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21.
Criconemella xenoplax, Fusarium solani, and F. oxysporum caused necrosis of Nemaguard peach feeder roots in greenhouse tests. Root necrosis was more extensive in the presence of either fungus than wtih C. xenoplax alone. Shoot growth and plant height were less for plants inoculated with F. oxysporum or F. solani than for plants inoculated with the fungi plus C. xenoplax. Neither synergistic nor additive effects on root necrosis or plant growth occurred between C. xenoplax and the fungal pathogens. 相似文献
22.
Phenamiphos (6.7 kg a.i./ha) was applied via an irrigation simulator to squash at planting (AP) and 2 weeks after planting (PP), and to corn AP and 1 week PP to manage root-knot nematodes (Meloidogyne incognita). The nematicide was applied with 0.25, 0.64, 1.27, and 1.91 cm surface water/ ha to a Lakeland sand in which the soil moisture was at or near field capacity. Based on efficacy and crop response, no additional benefits resulted when phenamiphos was applied in volumes of water greater than 0.25 crn/ha. The cost of applying each 0.25 cm of water over a hectare is approximately $1.08, or a 92% reduction in nematicide application cost over conventional methods ($13.50/ha). Low root-gall indices and high yields from squash and corn indicate more effective nematode management when phenamiphos was applied AP rather than PP. Results from this method of applying phenamiphos suggest that certain nematicides could be used as salvage alternatives when nematodes are detected in crops soon after planting. For multiple-pest management, nematicides, other compatible biocides, and fertilizers could be applied simultaneously with sprinkler irrigation. 相似文献
23.
Claudio Nicolini Andrew S. Belmont Antonietta Martelli 《Cell biochemistry and biophysics》1986,8(2):103-117
Using HeLa S-3 cells synchronized by selective detachment, in this paper we report a parallel study of nuclear morphology
and autoradiography grain patterns between middle G1 and middle S phases: Our results show two distinct [3H]-thymidine labeling patterns. The first “peripheral” labeling pattern has a characteristic nuclear size distribution, in
contrast to the heterogeneous and varying size distributions of Feulgen-stained nuclei, and apparently is characteristic of
very early S phase. The sizes of the second labeling pattern—homogeneous or inhomogeneous grain distribution throughout the
nucleus—are equal or larger than the first and vary with S phase progression. Together, the corresponding nuclear sizes of
the labeled nuclei represent the larger extreme of nuclear areas, and the labeling index closely parallels the fraction of
nuclei with areas larger than the minimum size of the labeled nuclei. These results suggest a characteristic nuclear size
(reflecting unique intranuclear DNA distribution) as a necessary, if not sufficient, requirement for S phase initiation. Parallel
experimentation with rat liver cells—synchronized in vivo by partial hepatectomy and analyzed by thin section autoradiography—confirms
the existence of a peripheral labeling pattern in both the very early part and the very late part of S phase, which reconciles
our data with previous results and points to the fact that both initiation and termination sites for DNA replication are near
the nuclear periphery. 相似文献
24.
25.
6-C-α-l-Arabinopyranosyl- and furanosylacacetins have been synthesized. They are isomerized by short acid treatment to give a mixture of the four anomer/ring size combinations without any Wessely-Moser isomerization. In the same conditions molludistin (8-C-α-l-arabinopyranosylgenkwanin) led only to a mixture of molludistin and 8-C-α-l-arabinofuranosylgenkwanin. This is the first demonstration of ring sugar isomerization in C-glycosylflavones. In usual solvent systems, α-anomers are easily separated from β-anomers, whereas corresponding pyranosyl and furanosyl anomers are not. However, they are easily separated after permethylation and characteristic features are found in the mass spectra of PM 6-C-arabinofuranosyl isomers. 相似文献
26.
Tsuneyoshi Kuroiwa 《Journal of plant research》1989,102(2):291-329
It has been established that organelles, such as mitochondria and plastids, contain organelle-specific DNA and arise from
the division of pre-existing organelles (e.g., Possingham and Lawrence, 1983). We propose that organelle DNAs, such as mitochondrial
DNA and plastid DNA are not naked in organellesin situ but are organized in each case to form an “organelle nucleus” with basic proteins (Kuroiwa, 1982). The concept of organelle
nuclei has changed our ideas about the division of organelles. Thus, the process of organelle division must be composed of
two main events: division of the organelle nucleus and organellekinesis (division of the other components of the mitochondrion
or plastid). The latter term has been adopted as an appropriate analogue of cytokinesis.
We were the first to identify the plastid-dividing ring (PD-ring), which is located in the cytoplasm close to the outer envelope
membrane at the constricted isthmus of dividing chloroplasts in the red algaCyanidium caldirum. The PD-ring is about 60 nm in width and 25 nm in thickness, and is a circular bundle of actin-like, fine filaments, each
about 4–5 nm in diameter. Since cytochalasin B, an inhibitor of polymerization of actin filaments, inhibits the formation
of the PD-ring and, thus, prevents subsequent division of chloroplasts, the PD-ring is thought to be a structure that is essential
for the division of plastids (plastidkinesis).
The behavior of the PD-ring during a cycle of chloroplast division can be classified into the following four stages on the
basis of morphological and temporal differences. The chloroplast growth stage: the small, spherical chloroplast increases
in volume and becomes a football-like structure, while the PD-ring from the previous division disappears. Formation of the
PD-ring: the somewhat electron-dense body (see below) is fragmented into many, somewhat electron-dense granules, which are
aligned along the equatorial region of the chloroplast and fine filaments are formed from the somewhat electron-dense granules
in the equatorial region. The fine filaments of the PD-ring align themselves according to the longest axis of their overall
domain, i.e., circumferentially. Contraction stage: a bundle of fine filaments begins to contract and generates a deep furrow.
Conversion stage: after chloroplast division, the remnants of the PD-ring are converted into somewhat electron-dense bodies.
Similar events occur during the second cycle of chloroplast division. Since similar structures are observed extensively in
the plastids of algae, moss and higher plants, the PD-ring appears to be an essential structure for the division of plastids
in plants. 相似文献
27.
Joakim Galli Urban Lendahl Gabrielle Paulsson Christer Ericsson Tomas Bergman Mats Carlquist Lars Wieslander 《Journal of molecular evolution》1990,31(1):40-50
Summary We describe the structure of a gene expressed in the salivary gland cells of the dipteranChironomus tentans and show that it encodes 1 of the approximately 15 secretory proteins exported by the gland cells. This sp115,140 gene consists of approximately 65 copies of a 42-bp sequence in a central uninterrupted core block, surrounded by short nonrepetitive regions. The repeats within the gene are highly similar to each other, but divergent repeats are present in a pattern which suggests that the repeat structure has been remodeled during evolution. The 42-bp repeat in the gene is a simple variant of the more complex repeat unit present in the Balbiani ring genes, encoding four of the other secretory proteins. The structure of the sp115,140 gene suggests that related repeat structures have evolved from a common origin and resulted in the set of genes whose secretory proteins interact in the assembly of the secreted protein fibers. 相似文献
28.
The palm weevil, Rhynchophorus palmarum (L.), was collected in cocoons from red ring-diseased coconut palms (Cocos nucifera L.) in Trinidad and Tobago. Juveniles of five species of nematodes were extracted from the genitalia and macerated bodies of newly emerged adults of the palm weevil: Rhadinaphelenchus cocophilus (Cobb) Goodey (the red ring nematode), Teratorhabditis sp., Diplogasteritus sp., Mononchoides sp., and Bursaphelenchus sp. Over 90% of newly emerged weevil females and males were infested internally with red ring nematode juveniles, and over 47% of the weevils contained more than 1,000 red ring nematodes each. There was no significant correlation between weevil body length and the number of red ring nematodes carried internally by each weevil. Teratorhabditis sp. and Diplogasteritus sp. were extracted from over 50% of the palm weevils, and Monochoides sp. and Bursaphelenchus sp. were found in a small proportion of the weevils. Field-collected adult weevils were also internally and externally infested with a Rhabditis sp., which was not observed in or on weevils allowed to emerge from field-collected cocoons. 相似文献
29.
Abstract.
- 1 Seasonal population growth rates for the pea aphid, Acyrthosiphon pisum Harris, were determined in three different host plant habitats; alfalfa, Medicago sativa (L.), clover, Trifolium pratense (L.), and peas, Pisum sativum (L.); over four years and eight places. It was possible to estimate a common intrinsic rate of increase for each host plant habitat.
- 2 An analysis of the relative influence of temporal, spatial and host plant habitat variation showed that the host plant habitat was most important in determining the growth rates of the populations, both in rate of build-up and decline.
- 3 Patterns of alate production in the three different habitats differed substantially between the annual peas and the two perennial legumes. During the summer, alate production was large and rapid in peas and remained low and constant in clover and alfalfa
- 4 Parasitism was highest in peas. The species composition of parasitoids differed between crops.
- 5 Aphids in annual peas had a higher intrinsic rate of increase and a faster rate of decline than in the two perennial legumes. This explains the presence of both migratory and sedentary forms among pea aphids.
30.
Effect of season and photoperiod on the follicle-stimulating hormone receptors in a subtropical bird
Annual changes in and photoperiodic influence oh the weight of gonads, a parameter of gonadal activity, are much smaller in
female birds than in males. Effect of season and photoperiod on the follicle-stimulating hormone receptors in the testis or
ovary was studied using a subtropical weaver finch. The number of follicle-stimulating hormone binding sites per unit testicular
weight showed a peak in the non-breeding phase; while the total number of binding sites per two testes was maximal in the
breeding phase and minimal in the regressive phase. In contrast, seasonal changes in follicle-stimulating hormone binding
sites in the ovary were less marked. Exposure to short-day during the breeding phase induced marked decreases in the numbers
of binding sites per unit testicular weight and per two testes. These numbers markedly increased after transfer to long-day
during the non-breeding phase. However, there was no significant effect of short-day or long-day exposure on follicle-stimulating
hormone binding sites in the ovary. These results suggest that photoperiod is an effective environmental factor in the regulation
of follicle-stimulating hormone receptors in the testis and the effect is manifested by pronounced changes in the testicular
weight during annual breeding cycle. 相似文献