Schwab Suzanne M, Menge John A, Tinker P B
Department of Biology, Eastern Washington University, Cheney.
Department of Plant Pathology, University of California, Riverside.
New Phytol. 1991 Mar;117(3):387-398. doi: 10.1111/j.1469-8137.1991.tb00002.x.
Although the overwhelming majority of non-aquatic vascular plants form vesicular-arbuscular (VA) mycorrhizal associations, the extent of colonization of the host root by any given fungal symbiont varies considerably depending on host and environmental factors. Because VA mycorrhizal fungi are obligate biotrophs, transfer of photosynthate from host to fungus may be an important factor in regulating the extent of VA mycorrhizal formation. Host metabolites must cross the plasma membrane before becoming available to the fungus. Several studies on rates of root exudation under various environmental conditions show a strong correlation between rates of root exudation and percent of root length colonized by VA mycorrhizal fungi. However, passive leakage of simple metabolites from roots as the sole means of regulating fungal colonization seems improbable for an obligate biotroph which has not yet been successfully cultured on any artificial medium. So far there has been insufficient investigation of hormone interactions between symbionts, and of the interference by the fungus in host cell wall synthesis, to evaluate the possible role of these factors in controlling growth of VA mycorrhizal fungi. Cytochemical studies of the host-fungus interface suggest modification of host plasma membrane ATPase activity as arbuscules develop, but the function of this altered activity remains unresolved. The presence of a linked P -photosynthate exchange mechanism on the host plasma membrane analogous to the P -photosynthate translocator known to exist in the outer membrane of chloroplasts remains an uninvestigated possible mechanism for balancing photosynthate demand by the fungus with enhanced P uptake.
尽管绝大多数非水生维管植物会形成泡囊-丛枝（VA）菌根共生体，但任何特定真菌共生体在宿主根中的定殖程度会因宿主和环境因素而有很大差异。由于VA菌根真菌是专性生物营养体，光合产物从宿主向真菌的转移可能是调节VA菌根形成程度的一个重要因素。宿主代谢产物在可供真菌利用之前必须穿过质膜。多项关于不同环境条件下根系分泌物速率的研究表明，根系分泌物速率与VA菌根真菌定殖的根长百分比之间存在很强的相关性。然而，对于一种尚未在任何人工培养基上成功培养的专性生物营养体来说，仅靠根系简单代谢产物的被动渗漏作为调节真菌定殖的唯一方式似乎不太可能。到目前为止，对于共生体之间激素相互作用以及真菌对宿主细胞壁合成的干扰，尚未进行充分研究，因此无法评估这些因素在控制VA菌根真菌生长方面可能发挥的作用。宿主-真菌界面的细胞化学研究表明，随着丛枝的发育，宿主质膜ATP酶活性会发生改变，但这种改变的活性的功能仍未得到解决。宿主质膜上存在一种与叶绿体外膜中已知的磷-光合产物转运体类似的磷-光合产物交换机制，这仍是一种尚未研究的可能机制，用于平衡真菌对光合产物的需求与增强的磷吸收。
