-cell communication, low internodal PDs, and little obvious growth, all features consistent with winter dormancy.

Notes: [Auszug] I have tried to demonstrate inhibition by non-pollinated carpels in tissue culture, and to extract and concentrate the growth inhibitor, using isolated receptacles in culture to assay activity. The work was carried out using the everbearing diploid Fragaria vesca semperflorens. The fruit was ...

Notes: TRANSPORT

Notes: Abstract Analysis of National Travel Survey data on the amount of walking done by 17,000 individuals has shown that people spend about twenty minutes per day travelling by foot, on average. This implies a pedestrian accident rate of about 500 accidents per hundred million miles walked, a greater rate than for car drivers but less than for motor cyclists. This paper also relates accident risk to age and sex of pedestrian, time of day, day of week, and month of year. It is further shown that, for daylight hours, the average number of pedestrian accidents is approximately proportional to the product of vehicle and pedestrian flows.

Notes: Abstract At the beginning of the 1980s, it seemed that a consensus was emerging among researchers that public transport service levels, fares or quality had a small but possibly important effect on car ownership, and that this should be taken into account for those purposes where car ownership forecasts are used for developing policy on public transport or roads. Somehow, the findings faded away, and had little effect on policy thinking or on analytical techniques. The results of six surveys carried out in South Yorkshire over the period 1972 to 1991, during which there were extreme changes in public transport policy, tend to support a prima facie case for reopening the question. At the household level, car ownership rates are shown to be more volatile than is often assumed, especially in multiple car households. This volatility provides a context within which the quality of public transport provision appears to influence both the level of car ownership and the relationship between changes in the level of car ownership and changes in public transport use.

Notes: Abstract It is argued that some of Grey's criticisms (this issue) — including those at the centre of his argument - are based on faulty logic, invalid premises, or lack of clarity about what current practice actually is. An appropriate definition of generalised cost, together with a sensitive disaggregation of major groups of the population, can help to increase the reliability of forecasts and provide a consistent underlying framework for analysis of otherwise disparate projects. Some of Grey's criticisms are more valid, however, and there is a case for some changes in current practice. This can best be done by adapting, rather than abolishing, the tool of generalised cost, since the alternatives available seem even more flawed, in terms of being either arbitrary or inconsistent.