Circulating soluble CD4 directly prevents host resistance and delayed-type hypersensitivity response to Cryptococcus neoformans in mice

In the present study, we examined the effect of soluble CD4 (sCD4) on host resistance and delayed-type hypersensitivity (DTH) response to Cryptococcus neoformans using a novel mutant mouse that exhibits a defect in the expression of membrane-bound CD4 but secretes high levels of sCD4 in the serum. In these mice, host resistance to this pathogen was impaired as indicated by an increased number of live pathogens in the lung. To elucidate the mechanism of immunodeficiency, three different sets of experiments were conducted. First, administration of anti-CD4 mAb restored the attenuated host defense. Second, in CD4 gene-disrupted (CD4KO) mice, host resistance was not attenuated compared to control mice. Third, implantation of sCD4 gene-transfected myeloma cells rendered the CD4KO mice susceptible to this infection, while similar treatment with mock-transfected cells did not show such an effect. These results indicated that immunodeficiency in the mutant mice was attributed to the circulating sCD4 rather than to the lack of CD4+ T cells. In addition, DTH response to C. neoformans evaluated by footpad swelling was reduced in the mutant mice compared to that in the control, and the reduced response was restored by the administration of anti-CD4 mAb. Finally, serum levels of IFN-gamma, IL-12 and IL-18 in the mutant mice were significantly reduced, while there was no difference in Th2 cytokines, such as IL-4 and IL-10. Considered collectively, our results demonstrated that sCD4 could directly prevent host resistance and DTH response to C. neoformans through interference with the production of Th1-type cytokines.     

The ecology and evolution of pollen odors

The literature is reviewed and new evidence presented that pollen produces odors, which serve multiple functions in pollination and defense. Pollen odor, which originates from pollenkitt, comprises volatiles that belong to the same chemical classes found in flower scents, that are in species-specific mixtures, and that contrast with odors of other floral parts. Pollen can also take up volatiles from surrounding floral odors, but this adsorption is selective and varies among species. Pollen odors are more pronounced in insect- than bird- or wind-pollinated plants, suggesting that volatile emission evolved in part under selection to attract pollinators. Pollen-feeding insects can perceive pollen odor and use it to discriminate between different pollen types and host plants. Pollen odor influences bee foraging, including the location of pollen sources, discrimination of flowers with different amounts of pollen, and hostplant recognition by pollen-specialist species. In the few wind-pollinated plants studied, odors of male flowers or pollen are comparatively high in -methyl alcohols and ketones; these volatiles may serve in pollen defense, with some known to repel insects. Pollen odor often includes chemicals with documented defense activity, which is probably aimed mainly at nonpollinator pollen-feeding insects and pathogens; an involvement in pollen allelopathy is also possible. Pollen volatiles comprise chemically diverse compounds that may play multiple roles, and their emission in pollen odor undoubtedly evolved under the principle, and often conflicting, selective pressures to both protect the male gametophyte and increase its dispersal by animals.     

Some molecular and enzymatic properties of a homogeneous preparation of thiaminase I purified from carp liver

A homogeneous preparation of thiaminase I (thiamine:base 2-methyl-4-aminopyrimidine-5-methenyl transferase, EC 2.5.1.2) was obtained from carp liver, for the first time from a nonbacterial source. Its molecular mass was 55 kDa by gel filtration and by SDS—PAGE regardless the presence of the reducing agent, indicating that the native enzyme consists of a single polypeptide chain. The determined sequence of 20 residues at the N-terminal of carp thiaminase I seemed to be unique. The enzyme was tested for ability to decompose a number of thiamine analogues. Even very extensive modifications of the thiazolium fragment were well tolerated, but around the pyrimidine fragment the active center seemed to exert steric restrictions against 1 (N)- and 2 (C)- atoms, while the 4-amino group and untouched 6-carbon atom were absolutely essential for the enzyme action. Numerous nucleophiles could be used by the enzyme as cosubstrates, aniline, pyridine, and 2-mercaptoethanol being the best among compounds tested. Protein chemical modification experiments indicated that histidine residues, carboxyl groups, and sulfhydryl groups may play specific roles in the thiaminase I-catalyzed reaction. Like in the bacterial enzyme, a sulfhydryl group may be a catalytically critical active-site nucleophile. The histidine residues and carboxyl groups may be essential for thiamine binding to the active site.     

Antipredatory Activity of the Weevil Oxyops vitiosa: A Biological Control Agent of Melaleuca quinquenervia

The larvae of the leaf-feeding weevil Oxyops vitiosa, a biological control agent of Melaleuca quinquenervia, are covered with a viscous orange coating that is thought to protect against generalist predators. This coating is gradually lost as the larvae drop to the ground and pupate in subterranean pupal cells. To test the antipredator activity of this species, four immature life stages (early instars, late instars, prepupae, pupae) were exposed to a common generalist predator, the red imported fire ant Solenopsis invicta. Choice tests were conducted by placing an O. vitiosa individual and a control larva of the weevil Neochetina eichhorniae into an arena containing a S. invicta colony and observing subsequent ant behaviors. S. invicta workers contacted O. vitiosa early instars, late instars, and prepupae less frequently than control N. eichhorniae larvae, and upon contact S. invicta was less likely to behave aggressively toward these O. vitiosa life stages than toward N. eichhorniae larvae. However, S. invicta contacted, attacked, and consumed naked (nonencased) O. vitiosa pupae and N. eichhorniae larvae with equal frequency. Encased O. vitiosa pupae buried in sand were not attacked compared to susceptible encased pupae on the sand surface. By shifting from a chemical defense during the larval stages to a physical defense during the pupal stage, O. vitiosa reduces the risk of attack by this generalist predator.     

GRAZING OPTIMIZATION,NUTRIENT CYCLING,AND SPATIAL HETEROGENEITY OF PLANT‐HERBIVORE INTERACTIONS: SHOULD A PALATABLE PLANT EVOLVE?

Abstract.— Can the evolution of plant defense lead to an optimal primary production? In a general theoretical model, Loreau (1995) and de Mazancourt et al. (1998, 1999) have shown that herbivory could increase primary production up to a moderate rate of grazing intensity through recycling of a limiting nutrient, provided several conditions are fulfilled. In the present paper, we assume: (1) grazing intensity is controlled by plants through their level of palatability; and (2) plant fitness is determined by its productivity. We explore the conditions under which such an optimal production may be reached through natural selection. We model two competing plant types that differ only in palatability and are distributed in a patchy landscape determined by the plant‐herbivore interaction. Patch size is determined by herbivore behavior: herbivores recycle nutrient homogeneously within patches, but recycle nutrient proportionally to consumption between patches. The model shows that a strategy of intermediate palatability can be adaptive in response to a small herbivore that lives on and recycles nutrient around one or a few individual plants. For moderately small herbivores, plant palatability may evolve towards one of two local convergent strategies, depending on the initial conditions. For medium‐ to large‐sized herbivores, the nonpalatable strategy is always selected. We discuss the functional and evolutionary implications of these results, and suggest that the traditional dichotomy describing antagonistic and mutualistic interactions may be misleading.     

Deterred oviposition response of Monochamus alternatus (Coleoptera: Cerambycidae) to oviposition scars occupied by eggs

1 The oviposition behaviour and response of Monochamus alternatus females to oviposition scars were investigated in the laboratory. 2 Prior to oviposition, females gnawed at the bark surface of Pinus densiflora bolts to make a wound. Then females turned their bodies 180° to position their ovipositors over the wounds and inserted them under the bark through the wounds. After an oviposition, a jelly was deposited while the ovipositor was still inserted. The females then withdrew their ovipositors and rubbed the oviposition scars with the tips of their abdomens. 3 When searching females encountered oviposition scars, they stopped walking and drummed the surface and inside of the oviposition scars with their maxillary and labial palpi. 4 Eighty-six percent of females left oviposition scars containing single eggs after the palpation. By contrast, when females encountered oviposition scars containing no eggs, 76% of them began to gnaw at the scars and 64% deposited single eggs. The response to artificial oviposition scars was similar to that to vacant oviposition scars made by the females. 5 The results of various observations and experiments showed that the females could recognize oviposition scars and discriminate the scars occupied by single eggs from vacant ones, and suggested that the palpation of oviposition scars was the critical discrimination behaviour, indicating mediation by chemical cues.     

麻竹材化学成分的变异

麻竹(ＤｅｎｄｒｏｃａｌａｍｕｓｌａｔｉｆｌｏｒｕｓＭｕｎｒｏ)是我国南方著名笋竹两用竹种,竹秆粗大通直,大量用于制浆造纸,是我国纸浆材培育的主要竹种之一。化学成分是研究竹材材性的基础和竹材利用的依据。有关麻竹材化学成分的研究未见报道。本文应用正交试验方?..     

水青树和昆栏树茎皮的化学成分

用化学和波谱分析方法从水青树（Ｔｅｔｒａｃｅｎｔｒｏｎ ｓｉｎｅｎｓｅ Ｏｌｉｖ．）茎皮中分离鉴定了５个化合物,分别为丁香甙（ｓｙｒｉｎｇａｎｉｄｅ）、儿茶素（ｃａｔｅｃｈｉｎ）、β－谷甾醇（β－ｓｉｔｏｓｔｅｒｏｌ）、胡萝卜甙（ｄａｕｃｏｓｔｅｒｏｌ）和白桦脂醇（ｂｅｔｕｌｉｎ）,均为从该种植物中首次分得。从昆栏树（Ｔｒｏｃｈｏｄｅｎｄｒｏｎ ａｒａｌｉｏｉｄｅ Ｓｉｅｂ．ｅｔＺｕｃｃ．）茎皮中     

南酸枣果实的成分分析

本文对南酸枣（Ｃｈｏｅｒｏｓｐｏｎｄｉａｓ ａｘｉｌｌａｒｉｓ）鲜果的常规营养尬发和化学成分进行了测定。结果表明,南酸枣果实含有丰富的营养素,果皮内保１８种氨基酸总量达２６．２３～３８．５４ｍｇ／１００ｇ,蛋白质为０．９２％～１．４８％,有机酸含量高达５．２２％～８．１３％,色谱分析显示含有２１种有机酸,其中以柠檬酸、酒石酸、苹果酸和葡萄糖酸等为主要成分,鲜果可食部分还含有丰富的Ｃａ、Ｆｅ、Ｚｎ、     

干旱对上部烟叶细胞结构和化学成分的影响

研究了烟草在土壤含水量为１２％、１６％、２０％的条件下叶片栅栏组织细胞的结构和烟昔日 化学成分的变化规律。结果表明：干旱处理的烟草,叶片栅栏组织细胞内淀粉粒变小,数量变少。叶片中还原性糖、可溶性总糖和Ｋ２Ｏ含量增加,淀粉和烟碱含量减少。干旱程度越深,其变化趋势越明显。