谷斑皮蠹在云南适生性初步研究

本文报道了在瑞丽、畹町、昆明的仓储条件下用小麦、绿豆、花生饲养谷斑皮蠹,观察其生长繁殖,把仓储与气象的温湿度对照分析得出:当仓温连续5-6个月在25℃时有利该虫繁殖生存;仓温连续5个月在21.8-23℃时该虫可生存很长一段时间但有时可化蛹完成一世代,有时仅脱皮不化蛹完不成一世代.三种饲料中繁殖倍数为小麦>绿豆>花生.笔者认为:探讨该虫在一地区能否生存和为害,除仓储温湿度外尚需考虑天敌、虫种间竞争关系诸问题.     

Cotton root growth as affected by changes in soil water distribution and their impact on plant tolerance to drought

The capability of mature cotton plants (Gossypium hirsutum L.) to adjust to progressive drying of their root zone by promoting root growth to adjacent wetted zones, and the implications of this process on irrigation design were investigated. Field grown plants that developed shallow root systems in response to a drip irrigation management of daily, surface soil wettings were exposed 85 days after emergence (DAE), while in the flowering stage, to a sudden change in water distribution in the form of deep soil wetting (DSW) followed by termination of irrigation. The shallow rooted plants (SRP) failed to respond to further surface soil wetting and the progressive drying of the profile by rapid root growth to the deeper-wetted zones; consequently, the SRP suffered from water deficiency for at least two weeks, evidenced by a gradual decrease in their leaf water potential (L_w). Potted plants responded similarly. Daily irrigations of the pot surface with water amounts similar to those lost by evapotranspiration led to the development of a system in which most of the roots and available water became concentrated at the pot's upper section. A transition to irrigation from the bottom of the pot led to a reversed soil-water content gradient and failed to promote rapid root spreading to the deeper-wetted layers, in spite of the accelerated drying of the upper zone. The slow deepening of the root system was accompanied by water-stress symptoms as indicated by a considerable reduction in dry matter production. The root shoot ratio in these plants was not much greater than in non-stressed plants in which the surface wetting was continued. This indicated that preferential root growth relative to the shoot did not occur in response to the progressive drying of the shallow root zone. Rewetting of the root zone after a long period of soil water deficiency failed to promote rapid recovery of the root system in the form of root regrowth in this zone. It was concluded that the capability of mature cotton plant roots to adjust their growth to large changes in water distribution in the soil, is slow and that this should be taken into account when determining an irrigation regime in which the depth at which water is applied is changed during the growing season.Contribution from the Agricultural Research Organization, Volcani Center, Bet Dagan, Israel; No. 343-E, 1992 series     

Radar soundings of the ionosphere of Mars

We report the first radar soundings of the ionosphere of Mars with the MARSIS (Mars Advanced Radar for Subsurface and Ionosphere Sounding) instrument on board the orbiting Mars Express spacecraft. Several types of ionospheric echoes are observed, ranging from vertical echoes caused by specular reflection from the horizontally stratified ionosphere to a wide variety of oblique and diffuse echoes. The oblique echoes are believed to arise mainly from ionospheric structures associated with the complex crustal magnetic fields of Mars. Echoes at the electron plasma frequency and the cyclotron period also provide measurements of the local electron density and magnetic field strength.     

Mars north polar deposits: stratigraphy, age, and geodynamical response

The Shallow Radar (SHARAD) on the Mars Reconnaissance Orbiter has imaged the internal stratigraphy of the north polar layered deposits of Mars. Radar reflections within the deposits reveal a laterally continuous deposition of layers, which typically consist of four packets of finely spaced reflectors separated by homogeneous interpacket regions of nearly pure ice. The packet/interpacket structure can be explained by approximately million-year periodicities in Mars' obliquity or orbital eccentricity. The observed approximately 100-meter maximum deflection of the underlying substrate in response to the ice load implies that the present-day thickness of an equilibrium elastic lithosphere is greater than 300 kilometers. Alternatively, the response to the load may be in a transient state controlled by mantle viscosity. Both scenarios probably require that Mars has a subchondritic abundance of heat-producing elements.     

Testicular morphology in rats vasectomized as adults

Vasectomy was performed on 63 rats at age 81 to 105 days. Examination 28 to 58 days later disclosed no significant reductions in testis size with respect to preoperative testis length and to testis length and weight in unoperated controls. The fact that the minimal atrophy observed was primarily left-sided sugested that these effects were artifacts of the procedure or systemic left-right differences in the animals.     

Establishment of shallow and restricted root systems in cotton and its impact on plant response to irrigation

Summary The effects of frequent and shallow soil wetting by surface drip irrigation on root growth, morphology, and location, and their impact on plant sensitivity to irrigation management were studied in cotton (Gossypium hirsutum L.). Daily drip irrigation, which wetted the 0 to 40-cm soil depth, encouraged root development mainly around the drippers. Water extraction took place mostly from 0 to 20 cm below the drippers, where the roots were concentrated. Shallowness of root growth was not altered by the expansion and deepening of the wetted soil zone which resulted from an increase in amount of irrigation water. The shallow and restricted root system was characterized by a high fraction of thin roots (less than 1 mm dia.) which comprised almost 90% of the root dry matter. Root proximity to the drippers and the limited amount of water in the rooted soil led to a sensitive and quick response of the plants to small amounts of irrigation. A supply of 1.0 mm H₂O given at midday to 70 day-old plants resulted in a leaf water potential (L _w) increase from –1.64 to –1.32 MPa over a 20-min period. This amount of irrigation comprised 15% of the average daily quantity. A 24 h delay in irrigation to 80 dayold plants was enough to decrease L _w from –1.41 to –2.42 MPa. This decrease was caused by a soil water deficit of less than 6 mm H₂O. Extending the irrigation delay to 72 h affected yield and earliness, although the deficient amount of water was supplied over the several days after the treatment. A strong response to minor, but continuous, differences in the daily irrigation amount was detected. Differences in irrigation of less than 1 mm H₂O per day applied during the whole growth season substantially affected L _w, yield and earliness. It was concluded that the establishment of a shallow and restricted root system resulted in strong dependence of the plants on frequent and sufficient supply of water, and temporary minor changes in irrigation affected plant water status and productivity.     

Evidence of soft-mode quantum phase transitions in electron double layers

Inelastic light scattering by low-energy spin-excitations reveals three distinct configurations of spin of electron double layers in gallium arsenide quantum wells at even-integer quantum Hall states. The transformations among these spin states appear as quantum phase transitions driven by the interplay between Coulomb interactions and Zeeman splittings. One of the transformations correlates with the emergence of a spin-flip intersubband excitation at vanishingly low energy and provides direct evidence of a link between quantum phase transitions and soft collective excitations in a two-dimensional electron system.     

Lactation Biology Symposium: circadian clocks as mediators of the homeorhetic response to lactation

The transition from pregnancy to lactation is the most stressful period in the life of a cow. During this transition, homeorhetic adaptations are coordinated across almost every organ and are marked by changes in hormones and metabolism to accommodate the increased energetic demands of lactation. Recent data from our laboratory showed that changes in circadian clocks occur in multiple tissues during the transition period in rats and indicate that the circadian system coordinates changes in the physiology of the dam needed to support lactation. Circadian rhythms coordinate the timing of physiological processes and synchronize these processes with the environment of the animal. Circadian rhythms are generated by molecular circadian clocks located in the hypothalamus (the master clock) and peripherally in every organ of the body. The master clock receives environmental and physiological cues and, in turn, synchronizes internal physiology by coordinating endocrine rhythms and metabolism through peripheral clocks. The effect of the circadian clock on lactation may be inferred by the photoperiod effect on milk production, which is accompanied by coordinated changes in the endocrine system and metabolic capacity of the dam to respond to changes in day length. We have shown that bovine mammary epithelial cells possess a functional clock that can be synchronized by external stimuli, and the expression of the aryl hydrocarbon receptor nuclear translocator-like gene, a positive limb of the core clock, is responsive to prolactin in bovine mammary explants. Others showed that 7% of genes expressed in breasts of lactating women had circadian patterns of expression, and we report that the diurnal variation of composition of bovine milk is associated with changes in expression of mammary core clock genes. Together these studies indicate that the circadian system coordinates the metabolic and hormonal changes needed to initiate and sustain lactation, and we believe that the capacity of the dam to produce milk and cope with metabolic stresses in early lactation is related to her ability to set circadian rhythms during the transition period.     

Experiments in chicory growing under Israel condition

Sommaire Les auteurs donnent un aperçu des essais faits avec six variétés de Cichorium Intybus cultivées et utilisées comme fourrage, comme plante pour pâturages et comme remplaçent le café. L'étude se rapporte aux conditions de la culture et des propriétés agronomiques de la Chicorée, la possibilité de sélection d'une variété spécialement adaptée aux conditions de l'Israel. Biologie, constitution chimique, fûmage etc. fûrent étudiés et les resultats obtenus démontrés sur 15 tableaux.