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Shea butter tree.

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Botany↗
PubMedDate not supplied

On the definition of cannabinoids: botanical? chemical? pharmacological?

Cannabinoids (or presumed synonyms such as cannabinols or cannabis-like agents) have been variously defined in botanical, chemical, or pharmacological terms, with unfortunate consequences. Botanical definitions include inactive substances such as cannabigerol, as well as alkaloids and other secondary constituents of Cannabis sativa, but exclude synthetics such as levonantradol and nabilone. Chemical definitions include inactive close analogs of THC but exclude a growing number of substances structurally remote from THC that share its actions. Pharmacological definitions have depended on relatively nonspecific or vague behavioral endpoints. However, animal testing methodology has recently been developed that can identify and quantify agents that share THC's unique subjective effects. To avoid preexisting ambiquity in the word cannabinoids, the term cannabimimetics has been coined to include all such agents, regardless of origin or structure. Such a classification emphasizes research toward improved biological selectivity and therapeutic advance. While no totally noncannabimimetic agents with potent analgesic effects have yet been identified among derivatives of THC, selectivity has been uncovered for levonantradol, HHC (racemic-9-nor, 9-beta-OH-hexahydrocannabinol) and several structurally related compounds.

Animals↗
PubMed1989

Freeze-fracture: a personal history.

The sequence of events leading to the development of freeze-fracture replication is described. Subsequent developments discussed include complementary replicas, replica interpretation with stereo micrograph and reversal negatives, replica reinforcement, and control of resistance evaporation.

Botany↗
PubMed1996

The history of tissue tension.

In recent years the phenomenon of tissue tension and its functional connection to elongation growth has regained much interest. In the present study we reconstruct older models of mechanical inhomogenities in growing plant organs, in order to establish an accurate historical background for the current discussion. We focus on the iatromechanic model developed in Stephen Hales' Vegetable Staticks, Wilhelm Hofmeister's mechanical model of negative geotropism, Julius Sachs' explanation of the development of tissue tension, and the differential-auxin-response-hypothesis by Kenneth Thimann and Charles Schneider. Each of these models is considered in the context of its respective historic and theoretical environment. In particular, the dependency of the biomechanical hypotheses on the cell theory and the hormone concept is discussed. We arrive at the conclusion that the historical development until the middle of our century is adequately described as a development towards more detailed explanations of how differential tensions are established during elongation growth in plant organs. Then we compare with the older models the structure of more recent criticism of hormonal theories of tropic curvature, and particularly the epidermal-growth-control hypothesis of Ulrich Kutschera. In contrast to the more elaborate of the older hypotheses, the recent models do not attempt an explanation of differential tensions, but instead focus on mechanical processes in organs, in which tissue tension already exists. Some conceptual implications of this discrepancy, which apparently were overlooked in the recent discussion, are briefly evaluated.

Biophysics↗
PubMed1997

Categorization and reasoning among tree experts: do all roads lead to Rome?

To what degree do conceptual systems reflect universal patterns of featural covariation in the world (similarity) or universal organizing principles of mind, and to what degree do they reflect specific goals, theories, and beliefs of the categorizer? This question was addressed in experiments concerned with categorization and reasoning among different types of tree experts (e.g., taxonomists, landscape workers, parks maintenance personnel). The results show an intriguing pattern of similarities and differences. Differences in sorting between taxonomists and maintenance workers reflect differences in weighting of morphological features. Landscape workers, in contrast, sort trees into goal-derived categories based on utilitarian concerns. These sorting patterns carry over into category-based reasoning for the taxonomists and maintenance personnel but not the landscape workers. These generalizations interact with taxonomic rank and suggest that the genus (or folk generic) level is relatively and in some cases absolutely privileged. Implications of these findings for theories of categorization are discussed.

Adult↗
PubMed1994

Genetic analyses of signalling in flower development using Arabidopsis.

Flower development can be divided into four major steps: phase transition from vegetative to reproductive growth, formation of inflorescence meristem, formation and identity determination of floral organs, and growth and maturation of floral organs. Intercellular and intracellular signalling mechanisms must have important roles in each step of flower development, because it requires cell division, cell growth, and cell differentiation in a concerted fashion. Molecular genetic analysis of the process has started by isolation of a series of mutants with unusual flowering time, with aberrant structure in inflorescence and in flowers, and with no self-fertilization. At present more than 60 genes are identified from Arabidopsis thaliana and some of them have cloned. Although the information is still limited, several types of signalling systems are revealed. In this review, we summarize the present genetic aspects of the signalling network underlying the processes of flower development.

Arabidopsis↗