Downes G M, Alexander I J, Cairney J W G
Department of Plant and Soil Science, University of Aberdeen, Meston Building, Aberdeen AB9 2UE, UK.
New Phytol. 1992 Sep;122(1):141-152. doi: 10.1111/j.1469-8137.1992.tb00060.x.
An age sequence of mycorrhizas formed by Paxillus involutus (Batsch. ex Fr.) Fr. and Tylospora fibrillosa (Burt.) Donk was sampled from 6-9-month-old seedlings of Picea sitchensis (Bong.) Carr. grown on peat in root observation chambers. Information about the ageing process was obtained from co-ordinated studies of mycorrhizal morphology, anatomy, ultrastructure and cell vitality (indicated by FDA-staining). Newly produced mycorrhizas were pale and turgid over most of their length with obvious extramatrical mycelium. Most mycorrhizas over 50 d old had a light turgid apical portion and a darkened wrinkled proximal portion: extramatrical mycelium was less obvious. Many remained in this state until the sampling stopped at day 142, but some were completely darkened before day 50. The morphological appearance of a mycorrhiza was not a good indicator of its chronological age. Most mycorrhizas displayed periodic busts of growth which added portions of young turgid cortex to an ageing axis. The percentage of cortical cells showing nuclei in 1 μm sections of the apical 1 mm declined from 40-50 % in mycorrhizas < 25 d old to 5-15 % in mycorrhizas 110-140 d old. Cortical cells became more vacuolate as they aged and the number of organelles appeared to decline. Senescence proceeded from the outer to the inner cortex and from proximal to distal regions. Degenerate cortical cells were present in the Hartig net zone of mycorrhizas over 25 days old. Cortical cell degeneration preceded, but was closely followed by, degeneration of adjacent Hartig net. The FDA study supported the general pattern and timing of cell death interpreted from the morphological and ultrastructural study. Cortical/Hartig net fluorescence declined markedly in mycorrhizas over 70-85 d old. The stele was the last tissue in the mycorrhiza to degenerate. It is suggested that a mycorrhiza ceases to function in nutrient and water uptake when no living cortical/Hartig net interface remains. In this study a few mycorrhizas became non-functional by day 31. For most mycorrhizas the major decline in function took place after 85 days. This estimate is in broad agreement with the estimates of mycorrhizal life span obtained from biomass studies in the field.
从生长在根观察室泥炭土上的6 - 9月龄西加云杉（Picea sitchensis (Bong.) Carr.）幼苗中采集了由卷缘桩菇（Paxillus involutus (Batsch. ex Fr.) Fr.）和纤维状丝膜菌（Tylospora fibrillosa (Burt.) Donk）形成的菌根的年龄序列。通过对菌根形态、解剖结构、超微结构和细胞活力（用FDA染色表示）的协同研究获得了有关衰老过程的信息。新形成的菌根在其大部分长度上颜色浅且饱满，有明显的根外菌丝体。大多数超过50天龄的菌根有一个浅色饱满的顶端部分和一个变黑起皱的近端部分：根外菌丝体不太明显。许多菌根一直保持这种状态直到第142天采样结束，但有些在50天前就完全变黑了。菌根的形态外观并不是其实际年龄的良好指标。大多数菌根显示出周期性的生长高峰，在衰老的轴上增加了年轻饱满的皮层部分。在顶端1毫米的1微米切片中，显示有细胞核的皮层细胞百分比从小于25天龄的菌根中的40 - 50%下降到110 - 140天龄的菌根中的5 - 15%。随着皮层细胞衰老，它们变得更加液泡化，细胞器数量似乎减少。衰老从外层皮层向内层皮层以及从近端区域向远端区域进行。超过25天龄的菌根的哈氏网区域存在退化的皮层细胞。皮层细胞退化先于相邻哈氏网的退化，但二者紧密相随。FDA研究支持了从形态学和超微结构研究中解释的细胞死亡的总体模式和时间。超过70 - 85天龄的菌根中皮层/哈氏网荧光明显下降。中柱是菌根中最后退化的组织。有人认为，当不再存在活的皮层/哈氏网界面时，菌根就停止了在养分和水分吸收方面的功能。在本研究中，一些菌根在第31天就失去了功能。对于大多数菌根来说，功能的主要下降发生在85天之后。这一估计与从田间生物量研究中获得的菌根寿命估计大致一致。
