Department of Biology and The Biotron, The University of Western Ontario, London, ON, Canada N6A 5B7.
Phytochemistry. 2012 Jun;78:44-53. doi: 10.1016/j.phytochem.2012.02.024. Epub 2012 Apr 19.
American ginseng (Panax quinquefolius L.) produces triterpenoid saponins, ginsenosides, that possess mild fungitoxic activity toward some common ginseng leaf pathogens. However, numerous oomycete root pathogens of ginseng, most notably Pythium irregulare Buisman, are able to partially deglycosylate 20 (S)-protopanaxadiol ginsenosides Rb1, Rd and gypenoside XVII via extracellular glycosidases, leading to a common product, ginsenoside F2. Conversion of the common 20 (S)-protopanaxadiols into F2 requires both β (1→6) and β (1→2) glucosidase activity. In the present study, the ability of nine distinct isolates of P. irregulare, as well as a P. ultimum Trow isolate and two isolates of Trichoderma hamatum (Bonord.) Bainier, to deglycosylate 20 (S)-protopanaxadiols, in vitro was examined. The pathogenicity of each isolate was also examined by scoring the severity of disease symptoms caused by each in separate inoculations of one- and two-year old ginseng seedlings. Disease severity was scored using a disease severity index, as well as by taking F(v)/F(m) measurements of leaves during a 14-day infection period. Based on these measurements, it was concluded that (1) the use of direct F(v)/F(m) measurements correlates strongly with observations of disease severity (R(2)=0.79), and that (2) the pathogenicity of P. irregulare isolates correlates with their ability to deglycosylate ginsenosides (R(2)=0.57). These results further support the hypothesis that the pathogenicity of P. irregulare on ginseng roots is dependent, in part, on the ability of this organism to deglycosylate ginsenosides.
西洋参（ Panax quinquefolius L. ）产生三萜皂苷，人参皂苷，具有对一些常见的人参叶病原菌的温和抑菌活性。然而，人参的许多卵菌根病原菌，特别是不规则节杆菌（ Pythium irregulare Buisman ），能够通过细胞外糖苷酶部分去糖基化 20 （ S ） -原人参二醇人参皂苷 Rb1 、 Rd 和绞股蓝皂苷 XVII ，导致常见产物人参皂苷 F2 。将常见的 20 （ S ） -原人参二醇转化为 F2 需要β（ 1→6 ）和β（ 1→2 ）葡萄糖苷酶活性。在本研究中，研究了 9 种不同的不规则节杆菌分离株以及一种 P. ultimum Trow 分离株和两种哈茨木霉（ Trichoderma hamatum （ Bonord. ） Bainier ）分离株体外水解 20 （ S ） -原人参二醇的能力。还通过对 1 年和 2 年生人参幼苗的单独接种中每种分离株引起的疾病症状的严重程度来检查每个分离株的致病性。通过使用疾病严重程度指数以及在 14 天感染期间对叶片进行 F(v)/F(m)测量来对疾病严重程度进行评分。基于这些测量，得出以下结论：（ 1 ）直接使用 F(v)/F(m)测量与疾病严重程度的观察结果密切相关（ R 2 = 0.79 ），并且（ 2 ）不规则节杆菌分离株的致病性与其水解人参皂苷的能力相关（ R 2 = 0.57 ）。这些结果进一步支持了这样的假设，即不规则节杆菌对人参根的致病性部分取决于该生物体水解人参皂苷的能力。
