菌根真菌促进植物吸收利用氮素机制的研究进展

作为自然界最为普遍的一种植物共生体,菌根能够极大地促进植物对氮素的吸收和利用,其中菌根真菌在共生结构功能中发挥了重要作用。本文分别从菌根解剖构造、生理生化和分子生物学方面系统总结了菌根真菌促进植物吸收和利用氮素的研究现状。重点介绍了菌根真菌可利用的氮素形态及影响其利用的主要因素、菌根真菌的氮代谢途径GS-GOGAT以及菌根真菌中存在的鸟氨酸循环途径,指出精氨酸是菌丝内氮转运的主要形式,NH3可能为菌根真菌和植物界面质外体的主要转运形式。     

Building a mycorrhizal cell: How to reach compatibility between plants and arbuscular mycorrhizal fungi

Abstract

Arbuscular mycorrhizal fungi occur throughout the majority of ecosystems supporting host plant nutrition. Recent findings describe the accommodation of the fungus by the root cell as a crucial step for compatibility between the partners. We discuss here the novel aspects of cellular plant-fungus interactions, with a particular attention to the interface compartment, the unique apoplastic space hosting intracellular fungal structures. The main features of arbuscular mycorrhizal colonization are examined and recent information in the field of plant and fungal cell responses during the establishment of the symbiosis is discussed. Differences between the colonization of root epidermal and cortical tissues are discussed, highlighting the growing interest in the role of epidermal cells during the first and decisive steps of the symbiosis. New approaches such as root organ cultures, in vivo observations, GFP tagging and mutant plant analysis are commented on and information from these is compared with that gained from more traditional methods. In particular, the use of plant mutants is depicted as a powerful tool for dissecting and understanding the genetic and cellular aspects of plant/fungus compatibility. Finally, perspectives in this field are outlined through the application of these approaches to the currently unanswered questions.     

Parasitic castration of plants by fungi

If the production of genetically variable offspring is a mechanism of host defense against parasites, then parasites capable of suppressing sexual reproduction in hosts may gain a selective advantage over parasites that do not do so. Recent work has shown that a range of systemic fungi infecting plants sterilize their hosts, effectively preventing coevolutionary responses by host populations to avoid infection, while stimulating clonal spread of the infected plant. Indeed, parasitic castration of plants may represent a widespread fungal adaptation.     

Thigmo responses in plants and fungi

Thigmo mechanisms are adaptations that permit a plant to alter growth rates, change morphology, produce tropisms, avoid barriers, control germination, cling to supporting structures, infect a host plant, facilitate pollination, expedite the movement of pollen, spores, or seeds, and capture prey. Through these varied functions, plant thigmo systems have evolved impressive controls of cell differentiation, localized growth rates, regulated synthesis of novel products, and some elegant traps and projectile systems. For most thigmo events, there will be a dependence upon transmission of a signal from the cell wall through the plasmalemma and into the cytoplasm. We propose the possible involvement of integrin-like proteins, Hechtian strands, and cytoskeletal structures as possible transduction components. Many thigmo mechanisms may use some modification of the calcium/calmodulin signal transduction system, though the details of transduction systems are still poorly understood. While transmission of thigmo signals to remote parts of a plant is associated with the development of action potentials, hormones may also play a role. Thigmo mechanisms have facilitated an enormous array of plant and fungal adaptations that make major contributions to their success despite their relatively sessile or immobile states.     

Occurrence of fusicoccanes in plants and fungi

The literature on substances structurally related to fusicoccin shows that its molecular design is not unique. Compounds of this type with a dicyclopenta[a,d]cyclooctane skeleton (the 585 ring system) are often encountered in nature. The compounds, systematically reviewed, comprise a single class of fusicoccane-type terpenoids characterized by the presence of the dicyclopenta[a,d]cyclooctane system in the structure of these molecules. The review is arranged according to the taxonomy of the organisms producing these terpenoids; it is shown that compounds of this type, including physiologically active ones, are found in the major systematic divisions: fungi, lower and higher plants, and animals (insects). Chemical, analytical, and biogenetic data are given for each compound, as well as data on their physiological activity and the mechanism of their action on plants. Nomenclature is proposed for the fusicoccane-type compounds.     

Sensing of UV-B radiation by plants

Daylight UV-B (UV-B) radiation (280–315 nm) is, because of its photochemical effects and potential destructive impact, an important environmental factor for plants. After decades of fruitless attempts, a receptor molecule, UVR8, for sensing of ambient UV-B radiation by plants has been characterized, and the initial steps in signal transduction have been identified. There are, however, other signaling pathways, and there are apparent contradictions in the literature. There is still much to find out about the complex signaling network in plants for processing of information about the daylight surrounding them.     

Positive effects of cyanogenic glycosides in food plants on larval development of the common blue butterfly

Cyanogenesis is a widespread chemical defence mechanism in plants against herbivory. However, some specialised herbivores overcome this protection by different behavioural or metabolic mechanisms. In the present study, we investigated the effect of presence or absence of cyanogenic glycosides in birdsfoot trefoil (Lotus corniculatus, Fabaceae) on oviposition behaviour, larval preference, larval development, adult weight and nectar preference of the common blue butterfly (Polyommatus icarus, Lycaenidae). For oviposition behaviour there was a female-specific reaction to cyanogenic glycoside content; i.e. some females preferred to oviposit on cyanogenic over acyanogenic plants, while other females behaved in the opposite way. Freshly hatched larvae did not discriminate between the two plant morphs. Since the two plant morphs differed not only in their content of cyanogenic glycoside, but also in N and water content, we expected these differences to affect larval growth. Contrary to our expectations, larvae feeding on cyanogenic plants showed a faster development and stronger weight gain than larvae feeding on acyanogenic plants. Furthermore, female genotype affected development time, larval and pupal weight of the common blue butterfly. However, most effects detected in the larval phase disappeared for adult weight, indicating compensatory feeding of larvae. Adult butterflies reared on the two cyanogenic glycoside plant morphs did not differ in their nectar preference. But a gender-specific effect was found, where females preferred amino acid-rich nectar while males did not discriminate between the two nectar mimics. The presented results indicate that larvae of the common blue butterfly can metabolise the surplus of N in cyanogenic plants for growth. Additionally, the female-specific behaviour to oviposit preferably on cyanogenic or acyanogenic plant morphs and the female-genotype-specific responses in life history traits indicate the genetic flexibility of this butterfly species and its potential for local adaptation.     

Control of cellulose hydrolysis by fungi

Summary The extent of filter paper degradation by extracellular preparations fromT. reesei and its mutants with a decreasing level of -glucosidase and an increasing level of endoglucanase has been determined. The ability to degrade cellulose is restricted by the level of endoglucanase and not by -glucosidase.     

Rhizosphere communication of plants, parasitic plants and AM fungi

Plants use an array of secondary metabolites to defend themselves against harmful organisms and to attract others that are beneficial. However, the attraction of beneficial organisms could also lead to abuse by malevolent organisms. An exciting example of such abuse is the relationship between plants, beneficial mutualistic arbuscular mycorrhizal fungi and harmful parasitic plants. Signalling molecules called strigolactones, which are secreted by plant roots in low concentrations, induce the growth of both obligate biotrophs. Here, we review the importance of strigolactones for these two interactions and discuss possible developments that should further clarify the role of these signalling molecules in rhizosphere processes.     

Circular proteins from plants and fungi

Circular proteins, defined as head-to-tail cyclized polypeptides originating from ribosomal synthesis, represent a novel class of natural products attracting increasing interest. From a scientific point of view, these compounds raise questions of where and why they occur in nature and how they are formed. From a rational point of view, these proteins and their structural concept may be exploited for crop protection and novel pharmaceuticals. Here, we review the current knowledge of three protein families: cyclotides and circular sunflower trypsin inhibitors from the kingdom of plants and the Amanita toxins from fungi. A particular emphasis is placed on their biological origin, structure, and activity. In addition, the opportunity for discovery of novel circular proteins and recent insights into their mechanism of action are discussed.     

远紫外辐射诱导紫杉产生的活性氧

为了解活性氧和自由基在介导远紫外辐射对植物伤害上的作用 ,在实验室内用远紫外线源对紫杉 (TaxuscuspidataSieb .etZucc .)苗进行了 4周的辐射处理。每周取样 ,对针叶的有机自由基及离体叶绿体的O-·2 和1O2 分别进行了电子自旋共振 (ESR)检测 ,以了解它们各自的相对重要性。结果表明针叶的有机自由基水平最能说明远紫外辐射剂量的积累效应。其次是叶绿体产生的O-·2 。叶绿体产生的1O2 也随辐照时间的增加而略有增加 ,但由于本底数值过高 ,它在介导远紫外辐射引起的伤害上可能不如O-·2 重要     

Control of growth and differentiation by cyclic AMP in fungi

InSaccharomyces cerivisiae intracellular cAMP mediates environmental signals that regulate cellular metabolism and growth. The studies on the cAMP-requiring mutants and their suppressors in the yeast revealed that cAMP-dependent protein phosphorylation is involved in the G1 phase of the cell cycle, stimulation of the phosphoinositide pathway and the post-meiotic stage of spourlation, and that inhibition of cAMP-dependent protein phosphorylation is required to go into the GO stage of and to induce meiotic division. Growth of some filamentous fungi was observed with significantly reduced levels of cAMP, suggesting that cAMP may not be essential for growth in some species of fungi. Germination of fungal spores, yeast-mycelium dimorphism and hyphal morphogenesis of several species of fungi were affected by cAMP. cAMP was involved in extension of hyphae, formation of hyphal aggregates and fruit body formation. Phosphorylation of cellular proteins is required in these processes, and the nature of these proteins phosphorylated by cAMP-dependent protein kinase is important to the understanding of the role of cAMP for growth and differentistion in fungal cells.     

Model of microtine cycles caused by lethal toxins in non-preferred food plants

A recent model of microtine cycles has hypothesized that plant chemical defences can drive the precipitous decline phase, through periodic lethal toxin production (PLTP) by non-preferred plant foods. Here we enumerate possible mechanisms using a previously published model of optimal foraging by one consumer (microtine rodent) of two types of food plant (1 preferred and 1 non-preferred). Rate constants for each of the model parameters were sought from the extensive literature on vole cycles. For a range of likely values of input parameters, we evaluated model fit by applying five empirically derived criteria for cyclic behaviour. These were: cycles with a period length of 2-5 yr, peak densities of 100-350 voles per ha and trough densities of 0-25 ha(-1), ratio of peak to trough densities of 10-100, and the occurrence of a catastrophic collapse in the vole population followed by a prolonged low phase. In contrast to previous models of food-induced microtine cycles, the optimal foraging model successfully reproduced the first four criteria and the prolonged low phase. The criterion of population collapse was met if the non-preferred food began producing lethal toxins at a threshold grazing intensity, as predicted by PLTP. Fewer criteria could be met in variations on the model, in which the non-preferred food was equally as nutritious as the preferred food or was continuously toxic.