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排序方式: 共有137条查询结果,搜索用时 15 毫秒
1.
Utilization of Seed Reserves and Currently Produced Photosynthates by Embryonic Tissues of Pine Seedlings 总被引:3,自引:0,他引:3
The importance of seed reserves for growth of Pinus resinosaAit. during and shortly after seed germination was studied undercontrolled conditions. Tissues in the resting embryo were notcompletely differentiated. Many small, presumably reserve particleswere present in the embryo in addition to reserves in the megagametophyte.During seed germination, procambia in the embryo first differentiatedprotophloem 2 days after seeds were sown. The radicle beganto emerge from the seed coat at 5 days, at which time initialxylem formation was observed. Also, at approximately the sametime, primordia of primary needles were forming in the peripheralzone of the apex. Elements of the photosynthetic apparatus,including stomata and mesophyll with chloroplasts, were differentiatedfirst in the hypocotyl and then in cotyledons between 5 and8 days after seeds were sown. Photosynthetic rates of youngseedlings were correlated with rates of cotyledon expansion.During early developmental stages, reserve particles in megagametophytecells and embryo cells gradually disappeared. Surgical removalof megagametophytes at various stages of seed germination resultedin subsequent growth inhibition of the hypocotyl-radicle axis,with early removal of cotyledons suppressing most growth. Growthof primary needles appeared to be influenced indirectly by megagametophytereserves, probably by changes in amount of photosynthetic tissue.The embryo alone possessed capacity to differentiate such tissuesas primary needle primordia, stomata, and primary and secondaryvascular systems. Megagametophyte reserves appeared to contributeto growth of embryonic tissues only after the embryo itselfinitiated growth. Both current photosynthesis of seedlings andseed reserves contributed importantly to seedling development. 相似文献
2.
ROWLAND-BAMFORD AMANDA J; ALLEN L HARTWELL JR; BAKER JEFFREY T; BOOTE KEN J 《Journal of experimental botany》1990,41(12):1601-1608
The atmospheric carbon dioxide (CO2) concentration has beenrising and is predicted to reach double the present concentrationsometime during the next century. The objective of this investigationwas to determine the long-term effects of different CO2 concentrationson carbohydrate status and partitioning in rice (Oryza sativaL cv. IR-30). Rice plants were grown season-long in outdoor,naturally sunlit, environmentally controlled growth chamberswith CO2 concentrations of 160, 250, 330, 500, 660, and 900µmolCO2 mol1 air. In leaf blades, the priority between the partitioningof carbon into storage carbohydrates or into export changedwith developmental stage and CO2 concentration. During vegetativegrowth, leaf sucrose and starch concentrations increased withincreasing CO2 concentration but tended to level off above 500µmolmol1 CO2. Similarly, photosynthesis also increased withCO2 concentrations up to 500µmol mol1 and thenreached a plateau at higher concentrations. The ratio of starchto sucrose concentration was positively correlated with theCO2 concentration. At maturity, increasing CO2 concentrationresulted in an increase in total non-structural carbohydrate(TNC) concentration in leaf blades, leaf sheaths and culms.Carbohydrates that were stored in vegetative plant parts beforeheading made a smaller contribution to grain dry weight at CO2concentrations below 330µmol mol1 than for treatmentsat concentrations above ambient Increasing CO2 concentrationhad no effect on the carbohydrate concentration in the grainat maturity Key words: CO2 enrichment, starch, sucrose 相似文献
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4.
NAOI SASAKI KYOKO IWAMOTO SHINICHI NODA IZUMI KAWAKAMI 《Development, growth & differentiation》1976,18(4):457-465
Using the swimbladder of the crusian carp ( Carrasius auratus ) as an inductor, the first appearance of mesodermal competence in the presumptive ectoderm of the newt ( Triturus pyrrhogaster ) blastula was investigated. The time course of embryonic development before the gastrula stage was determined by counting the number of surface cells on a 0.25 mm line at the animal pole. Pregastrula embryos with 2–3, 4–5, 6–7 and 7–8 cells roughly correspond to those at 14, 14–12, 8–6 and 4–0 hr before the beginning of gastrulation. Using presumptive ectoderm of the early gastrula stage, 15 min was found to be the minimum time of contact necessary for the realization of induction. The reactivity of the presumptive ectoderm from pregastrula embryos was tested by 30 min contact. Presumptive ectoderm up to the 4–5 cell stage did not react to the inductor. It may become competent within the next 4–8 hr, since the ectoderm from embryos in the 6–7 cell stage was reactive. 相似文献
5.
MARCUS G. PANDY KOTARO SASAKI 《Computer methods in biomechanics and biomedical engineering》2013,16(4):265-283
A three-dimensional model of the knee is used to study ligament function during anterior-posterior (a-p) draw, axial rotation, and isometric contractions of the extensor and flexor muscles. The geometry of the model bones is based on cadaver data. The contacting surfaces of the femur and tibia are modeled as deformable; those of the femur and patella are assumed to be rigid. Twelve elastic elements are used to describe the geometry and mechanical properties of the cruciate ligaments, the collateral ligaments, and the posterior capsule. The model is actuated by thirteen musculotendinous units, each unit represented as a three-element muscle in series with tendon. The calculations show that the forces applied during a-p draw are substantially different from those applied by the muscles during activity. Principles of knee-ligament function based on the results of in vitro experiments may therefore be overstated. Knee-ligament forces during straight a-p draw are determined solely by the changing geometry of the ligaments relative to the bones: ACL force decreases with increasing flexion during anterior draw because the angle between the ACL and the tibial plateau decreases as knee flexion increases; PCL force increases with increasing flexion during posterior draw because the angle between the PCL and the tibial plateau increases. The pattern of ligament loading during activity is governed by the geometry of the muscles spanning the knee: the resultant force in the ACL during isometric knee extension is determined mainly by the changing orientation of the patellar tendon relative to the tibia in the sagittal plane; the resultant force in the PCL during isometric knee flexion is dominated by the angle at which the hamstrings meet the tibia in the sagittal plane. 相似文献
6.
Nuclear Receptors in Mosquito Vitellogenesis 总被引:1,自引:0,他引:1
RAIKHEL ALEXANDER S.; MIURA KEN; SEGRAVES WILLIAM A. 《Integrative and comparative biology》1999,39(4):722-735
Vitellogenesis in insects involves the coordinated activityof the fat body, which produces large amounts of yolk proteinprecursors (YP), and oocytes, which specifically accumulatethese proteins. The expression of YP genes is achieved throughstrict sex-, tissue-, and hormone-specific control in the femalefat body. In mosquitoes, expression of YP genes is controlledby 20-hydroxyecdysone (20E). To elucidate the role of 20E inmosquito vitellogenesis, we cloned cDNAs encoding the Aedesaegypti ecdysteroid receptor (AaEcR) and two isoforms of itsheterodimeric partner, the Ultraspiracle homologue (AaUSP).The two AaUSP isoforms differ in their A/B domains and havedistinct expression patterns. The ecdysone regulation of YPgenes likely involves products of early genes. We cloned thegene of the mosquito homologue to the Drosophila early geneE75 (AaE75) belonging to the nuclear receptor superfamily. Kineticsof AaE75 expression correlate with the expression of YP genes,suggesting that AaE75 may have a regulatory role in YP geneexpression. A second nuclear receptor superfamily member, theNGFI-B homologue AaHR38 is implicated in repression of the ecdysone-signalingpathway in the fat body of the previtellogenic female mosquitoat the state-of-arrest. Finally, three isoforms of the hepatocytenuclear factor 4 (HNF-4) homologue AaHNF-4 are differentiallyexpressed in the mosquito fat body during vitellogenesis, suggestingtheir involvement in regulating vitellogenic events in thistissue. 相似文献
7.
Abstract Dopamine has been suggested to be involved in physiological and/or behavioural changes triggered by mating in European honeybee (Apis mellifera) queens but its specific role remains unclear. In the present study, the amounts of dopamine (DA) and its metabolite, N‐acetyldopamine (NADA) are measured, in queens of various ages to clarify the association with locomotor activity. The effects of DA receptor agonist/antagonist drugs on locomotor activity are further investigated. Brain levels of DA and NADA are relatively constant during the period before mating when locomotor activity reportedly increases with age but decreases in 1‐year‐old laying queens with low locomotor activity. Reduced DA and NADA levels are also found in haemolymph of 1–3‐month‐old laying queens. When a DA receptor agonist or antagonist is injected into 6‐day‐old virgin queens, locomotor activity levels increase significantly with 2‐amino‐6,7‐dihydroxy‐1,2,3,4‐tetrahydronaphthalene (agonist), and decreased with cis(Z)‐flupenthixol (antagonist). These results suggest that DA systems are involved in the motor control of honeybee queens, and that the decline in DA levels reduces locomotor activity after mating but increased locomotor activity before mating may be independent of DA levels. 相似文献
8.
KEN‐ICHI HARANO SEIJI TANAKA MAKOTO TOKUDA HIROE YASUI SADAO WAKAMURA ATSUSHI NAGAYAMA YASUHIRO HOKAMA NORIO ARAKAKI 《Physiological Entomology》2010,35(3):287-295
The present study investigates the emergence of adult white grub beetles Dasylepida ishigakiensis Niijima et Kinoshita (Coleoptera: Scrabaeidae) from soil as well as their burrowing behaviours. ‘Standby behaviour’ (i.e. adults come to the soil surface where they expose their heads) is shown in the field and, along with emergence behaviour, is entrained by LD photocycles. These 24‐h rhythms persist after transfer to continuous light conditions for 2 days. By contrast, beetles transferred from LD photocycles to continuous dark conditions fail to show standby behaviour; thus, it appears to be manifested only in the presence of illumination. Under dark conditions, beetles emerge completely from the soil directly at the time when standby behaviour is otherwise expected to occur. Emerged adults then burrow back into the soil before dawn. Virgin and mated males, as well as virgin females, which are expected to emerge from the soil for mating on later evenings, burrow to a relatively shallow depth (<2 cm), whereas mated females burrow deeper (2–10 cm). Soil properties such as moisture, grain size, topography and temperature influence the burrowing behaviour and the depths that the beetles reach. 相似文献
9.
10.
SAMUEL K. SHEPPARD FRANCES M. COLLES NOEL D.
McCARTHY NORVAL J. C. STRACHAN IAIN D. OGDEN KEN J. FORBES JOHN F. DALLAS MARTIN C. J. MAIDEN 《Molecular ecology》2011,20(16):3484-3490
Bacterial populations can display high levels of genetic structuring but the forces that influence this are incompletely understood. Here, by combining modelling approaches with multilocus sequence data for the zoonotic pathogen Campylobacter, we investigated how ecological factors such as niche (host) separation relate to population structure. We analysed seven housekeeping genes from published C. jejuni and C. coli isolate collections from a range of food and wild animal sources as well as abiotic environments. By reconstructing genetic structure and the patterns of ancestry, we quantified C. jejuni host association, inferred ancestral populations, investigated genetic admixture in different hosts and determined the host origin of recombinant C. jejuni alleles found in hybrid C. coli lineages. Phylogenetically distinct C. jejuni lineages were associated with phylogenetically distinct wild birds. However, in the farm environment, phylogenetically distant host animals shared several C. jejuni lineages that could not be segregated according to host origin using these analyses. Furthermore, of the introgressed C. jejuni alleles found in C. coli lineages, 73% were attributed to genotypes associated with food animals. Our results are consistent with an evolutionary scenario where distinct Campylobacter lineages are associated with different host species but the ecological factors that maintain this are different in domestic animals such that phylogenetically distant animals can harbour closely related strains. 相似文献