大丰市生态农业可持续发展的回顾与思考

20世纪 80年代初 ,在全国生态经济理论研究发展时期 ,江苏省大丰市率先提出了“建设生态县(市 )”的发展战略。 1987～ 1989年在中国科学院生态环境研究中心的支持下 ,开展了“生态县 (市 )规划研究” ,并经江苏省人民政府已批准实施近 10年。1992年大丰市被国家列为全国 50个生态农业建设试点县 (市 )之一和全国 2 0个农业和农村可持续发展试验区之一 ,历时亦有 5年。回顾生态农业建设可持续发展的全过程 ,使我们清楚地看到它是农业生产力持续发展的过程 ,是构筑“三高”农业和发展无污染的安全、优质、营养食品的过程 ,也是农业生态环境工…     

Development and evolution of lateral line placodes in amphibians I. Development

Lateral line placodes are specialized regions of the ectoderm that give rise to the receptor organs of the lateral line system as well as to the sensory neurons innervating them. The development of lateral line placodes has been studied in amphibians since the early 1900s. This paper reviews these older studies and tries to integrate them with more recent findings. Lateral line placodes are probably induced in a multistep process from a panplacodal area surrounding the neural plate. The time schedule of these inductive processes has begun to be unravelled, but little is known yet about their molecular basis. Subsequent pattern formation, morphogenesis and differentiation of lateral line placodes proceeds in most respects relatively autonomously: Onset and polarity of migration of lateral line primordia, the type, spacing, size and number of receptor organs formed, as well as the patterned differentiation of different cell types occur normally even in ectopic locations. Only the pathways for migration of lateral line primordia depend on external cues. Thus, lateral line placodes act as integrated and relatively context-insensitive developmental modules.     

Web alert. Development

A selection of World Wide Web sites relevant to papers published in this issue of Current Opinion in Neurobiology.     

Transformation in Tetrahymena thermophila. Development of an inducible phenotype.

Tetrahymena thermophila transforms from a pyriform-shaped trophic form to an elongate rapidly swimming, dispersal form under the appropriate conditions of starvation [Nelsen, E. M., and DeBault, L. E. (1978). J. Protozool.25, 113–119]. The development and control of the dispersal phenotype are examined. After an initial starvation period, the cell replaces its oral structures. During oral replacement, a caudal cilium emerges at the posterior end of the cell. As oral replacement is completed, the cell becomes spindle shaped and the newly-formed oral membranelles are positioned beneath the surface of the cell with somatic ciliary rows exterior to them. The spindle-shaped cell then elongates to become the dispersal form. While the cell is developing the new oral structures, it is also drastically increasing its numbers of somatic basal bodies and cilia. The events in the transformation pathway may be arrested or reversed by feeding the cell, except that once oral replacement has begun, it is completed along with an associated streamlining of the cell. Refed cells revert to the normal vegetative phenotype, except that some shape changes persist for several hours, suggesting that they are compatible with, but independent of, growth. Blockage of protein synthesis with cycloheximide prevents all changes associated with transformation, including the shape changes and elongation of the caudal cilium. The relation between transformation and conjugation has also been examined. Less transformation takes place when mating is possible, but transformed cells may also mate.     

Development of atherosclerotic lesions in cholesterol-loaded rabbits.

To examine both of the target vessels and the optimal time of their endothelial denudation to study vascular restenosis after balloon injury in cholesterol-loaded rabbits, we made 36 atherosclerotic rabbits by feeding a hypercholesterol diet, and histologically examined the onset time and the development of atherosclerosis. Atheromatous changes were observed first after the 5th week in the thoracic aorta from the start of the diet, and then extended to the abdominal aorta, coronary artery with time. The atherosclerotic lesions in the thoracic aorta and the proximal portion of the coronary artery showed high-grade concentric intimal thickening with luminal stenosis. The abdominal aortic lesion mildly progressed. In the renal, carotid and femoral arteries, in contrast, slight atheroscleromatous changes developed during the diet period. These results suggest that the thoracic and abdominal aortas and the coronary artery would be suitable as target vessels to study vascular restenosis after balloon injury, and the endothelial denudation of these vessels should be performed between the 8th and 15th week in this diet protocol for an accurate analysis.     

Development of Stomata in Lactuca sativa L.

The structure of the epidermis on various parts of the plantof Lactuca sativa Linn. is described. Development of stomatais studied in young leaves and stems. Tognini (1897) has previouslymentioned that the stomata on stems of L. virosa develop froma meristemoid with four cutting faces but the present studypoints out that the meristemoid cuts off only two mesogene neighbouringcells and the two others are perigene.