Search Results - (Author, Cooperation:R. Loomis)

2015-04-10

Nature Publishing Group (NPG)

0028-0836

1476-4687

Biology

Chemistry and Pharmacology

Medicine

Natural Sciences in General

Physics

1399-3054

Blackwell Publishing Journal Backfiles 1879-2005

Biology

The cytokinins of developing radish roots were extracted, partially purified, and separated by thin-layer chromatography into three distinct bands of activity. One band was identified chromatographically as zeatin ribonucleotide and another was indistinguishable from a mixture of zeatin and zeatin ribonucleoside. The third band was not identified, but it was not a derivative of zeatin or of isopentenyladenine.The unidentified cytokinin had physiological properties quite different from those of the zeatin derivatives. The zeatin-based cytokinins increased in radish roots with the onset of cambial activity, and reapplication of these cytokinins to cultured primary roots stimulated cambial activity. The unidentified cytokinin became abundant only after extensive secondary thickening had occurred, and it was localized almost entirely in the xylem. It did not stimulate cambial activity in cultured roots. The evidence indicates that zeatin and its derivatives regulate cambial activity in radish, and that the unidentified cytokinin may be synthesized in the roots and transported to the shoot.

Electronic Resource

1399-3054

Blackwell Publishing Journal Backfiles 1879-2005

Biology

Electronic Resource

0025-8385

Linguistics and Literary Studies

0015-8518

Linguistics and Literary Studies

Discussion

0016-8890

German, Dutch and Scandinavian Studies

1399-3054

Blackwell Publishing Journal Backfiles 1879-2005

Biology

Several structural changes in cotton (Gossypium hirsutum L.) leaves attendant on development under conditions of water deficit were examined. Cell size was less and cell wall thickness greater in the leaves of stressed plants than in leaves of well-watered plants. A short review of the literature suggested that the lesser cell size is a fairly general observation and that it may contribute to plant resistance to moisture stress.A simple model is developed to investigate the influence of the reduction of cell size on cellular water relations. The predictions which can be drawn from simulations with this model are that smaller cells should maintain turgor to lower values of water potential than larger cells. Rather large changes in cell water relations are predicted for small changes in cell size. These effects are related principally to the changing proportion of cell water which resides in the cell wall and is external to the plasmalemma and the osmotic adjustment system. This prediction is in agreement with several observerations on the behavior of stress-hardened plants and supports the hypothesis that plants or tissues with the smaller cell size will be more tolerant of low water potential.

Electronic Resource

1399-3054

Blackwell Publishing Journal Backfiles 1879-2005

Biology

Differences among species in respiration rates in CO2-free air, in light and dark, were studied using the standard leaf chamber technique and the infrared carbon dioxide analyzer. Photosynthesis, transpiration and respiration were measured. In all species studied, rates of respiration were considerably higher in dark than in light. This effect was assumed to be due to reassimilation of the respiratory CO2. A resistance analogy model was derived to account for the apparent differences in internal recycling of CO2 among species; the differences were correlated with differences in maximum photosynthetic rates in normal air and optimal conditions (P310) and with internal resistances to CO2 diffusion (rk). Species with high P310 and low rk appear to reassimilate all the endogenous CO2, whereas other species with lower P310 and higher rk appear to reassimilate only a part of their respiratory CO2.Experiments with the photosynthetic inhibitor, 3-(3,4-dichlorophcnyl)-l,l-dimethyl urea (DCMU), indicated that species with zero respiration in CO2-free air and light release respiratory CO2 when photosynthesis is inhibited. It is concluded that the CO2 released in the presence of DCMU represents respiratory CO2 which recycles to photosynthesis under normal conditions.

Electronic Resource

0002-1482

History

Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition

0034-6551

English, American Studies

NOTES AND OBSERVATIONS

0035-8118

Romance Studies

REVIEWS

1618-2650

Springer Online Journal Archives 1860-2000

Chemistry and Pharmacology

Electronic Resource

1573-5036

Springer Online Journal Archives 1860-2000

Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition

Electronic Resource

1573-2673

Springer Online Journal Archives 1860-2000

Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics

Résumé On analyse des fissures traversantes axiales et circonférentielles au travers d'enveloppes cylindriques à l'aide d'éléments de coque épaisse reposant sur quatre points. On montre que ces éléments tiennent compte des déformations de cisaillement transversales qui soulagent certaines difficultés rencontrées dans l'utilisation de la théorie classique des coques lorsqu'elle est appliquée au voisinage de la discontinuité correspondant à l'extrémité d'une fissure. L'étude fournit les facteurs d'intensité des contraintes à l'extension et à la flexion pour les cas de pressions et de moments de flexion. On donne également la distribution des contraintes qui environnent en principe l'extrémité d'une fissure dans le cas de configurations choisies de cylindre fissuré suivant la direction circonférentielle ou axiale. On discute également la direction de la propagation de la fissure.

Abstract Axial and circumferential through cracks in cylindrical shells are analyzed using the quarter-point thick shell elements. These elements were shown to account for transverse shear deformations which alleviate several difficulties encountered in the use of classical thin shell theory when applied in the neighborhood of crack tip discontinuity. Both extensional and bending stress intensity factors for pressure and bending moment cases are given. The principle stress distribution around the crack tip for selected configurations of circumferentially and axially cracked cylinders are also given and the direction of crack propagation is discussed.

Electronic Resource