Specificity of Microscopy

Botanical microscopy is also especially valuable in detecting admixtures of inorganic materials not detectable with standard chemical assessment, such as the presence of dirt mixed in with root material. Similarly, microscopy can also detect when two different parts of the same plant are present. For example, the chemical profile of goldenseal (Hydrastis canadensis) root and leaf is very similar, so contamination of the desired root material with leaf can easily escape detection with standard chemical tests (e.g., HPTLC/HPLC) (AHP 2001). Conversely, it is very easy to identify the presence of leaf material contamination microscopically because the structural differences between root and leaf tissues are readily discernable.

In some cases, the ability to detect trace amounts of adulterants via botanical microscopy is considerable. For example, the Chinese herb market has experienced a long-term problem with adulteration of several species of relatively nontoxic plants (e.g., Akebia, Clematis, and

FIGURE 1.14 The microscopic differentiation of plantain (Plantago lanceolata) and Grecian foxglove (Digitalis lanata). Plantain is characterized by its unicellular stalk and multicellular, narrow, conical head (a and b). Grecian foxglove is characterized by the presence of glandular trichomes with a unicellular stalk and bicellular head (c).

FIGURE 1.14 The microscopic differentiation of plantain (Plantago lanceolata) and Grecian foxglove (Digitalis lanata). Plantain is characterized by its unicellular stalk and multicellular, narrow, conical head (a and b). Grecian foxglove is characterized by the presence of glandular trichomes with a unicellular stalk and bicellular head (c).

Stephania) with plants that contain the highly nephrotoxic and carcinogenic compound aristolochic acid (AA) (e.g., Aristolochia fangchi, Aristolochia manshuriensis). With microscopic analysis, adulteration of the aforementioned three species with as little as 0.3% of these AA-containing plants can be detected in minutes by the presence of crystals (Figure 1.15) that are characteristic of AA-containing plants but absent in the others (Länger 2006, personal communication). Similarly, miscellaneous contaminants such as dirt, insect parts, and rodent hairs, while mostly undetectable with standard chemical assessment, are readily detectable microscopically.

Botanical microscopy also finds considerable utility in fields such as forensics, whereby plant fragments found can be traced to various locales, or in historical investigations, such as tracing the origin of the Shroud of Turin

Aristolochia manshuriensis (stem)

lnniPimnmiiniFiir

Aristolochia fangchi (root)

Transverse section, overview Sclereids and cluster crystals

Transverse section, overview Sclereids and cluster crystals

Cluster crystals

Present

Absent Stephania tetrandra (root) Prismatic crystal sand t, WW *J"'

SEM, crystals Transverse section, overview

Akebia trifoliata (stem)

Crystals within fibers

Akebia trifoliata (stem)

Crystals within fibers

SEM, crystals Transverse section, overview

Transverse section, overview Crystals in fibers

Clematis chinensis (root, rhizome) Crystals absent

Transverse section, overview Crystals in fibers

Clematis chinensis (root, rhizome) Crystals absent

Xylem (rhi

Clematis armandii (stem)

Xylem (rhi

Clematis armandii (stem)

Crystals absent

Crystals absent

Fiber cap

Medullary ray

FIGURE 1.15 Macroscopic and microscopic differentiation of Aristolochia spp. plants containing aristolochic acid (AA) and AA-free plants they may adulterate. Aristolochic acid can cause kidney failure and stomach cancer. (Images courtesy of Prof. Dr. Reinhard Länger, AGES Pharm Med, Vienna, Austria.)

Fiber cap

Medullary ray

FIGURE 1.15 Macroscopic and microscopic differentiation of Aristolochia spp. plants containing aristolochic acid (AA) and AA-free plants they may adulterate. Aristolochic acid can cause kidney failure and stomach cancer. (Images courtesy of Prof. Dr. Reinhard Länger, AGES Pharm Med, Vienna, Austria.)

by the presence of plant fragments and pollens. With the introduction of electron and near-infrared (NIR) microscopy to the discipline, botanical microscopy is continuing its own evolution as a technique. With electron microscopy, even greater levels of magnification, specificity, and detection can be obtained, and with NIR microscopy, even the organic contents of cells can be readily identified.

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