Smith S E, Smith F A
Departments of Agricultural Biochemistry (Waite Agricultural Research Institute), The University of Adelaide, Adelaide, South Australia, Australia, 5001.
Departments of Botany, The University of Adelaide, Adelaide, South Australia, Australia, 5001.
New Phytol. 1990 Jan;114(1):1-38. doi: 10.1111/j.1469-8137.1990.tb00370.x.
In this review we compare the structure and function of the interfaces between symbionts in biotrophic associations. The emphasis is on biotrophic fungal parasites and on mycorrhizas, although necrotrophic parasitic associations and the Rhizobium/legume symbiosis are mentioned briefly. We take as a starting point the observations that in the parasitic associations nutrient transport is polarized towards the parasite, whereas in mutualistic associations it is bidirectional. The structure and function of the interfaces are then compared. An important common feature is that in nearly all cases the heterotrophic symbiont (whether mutualistic or parasitic) is located topologically outside the cytoplasm of the host cells, in an apoplastic compartment. This means that nutrient movements across the interface must involve transport into and out of this apoplastic region through membranes of both organisms. Basic principles of membrane transport in uninfected cells are briefly reviewed to set the scene for a discussion of transport mechanisms which may operate in parasitic and mycorrhizal symbioses. The presence and possible roles of ATPases associated with membranes at the interfaces are discussed. We conclude that cytochemical techniques (used to demonstrate the activity of these enzymes) need to he extended and complemented by biochemical and biophysical studies in order to confirm that the activity is due to transport ATPases. Nevertheless, the distribution of activity appears to he in accord with polarized transport mechanisms in some pathogens and with bidirectional transport in mycorrhizas. The absence of ATPases on many fungal membranes needs re-examination. We emphasize that transport mechanisms between mycorrhizal symbionts cannot be viewed simply as the exchange of carbon for phosphate. Additional features include provision for transport of carbon and nitrogen as amino acids or amides and for ions such as K and H involved in the maintenance of charge balance and pH regulation, processes which also occur in parasitic associations. Interplant transport of nutrients via mycorrhizal hyphae is discussed in the context of these complexities. Some suggestions for the directions of future work are made. CONTENTS Summary 1 I. Introduction 2 II. The availability of nutrients to the symbionts 3 III. Structure of interfaces between symbionts 4 IV. Identity of nutrients transferred: an overview 12 V. Membrane transport: basic principles 14 VI. Transport at the interface of biotrophic symbioses 15 VII. Regulation of pH in biotrophic symbioses 25 VIII. Conclusions: 26.
在本综述中，我们比较了生物营养型共生关系中共生体之间界面的结构和功能。重点是生物营养型真菌寄生物和菌根，尽管也简要提及了坏死营养型寄生关系和根瘤菌/豆科植物共生关系。我们以以下观察结果为出发点：在寄生关系中，营养物质运输朝着寄生物极化，而在互利共生关系中则是双向的。然后比较了界面的结构和功能。一个重要的共同特征是，几乎在所有情况下，异养共生体（无论是互利共生还是寄生）在拓扑学上都位于宿主细胞细胞质之外的质外体区室中。这意味着营养物质跨界面的移动必须涉及通过两种生物体的膜进出这个质外体区域。简要回顾了未感染细胞中膜运输的基本原理，为讨论可能在寄生和菌根共生中起作用的运输机制奠定基础。讨论了与界面处膜相关的ATP酶的存在及其可能的作用。我们得出结论，细胞化学技术（用于证明这些酶的活性）需要通过生化和生物物理研究加以扩展和补充，以确认该活性是由运输ATP酶引起的。然而，活性分布似乎与某些病原体中的极化运输机制以及菌根中的双向运输一致。许多真菌膜上不存在ATP酶这一情况需要重新审视。我们强调，菌根共生体之间的运输机制不能简单地视为碳与磷酸盐的交换。其他特征包括以氨基酸或酰胺形式运输碳和氮以及运输参与维持电荷平衡和pH调节的离子（如K和H），这些过程在寄生关系中也会发生。在这些复杂性的背景下讨论了营养物质通过菌根菌丝在植物间的运输。对未来工作的方向提出了一些建议。目录摘要1 一、引言2 二、共生体可利用的营养物质3 三、共生体之间界面的结构4 四、转移营养物质的种类：概述12 五、膜运输：基本原理14 六、生物营养型共生界面处的运输15 七、生物营养型共生中的pH调节25 八、结论：26
