In Restoring the Balance, Think Green!
The Changing Role of Zoos in Plant Conservation
Research Associate, CREW
Cincinnati Zoo and Botanical Garden
Plant conservation is vital for a balanced ecosystem. Habitat conservation is the main focus; however, many endangered species require extreme measures for survival. The Cincinnati Zoo is developing techniques to propagate and preserve these species.
Prologue: A Brief History of CREW
Founded in 1981, the Cincinnati Zoo and Botanical Garden’s Center for Reproduction of Endangered Wildlife (CREW) was established with the goal of applying modern reproductive technologies to the conservation and reproduction of endangered animals. Over the next several years, the research scope expanded, and in 1986 the Plant Conservation Division was established with Dr. Valerie Pence as the director. Now known as the Center for Research of Endangered Wildlife, CREW’s mission is to use science and technology to understand, preserve, and propagate endangered flora and fauna and facilitate the conservation of global biodiversity.
Research at CREW includes assisted reproduction in mammals, amphibians, and birds; genome resource banking of rare plants and animals; basic research conducted to better understand the physiological requirements for the preservation of endangered species; and in vitro propagation of endangered plants.
Plants are an integral part of a functional, balanced ecosystem. At the very least, plants make up the landscape that is home to the fauna of the world. They provide food, shelter, and even entertainment for countless animals, including humans. Plants fuel our economy; feed, shelter, and heal our masses; and clean and recycle our atmosphere, soils, and waters. In their own right, plants are amazing organisms that have evolved in countless ways to survive and prosper in a world from which they cannot run. Second only to insects in species richness, plants are an incredibly diverse group that includes minute mosses, lush ferns, gigantic redwoods, and delicate orchids. Unfortunately, this irreplaceable diversity is disappearing at a feverish rate.
According to the World Conservation Union, the IUCN, nearly 34,000 of the world’s 270,000 vascular plants are threatened with extinction. As with endangered and threatened animals, habitat loss poses the greatest threat to plant diversity. Other major factors that threaten plants include competition from invasive, non-native species and habitat degradation from pollutants. Primary efforts are being made to conserve remaining habitats before it is too late. Unfortunately, many habitats have been severely damaged and preservation of these simply may not be enough. Some species are either on the brink of extinction or will be if current declines in populations continue. These extreme conditions call for extreme measures.
The Cincinnati Zoo and Botanical Garden’s Center for Research of Endangered Wildlife (CREW) has established a program that utilizes modern plant propagation techniques to collect, grow, and preserve highly endangered plant species. Techniques being developed and implemented include plant tissue culture, in vitro collection (IVC), and cryopreservation. The purpose of this presentation is to explain these techniques and to illustrate how they are being used to grow and preserve some of the most threatened plant species known.
Plant Tissue Culture: A Tool for Conservation
Also known as in vitro propagation or micropropagation, plant tissue culture (PTC) is a process through which plant tissue can be grown and indefinitely maintained using an artificial medium conducive to tissue development. This technique is possible because plants have the ability to vegetatively regenerate from somatic, non-sex cells. This is known as totipotency. Plant cells can regenerate new shoots, roots, or even entire plants and it is theoretically possible to produce an infinite number of individuals from an initial cell line.
Most research in PTC has been conducted on economically important crop species. Today, these techniques are commonly applied in the agricultural and horticultural industries. Many ornamental and food crops have their starts not in seed beds in a greenhouse or field, but rather in a tissue culture lab designed for mass production of plantlets using PTC. A few examples include Boston ferns, poinsettias, and even grapes.
Many tissues can be used to start cultures, including seeds, embryos, shoot tips, and leaf tissue. Most of the endangered species being studied at CREW are acquired mostly in the form of seeds, sometimes cuttings, and rarely as entire plants. In all cases, the material is quite limited and seeds may be inviable.
When available material is severely limited, protocols will be developed using closely related species, then these will be applied to the endangered plant.
Application of PTC to endangered species is a rather recent development. Only a handful of institutions throughout the world are actively applying tissue culture research to plant conservation. Unlike research with crop species for which material is readily available, endangered species are difficult to obtain and material such as seeds can be in scarce supply. An alternative method for acquiring different lines is in vitro collection, a technique that is currently being developed at CREW.
In Vitro Collection: Collecting Plants One Small Piece at a Time
In vitro collection is a technique in which researchers, instead of collecting entire plants or their seeds, take small cuttings of leaves or buds, place them on media for growth initiation and transport, and take them to the lab where they can be grown into new plants. Using this method, rare species can be collected with minimal, if any, negative impact on the habitat or the plants themselves. Using IVC, a species can be extensively sampled from wild populations without removing a single plant. In this way, the genetic diversity of a species can be better represented in the collections.
The technique of IVC was developed over several years of research in both tropical and temperate ecosystems. Today, the technique can be successfully applied to a wide variety of plant species. It has been used to collect eleven endangered plant species from the United States. These include annuals, perennial herbs, and even woody shrubs.
Cryopreservation: Freezing for the Future
After propagation protocols have been developed for an endangered species, each genetic line is placed in liquid nitrogen-long-term storage. This is known as cryopreservation. At 196ºC, the temperature of liquid nitrogen, all cellular activity ceases and living tissue, in effect, is suspended in time. A variety of tissue can be frozen from seeds to shoot tips. With the PTC lines of endangered species, shoot tips are most commonly used. Regardless of the tissue being preserved, the trick is to treat the tissue in such a way as to reduce cell damage.
Upon freezing, water in tissue cells expands and breaks cell membranes. To prevent this, various cryoprotectants and procedures are used to treat the tissue before freezing. The general goal is to replace the water in the cells with other substances that do not expand upon freezing. This preserves the cell membranes and allows the tissue to survive. When these techniques are developed for a particular species, cryopreserved tissues are placed in liquid nitrogen dewars for long-term storage.
At CREW, many species are currently preserved using this technique. These will be maintained indefinitely and may be revived in the future if needed. Preserved species may one day be used for reintroductions into reclaimed habitats or for additional study of the species.
The Endangered Species Propagation Program: Applying the Tools to the Species
The Endangered Species Propagation Program (ESPP) is focused on applying the techniques just described to many critically endangered species. Those species selected for research all face specific hurdles to successful propagation that cannot be overcome using traditional means such as seed germination and cuttings. These species face eminent extinction if measures are not taken to propagate the species. In 1995, and again in 1997, the Institute of Museum and Library Services awarded a grant for research within this program that targets endangered U.S. species.
This project, a collaborative effort between CREW and the Center for Plant Conservation (CPC), is focused on nearly 30 endangered plants from throughout the United States. These species are part of the CPC’s National Collection and were chosen based on the above-mentioned criteria. Plants being studied represent a variety of species from throughout the United States. These include species from wetlands, mountains, deserts, grasslands, forests, and the Florida scrub. To date, propagation and cryopreservation protocols have been developed for many of these species. For others, the research continues.
Conservation of the world’s plants is imperative. By preserving remaining habitats and reclaiming and restoring others, our world will continue to survive and prosper. However, those species on the brink of extinction require extreme and often creative measures to ensure their survival. Research at CREW is focused on these species for which little time remains. Individual requirements and limitations must be addressed for each species, and the protocols for effective propagation must be tailored to each. By developing such protocols, endangered species that have been impossible to propagate ex situ can now be produced and maintained for study. Additionally, the long-term survival of these important species can be ensured by cryopreserving the genetic lines. These efforts are not foolproof, and success is not guaranteed. However, if efforts are not made, the future for these species is, at best, uncertain.
The Center For Plant Conservation (CPC) is gratefully acknowledged for their collaboration in this project. CPC-affiliated gardens are also gratefully acknowledged for selecting species and supplying plant material, information, and help with fieldwork. Special thanks to The Nature Conservancy, U.S. Fish and Wildlife, and the North Carolina Plant Conservation Program. This research was supported, in part, by grants from the Institute of Museum and Library Services, No. IC-50056-95, No. IC-70248-97, and No. Ic-00034-00.