Cell Adhesion as a Basis of Pattern in Embryonic Development

The development of the modern methodologies of cell biologyin the fifties and sixties and of molecular biology in the seventiesand eighties has led to a reductionist view of embryonic developmentthat centers on the cell and the gene as the functional unitsof development. The functional units in most inductive and morphogeneticprocesses in the embryo are not single cells, however, but ratherare collectives of interacting cells that give rise to the tissuesand organs. Can these methodological developments reconcilea molecular analysis with the fact that form arises epigeneticallyfrom the increasing number of embryonic cells during development?To answer this question one must link genetic regulation tomechanochemical processes that coordinate cell division, cellmovement and cell death. Recent studies of cell adhesion suggestthat one such link is provided by cell adhesion molecules (CAMs)that mediate cell-cell binding. These studies suggest that CAMsare involved in defining cell collectives and their bordersas they interact during inductive events in morphogenesis. AlthoughCAMs cannot be considered the "cause" of induction, they playkey roles among the complex causal chains of inductive interactionsinvolving hormones and growth-factors, extracellular matrixcomponents and cellular receptors. We provide here a brief summaryof modern developments in the field centered about the functionof CAMs in morphogenesis and using recent experimental resultsin the developing feather as a paradigmatic example.     

Growth and Sucrose Metabolism of Carrot Callus Strains with Normal and Low Acid Invertase Activity

The properties of two strains of carrot (Daucus carota) callus are presented. One has a very low acid invertase activity which is accompanied by differences in morphology and metabolic rate, but not in growth rate. We conclude that one of the main functions of plant acid invertases is in controlling the levels of sugars which, by interaction with hormones, affect differentiation, both morphological and biochemical. The effect of tris on sucrose metabolizing enzymes, and the cause of the “sucrose effect” are considered.     

Permeability of Sugar-cane Chloroplasts to Sucrose

The Sucrose permeability of chloroplast-bounding membranes wasmeasured by three different methods. These gave similar valuesand suggested that the chloroplast membrane was fairly rapidlypermeable to sucrose. The chloroplast membranes were found tobe about 10⁴-fold more permeable to sucrose efflux than carrotcallus cells.     

MONITORING SCALING DRIFT FOR HEDONIC CATEGORY SCALES

Judges on anti-nausea medication, used hedonic scales to assess a set of foods and beverages on two occasions, initially on beginning a treatment with anti-nausea medication and then four weeks later. To detect the possibility that changes in hedonic scores for the foods and beverages may be caused not by changes in liking but by 'scaling drift': changes in the use of the scale, control stimuli were also assessed. These control stimuli were sets of stimuli to be assessed for intensity and a set to be assessed for liking. These latter stimuli were a class of stimuli that were unlikely to be liked to a different extent on the two testing occasions. The lack of change in the control stimuli and the change in the hedonic scores for the foods and beverages suggested that the latter was due to changes in liking for the foods and beverages rather than 'scaling drift'.