Collection Storage And Vouchering Of Plants

7.2.1 Collection of Plants in the Field: Do's and Don'ts

When collecting plants in the field for natural product extractions, it is important to be properly prepared. Based on our experience, we suggest that you do the following:

• Wear field clothes (Figure 7.1) and cover yourself head to toe if collecting is to be in the cold of winter or when mosquitos or deer/black flies are in abundance.

FIGURE 7.1 Casey Lu (far right) and colleagues (from Humboldt State University Department of Biological Sciences, at Arcata, CA) on a field trip at a site along the coast of the Pacific Ocean where medicinal plants were being collected. (1997 photo by Peter Kaufman.)

• Take along a note pad and pencil to record information about the collecting site location, soil conditions, ecological habitat, date of collection, plant identity, and who collected the plant(s).

• Take along a pocket-size field-guide (with photos, drawings, and good, usable identification keys) to the local flora and a hand lens to help you identify the plant.

• If you are collecting live plants, take along some Zip-lock™ plastic bags of various sizes in which to put the samples after collecting plants onsite (Figures 7.2 and 7.3). Slips of recycled paper are good to have for notes on plant identity with your collected specimens that match up with your field notes about the respective collections.

• Take soil samples from each site so as to later get information on soil nutrient, soil pH, and soil type where each plant grows.

• When you collect plants for extracts, it is important to get representative samples of all parts available: roots, vegetative shoots, bark from stems (if woody plant), flowers, fruits, and seeds (if mature).

• When collecting plants in the field, do not take every last plant in the population, especially if the plant is rare, threatened, or endangered.

FIGURE 7.2 Casey Lu is shown collecting a medicinal plant in the field north of Areata, CA. (Photo by Peter Kaufman.)

• In the process of collecting herbaceous perennial plants (plants that come from the same mother plant year after year), leave some of the original plant intact where it is growing so that it can reproduce during the current and following years. Many of these plants take years to produce even a small amout of new biomass every year.

• As native Amerinds do, thank the plant for providing you with material for your extracts! I think we all do this in various ways when we collect plants in the home garden for food or for aesthetic purposes, or when we are collecting wild edible plants or mushrooms in the field.

• If you are collecting mushrooms or puffballs in the field, wrap the fruiting bodies in wax paper and place them in a collecting basket or other suitable container where they will not become squashed. This will help for later identification and/or making spore prints from the fruiting bodies. This is impossible with giant puffballs (Calvatia gigantea); these can be collected intact and placed in large paper shopping bags. Some of these mushrooms attain a diameter of 0.5 m.

7.2.2 Storage of Plants at Low Temperatures in a Frozen State

Once one comes in from collecting plants in the field, it is a good idea to freeze them immediately in a freezer at -20°C or a commercial freezer held at -80°C. This is to prevent any degradation of the plant material or any enzymatic changes that alter or degrade naturally occurring metabolites. Natural drying of the plant material can also be done if yield of metabolites is not critical. This

FIGURE 7.3 Casey Lu placing a specimen of medicinal plant in a Zip-Lock™ bag while on a field trip north of Areata, CA. (Photo by Peter Kaufman.)

is usually the case for plants used for dyeing fibers, but for extraction of medicinal compounds from plants, the use of dried plant material is not desirable due to degradation of naturally occurring metabolites during the drying process. Rather, it is best to rely on the use of frozen plant material. The only exception is with seeds. They are usually dried to a low moisture content to prolong seed viability. If the drying process is slow and the temperature is at ambient level, very little degradation of stored metabolites in the seeds occurs.

7.2.3 Vouchering of Plants Collected in the Field 7.2.3.1 Preparation of Dry Specimens

Dried plant specimens are prepared in order to have them available at any time as voucher specimens representing typical plants that were collected in the field and used for plant extracts. They are also called herbarium specimens. To prepare dried plant specimens, they are placed between single newspaper sheets then placed in a sandwich consisting of a dry blotter above and below the newspaper sheets. A piece of corrugated cardboard (with air spaces present) is then placed above and below each blotter. Successive sandwiches are placed atop one another then compressed between two wood-slatted frames and tied together tightly with straps. The entire assembly is then placed upright on its side over a heat source such as a radiator or a plant drier with the heat on a moderate temperature (e.g., 35 to 40°C). The specimens are allowed to dry this way for 48 h or longer. Rapid drying assures that plant pigments are well preserved; if the drying process is slow, chlorophylls will degrade and the leaves will appear yellow; flower pigments also fade badly with slow drying. If plant specimens are very high in water content, it is a good idea to replace the blotters with dry ones several times during the drying process.

Once plant specimens are dry, they can be mounted flat (with glue or cement) on heavy paper of sufficient size to accommodate the specimen and a label with information about the plant, location of collecting site, collector, date of collection, genus and species of the plant, and the family to which the plant belongs. The label may be placed in the lower right-hand corner of the sheet of heavy paper. To avoid damage to the dry, mounted specimen, the entire sheet can be covered with Saran-Wrap™. Dried sheets with plants mounted on them are usually stored in an air-tight cabinet in which one can use natural insect repellents such as dried lavendar (Lavandula officinalis) or neem (Azadirachta indica).

7.2.3.2 Keeping a Good Log Book with Plant Collection Inventory

One should always keep a log book of the plants that have been collected and then frozen. A back-up inventory on the computer is also a good idea. Why is this important? Sometimes labels with collected plant material become lost. Sometimes, one needs to quickly examine lists of collected plants without going through all of the frozen material! And sometimes, one needs to send such lists to others involved in the project.

7.2.3.3 Representative Living Plant Specimens from Field Collections

In our experience, we have found it to be a good idea to collect seeds and/or living specimens of the plants that are to be used for extraction of natural products. We do this in order to have the living plants on hand, e.g., medicinal plants, dye plants, or culinary herbs garden or in a greenhouse. These can then be used for later extractions or experimental treatments to enhance metabolite biosynthesis; this is especially important when access to the original collecting site is not possible or convenient. A good example of this is with tree of joy, Camptotheca accuminata, which is the source of the drug camp-tothecin used to treat patients with prostate cancer. Our original seed came from China. The seed used in our experiments conducted in a greenhouse came from progeny from the original Chinese seed which was grown in Louisiana. These seeds from the tree of joy progeny were kindly provided by Mr. Tracy Moore, President of XyloMed Research Inc. in Monroe, LA (Figure 7.4). The results from these studies are provided in the research essay in Chapter 3, Section 3.2 written by Atul Rustgi, Ashish Goyal, and Kathryn Timberlake.

FIGURE 7.4 (Left to right) Dr. Stanley Carpenter, LSU; Dr. Zhijun Liu, Post-Doctoral Research Fellow at LSU; Tracy Moore, President of XyloMed Research, Inc.; and Dr. John D. Tarven, LSU, while on visit to Beijing, Peoples Republic of China in November, l996 to collect seed from different native populations of tree ofjoy, Camptotheca accumi-nata, the source of the drug, camptothecin, used to treat cancer patients. (Photo courtesy of Tracy Moore.)

FIGURE 7.4 (Left to right) Dr. Stanley Carpenter, LSU; Dr. Zhijun Liu, Post-Doctoral Research Fellow at LSU; Tracy Moore, President of XyloMed Research, Inc.; and Dr. John D. Tarven, LSU, while on visit to Beijing, Peoples Republic of China in November, l996 to collect seed from different native populations of tree ofjoy, Camptotheca accumi-nata, the source of the drug, camptothecin, used to treat cancer patients. (Photo courtesy of Tracy Moore.)

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