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121.
At the end of the spring 1987 growing season, the mycoparasite Sporidesmium sclerotivorum was applied at 0, 0.2, 2 or 20 kg ha‐1 to lettuce plants infected with Sclerotinia minor. Disease incidence was monitored in the same plots for five subsequent crops (three fall and two spring crops) without additional application of either pathogen or mycoparasite. Logistic growth curves were fitted to the data to describe disease progression over time for each inoculum level within each of the five crops. Within each crop, increasing the quantity of mycoparasite inoculum resulted in positive horizontal displacement of the curve with respect to time. As quantities of inoculum of S. sclerotivorum increased, inflection points of the disease progress curves increased at a decreasing rate. Thus, additional mycoparasite inoculum resulted in ever‐smaller increases in inflection point, and after a certain threshold level of mycoparasite inoculum (< 0.2 kg ha‐1), increases in inflection point did not result in meaningful increases in harvestable lettuce. Maximum rates of disease increase were not different among the treatments within each crop, but were different between crops. Maximum rates of disease increase averaged 3.4, 3.4, 2.1, 3.6 and 1.5% day‐1 for the fall 1987, spring 1988, fall 1988, spring 1989, and fall 1989, respectively. At all inoculum levels, the fall epidemics began later after planting than the spring epidemics.  相似文献   
122.
1. Initiation of subsynaptic sarcolemmal specialization and expression of different molecular forms of AChE were studied in fast extensor digitorum longus (EDL) and slow soleus (SOL) muscle of the rat under different experimental conditions in order to understand better the interplay of neural influences with intrinsic regulatory mechanisms of muscle cells. 2. Former junctional sarcolemma still accumulated AChE and continued to differentiate morphologically for at least 3 weeks after early postnatal denervation of EDL and SOL muscles. In noninnervated regenerating muscles, postsynaptic-like sarcolemmal specializations with AChE appeared (a) in the former junctional region, possibly induced by a substance in the former junctional basal lamina, and (b) in circumscribed areas along the whole length of myotubes. Therefore, the muscle cells seem to be able to produce a postsynaptic organization guiding substance, located in the basal lamina. The nerve may enhance the production or accumulation of this substance at the site of the future motor end plate. 3. Significant differences in the patterns of AChE molecular forms in EDL and SOL muscles arise between day 4 and day 10 after birth. The developmental process of downregulation of the asymmetric AChE forms, eliminating them extrajunctionally in the EDL, is less efficient in the SOL. The presence of these AChE forms in the extrajunctional regions of the SOL correlates with the ability to accumulate AChE in myotendinous junctions. The typical distribution of the asymmetric AChE forms in the EDL and SOL is maintained for at least 3 weeks after muscle denervation. 4. Different patterns of AChE molecular forms were observed in noninnervated EDL and SOL muscles regenerating in situ. In innervated regenerates, patterns of AChE molecular forms typical for mature muscles were instituted during the first week after reinnervation. 5. These results are consistent with the hypothesis that intrinsic differences between slow and fast muscle fibers, concerning the response of their AChE regulating mechanism to neural influences, may contribute to different AChE expression in fast and slow muscles, in addition to the influence of different stimulation patterns.  相似文献   
123.
Summary The development of acellular extrinsic fiber cementum (AEFC) has never before been studied in human teeth. We have therefore examined the initiation of AEFC in the form of a collagenous fiber fringe and its attachment to the underlying dentinal matrix, in precisely selected, erupting human premolars with roots developed to 50%–60% of their final length. Freshly extracted teeth were prefixed in Karnovsky's fixative, decalcified in EDTA and subdivided into about 10 blocks each, cut from the mesial and distal root surfaces, vertical to and along the root axis. The blocks were postfixed in osmium tetroxide, embedded in Epon and cut for light- and electron-microscopic investigation. Starting at the advancing edge of the root, within a region extending about 1 mm coronal to this edge, fibroblast-like cells were seen closely covering the external root surface. Along the first 100 m from the root edge, these cells extended cytoplasmic processes and contacted the dentinal collagen fibrils. Between these cells and the dentinal matrix, new collagen fibrils and very short collagen fibers gradually developed. Within the second 100 m from the root edge, this resulted in the formation of a cell-fiber fringe network. Newly formed fibers of the fringe were directly attached to the non-mineralized matrix containing dentinal collagen fibrils and could be distinguished from the latter by differences in fibril orientation. During the process of dentin mineralization, the transitional zone between the fiber-fringe base and the dentinal matrix, i.e., the future dentino-cemental junction, also mineralized. It is suggested that this fiber fringe is the base of AEFC, which later increases in thickness by fiber extension and subsequent mineralization.Abbreviations AEFC acellular extrinsic fiber cementum - AIFC acellular intrinsic fiber cementum - CIFC cellular intrinsic fiber cementum - CMSC cellular mixed stratified cementum - ARE advancing root edge - CP cytoplasmic process - D dentin - DCJ dentinocemental junction - E enamel - EBL external basal lamina - EC epithelial cell - EDTA ethylene diaminetetraacetic acid - ERM epithelial rests of Malassez - FF fiber fringe - HRS Hertwig's epithelial root sheath - IBL internal basal lamina - MD mineralized dentin - NMD non-mineralized dentin - OB odontoblast - PD predentin - PL periodontal ligament  相似文献   
124.
Summary To study the three-dimensional structure of tight junction fibrils, the epithelia of the jejunum and epididymis of adult mice were examined by the freezefracture technique in unfixed and in aldehyde-fixed specimens. The fibrils have a stronger affinity for the protoplasmic (P) face of the lipid bilayer in fixed material, and for the external (E) face in unfixed and rapidly frozen material. Therefore we can observe the fibrils both from the outside and inside of the cell. Fibrils appearing on the P-face are smoothly contoured ridges and rows of hemispherical particles, while those appearing on the E-face are exclusively rows of hemispherical particles. Based on these observations, we wish to propose a new fibril model for the tight junction. There are two distinctive types of junctional elements. One type is composed of a smooth and continuous strand in the external view of the cell, but is studded with hemispherical bulgings in its internal view. This type will be referred to as the continuous type. The other type is bead-like, and will be referred to as the particle type. The relative proportion of these two types of elements appearing within a tight junction network differs among tissues.  相似文献   
125.
Summary The effect of pH was tested on the junction between crayfish lateral axons. By means of a glass capillary inserted into one of the axons, one side of the nunction was perfused with solutions of known pH while the junctional resistance,R j, was monitored. Integrity of the gap junction was checked electron microscopically.R j remained unchanged when the pH of the perfusate was lowered from 7.1 to 6.0. However, when the pH of the unperfused side of the junction was lowered by substituting acetate for chloride in the external solution,R j rose, attesting to the integrity of the junction and its capacity to uncouple in the perfused state. We suggest that H+ does not affect the junctional channels directly, but acts through an intermediary which is inactivated or removed by the perfusion.  相似文献   
126.
Summary The gap junction morphology was quantified in freeze-fracture replicas prepared from rat auricles that had been either quickly frozen at 6 K or chemically fixed by glutaraldehyde, in a state of normal cell-to-cell conduction or in a state of electrical uncoupling. The general appearance of the gap junctions was similar after both preparative procedures. A quantitative analysis of three gap junctional dimensions provided the following measurements in the quickly frozen conducting auricles (mean±sd): (a) P-face particles' diameter 8.27±0.74 nm (n =5709), (b) P-face particles' center-to-center distance 10.78±2.12 nm (n=4800), and (c) E-face pits' distance 9.99±2.19 nm (n=1600). Corresponding values obtained from chemically fixed tissues were decreased by about 3% for the particle's diameter and about 5% for the particles' and pits' distances. Electrical uncoupling by the action of either 1 mM 2–4-dinitrophenol (DNP), or 3.5 mMn-Heptan-1-ol (heptanol), induced a decrease of the particle's diameter, which amounted to –0.69±0.01 nm (mean ±se) in the quickly frozen preparations and –0.71±0.01 nm in the chemically fixed ones. The particles' distance was decreased by –0.96±0.04 nm in the quickly frozen samples and by –0.90 ±0.03 nm in the chemically fixed ones and the E-face pits' distance was similarly reduced. All differences were statistically significant (P<0.001 for all dimensions). Electrical recoupling after the heptanol effect promoted a return of these gap junctional dimensions towards normal values, which was about 50% complete within 20 min. It is concluded that very similar morphological alterations of the gap junctional structure are induced in the mammalian heart by different treatments promoting electrical uncoupling and that these conformational changes appear independently of the preparative procedure. The suggestion that the observed decrease of the particles' diameter is genuinely related to the closing mechanism of the unit cell-to-cell channel set in thei centers is thus confirmed.  相似文献   
127.
Summary The viralsrc gene downregulates junctional communication, closing cell-to-cell membrane channels presumably by way of the phosphoinositide signal route. We show that TMB-8 [8-N, N-(diethylamino) octyl-3,4,5-trimethoxybenzoate] counteracts this downregulation in cells transformed by temperature-sensitive mutant Rous sarcoma virus: TMB-8 (36–72 m) raises junctional permeability when applied during activity ofsrc protein kinase, i.e., at steady permissive temperature; and TMB-8 inhibits the fall of junctional permeability, when the activity ofsrc protein kinase gets turned on. TMB-8 also (reversibly) inhibits the growth of the cells at permissive temperature and reverses the morphological changes associated with transformation. The morphological reversal lags several hours behind the junctional-permeability reversal. Communication recovers within a few minutes when the activity of thesrc protein kinase is turned off (in absence of TMB-8). Sodium orthovanadate (20 m) prevents this recovery, but it has no major effect on junctional permeability on its own. We discuss possible modes of action of these agents on critical stages of the signal route, related to intracellular Ca2+ and protein kinase C.  相似文献   
128.
用电镜观察了经受诱导作用之后胚胎细胞的冷冻蚀刻复型膜。和未经诱导作用的对照组比较,早期和中期神经胚的神经上皮细胞以及经过豚鼠骨髓粗提液(BME)——一种有效的异源中胚层诱导物——处理过的早期原肠胚外胚层,它们的间隙连接都处于活跃的动态状态。用图像分析仪测得的间隙连接连接子的排列密度,指出经受过诱导作用的三组分别和未经受诱导作用的对照组比较,计算求出P值,神经上皮两组和对照组的差别为非常显著,BME处理过的细胞和对照组的差别为显著。结合对照组与诱导后胚胎细胞间隙连接连接子的变化讨论了它们在信息传递上可能起的作用。  相似文献   
129.
Summary The wing discs of the temperature-sensitiveDrosophila mutantl(3)c43 hs1 become hyperplastic when larvae are reared at the restrictive temperature of 25° C or above (Martin et al. 1977). We have previously shown that reductions in gap junctions are correlated with the hyperplasia (Ryerse and Nagel 1984a). We report here that reductions in gap junction surface density, number and percent of the lateral plasma membrane area precede the onset of tissue hyperplasia as defined by the gross appearance of tissue overgrowth in the wing pouch and an increase in cell number. Gap junction reductions begin soon after temperature upshift and become significantly different from non-shifted controls by 16 h. Direct cell counts indicate that there is no difference in the total number of cells in experimental vs control discs until after 16 h when the 28° C discs begin to grow rapidly with a cell doubling time of about 6 h as compared with about 13 h for the 20°C controls. The finding that gap junction reductions precede the onset of tissue hyperplasia is consistent with the idea that gap junctions play a regulatory role in growth control and pattern formation and strengthens our hypothesis (Ryerse and Nagel 1984b) that a minimum number and a specific distribution of gap junctions are required for normal development.  相似文献   
130.
Stylet ultrastructure of five Xiphinema, four Longidorus, and three Californidorus species was compared by scanning electron microscopy. Morphological differences were seen in the odontophores and odontostyle bases between the genera and some of the species. All Xiphinema studied had well-developed odontophore flanges; the Longidorus species lacked flanges, except for weakly developed ones in L. diadecturus; and none of the Californidorus had flanges. Three sinuses were present in the odontophores of all species. The sinuses varied in length depending upon species. In Xiphinema and Californidorus the odontostyle bases had distinct overlapping collars, but in Longidorus the collars were absent except for L. diadecturus. The odontostyle-odontophore junction from a lateral view appeared as a slanted transverse line in all the species, but in a dorsal view of Xiphinema and Californidorus it was V-shaped. Dorsal longitudinal seams of the odontostyle and odontophore were observed in all the species. The dorsally located odontostyle aperture was ca. 1 μm from the anterior end in all species, except in one Longidorus sp. it was ca. 4 μm from the end.  相似文献   
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