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An Introduction to Plant Biodiversity and Bioprospecting

Ramya Krishnan1, *, Sudhir P. Singh2, and Santosh Kumar Upadhyay3 *

1 CSIR-National Institute of Interdisciplinary Science and Technology, Thiruvananthapuram, Kerala, India

2 Center of Innovative and Applied Bioprocessing, (CIAB), Mohali, India

3 Department of Botany, Panjab University, Chandigarh, UT, India

1.1 Introduction

There is an extensive diversity in life that has been disentangled and organized into coherent units called taxa. The five kingdom system of classification has simplified the life forms into five groups. These groups orchestrate information concerning a wide variety of characteristics such as morphological, genetic, metabolomic, ecological, etc. Kingdom Plantae is one of these five kingdoms that consists of all the plant forms on earth and is rich in its metabolomic characteristic. This kingdom is highly diverse and is composed of both seed bearing (Phanerogams) and seedless (Cryptogams) plants forming five broadly classified groups, i.e. algae, bryophytes, pteridophytes, gymnosperms, and angiosperms, which are evolutionarily related. Each of these groups consists of hundreds of thousands of known species, which in turn consist of a variety of chemicals called metabolites or more specifically secondary metabolites. These secondary metabolites or natural products are believed to possess certain biological activities that are used by the producer for their environmental and competitive fitness. Progressively, it became a paradigm that all the plants possess some potent biologically active substance/s that could have great commercial/therapeutic value to humans. It has been often argued that the currently available knowledge regarding the chemical diversity of the plant biome represents only a fraction of that diversity, hence paving way toward further explorations. Thus, their rich metabolomic diversity and its knowledge increase the opportunity for humans to utilize plants as a key resource for bioprospecting.

1.2 What is Bioprospecting

Let us widen our imaginations and visualize an underdeveloped rural village in India, where an old wise man is treating a sick man with his self-made herbal concoction comprising the roots of some wild plants, or, let us visualize him trying to squeeze a stream of juice from a bunch of leaves upon a snake-bitten area of a person's leg. Just after a few days, the concoction healed the patient of his fever and inflammations, and the juice rescued the patient from snake venom. Therefore, it could be assumed that the concoction made from the herbs might consist of metabolites having antimicrobial properties, and the juice of the leaves might consist of chemical/metabolite that had antivenom properties. Now again, let us visualize a group of scientists walking inside the same village, talking to this old wise man, collecting these herbs, and returning to their respective laboratories, where they try to screen these herbs for the presence of active compounds having antimicrobial or antivenom properties using modern technologies. This whole procedure of exploring biologically important/useful compounds from natural resources lays down foundations to the science of "bioprospecting." The former half of our visualization could be considered as "traditional bioprospecting," and the latter half of it could be considered as "modern bioprospecting." Traditional bioprospecting can even be traced back to as old as the bronze age. In 1991, a 5300-year-old corpse of an iceman "Otzi" was discovered in the Tyrolean Alps and was found to have a whipworm (Trichuris trichiura) infection. Surprisingly he was already equipped with the corresponding anthelmintic medicine, which is the fruiting body of the fungus Piptoporus betulinus [1, 2]. Thus, the utilization of natural resources for the interest of humans is as old as humankind itself, and what we follow today is just a modern and sophisticated version of this science.

The term "bioprospecting" was initially described by Reid et al. [3] as the science, where biological systems are screened for novel components that are of industrial, commercial, or scientific value. It includes the hunt for biological products that possess characteristics interesting to humankind. These characteristics could be considered to have great potentials in the field of therapeutics, agriculture, cosmetics, etc. Although the utilization of the biologically active properties of plant/animal extracts for various purposes was seen even before thousands of years, bioprospecting as a science for commercial and economic gains was introduced and progressed in and around the twentieth century. In 1958, vinblastine and vincristine, two therapeutic agents for cancer, were developed from the rosy periwinkle plant in Madagascar. These therapeutic agents were researched and manufactured by the company Eli Lilly with cues from the local shaman spiritual herbalists [4]. Further, prospecting in the wild has warranted many therapeutic agents, such as antibiotics and several other anticancer drugs. The modern biochemists and pharmacologists have been busy seeking ways to block or enhance the function of a target protein molecule for a cure to a particular disease. The classical combinatorial chemistry has its limits in the synthesis of new compounds when it comes to the exceedingly large and diverse number of the target proteins that are being identified. The diverse and continuously evolving structures of the natural products of Mother Nature may be a possible solution to these problems. Even as the rational drug designing with the help of combinatorial chemistry is becoming more important, natural products have been valuable for pharmaceutical companies owing to their wide structural diversity and their excellent adaptation to biological active structures [4]. A fast exploration of any medicine cabinet or a cosmetic shop directly indicates the share of bioprospecting natural products, by astute businessmen in building the global economy.

Chemicals, genes, and designs are the three major sources of motivation that biodiversity extends to contemporary scientists. Thus, the science of bioprospecting finds its applications with respect to these three domains and are called chemical prospecting, gene prospecting, and bionic prospecting respectively.

1.2.1 Chemical Prospecting

Nature and natural resources are a combination of diverse and repeatedly evolving systems that give rise to varying chemicals. The major defense mechanisms of the herbivores rely mainly on the chemicals synthesized by the plant [5, 6]. Communication, intraspecies and interspecies competition, attraction toward opposite sex, and pollination are also based to a great extent on chemistry and have accorded to the development of diversity [7, 8]. The scan of nature by humans for such useful chemicals has been termed as "Chemical prospecting" by Thomas Eisner [9], who in subsequent years had been tirelessly busy promoting it [10]. Although humans have been busy creating novel and diverse chemicals in the laboratory for different purposes, the contribution of the chemical diversity present in nature toward these creations has been admirable. The extent of chemical diversity found in nature has always found a role in our day-to-day lives either as a lead molecule inspiring the chemists to create certain novel compounds or the lead molecule used as common drugs. There have been many examples of natural compounds used as therapeutic agents, which later have been synthesized commercially and have led to economic gains. Most of these natural compounds were derived from either wild plants, animals, or microorganisms. Snake venom, for example, has also been a source of a number of neurological drugs. The peptides in the venom of snake Bothrops jararaca were responsible for the antihypertensive medicines enalapril and lisinopril [11]. This peptide in the snake venom was responsible for the inhibition of an enzyme in the human blood, which converts the enzyme angiotensin I to a hypertensive form angiotensin II. The analysis of the bioactive compounds present in the snake venom finally led to the formulation of antihypertensive drugs captopril and enalapril, etc. The nonsteroidal anti-inflammatory drug, diclofenac, was derived from the lead molecule salicin obtained from the bark of willow tree Salix sp. [12]. The antiviral drug vidarabine and anticancer drug cytarabine were obtained from the marine sponge [13]. Similarly, the antiviral drug acyclovir was prepared using prior knowledge of cytosine arabinoside, which was isolated from a Florida sponge [14].

The screening of the natural chemicals can be either random where materials are collected from random plants and animals or is based on the traditional knowledge, where materials are collected from plants and animals with a known function. These materials are subjected to extract preparation and bioassays to discover the bioactivity. The bioactives are further extracted and purified using automated systems. Many of the modern pharmaceutical industries have become huge economic giants, utilizing the ethnobotanical richness and diversity of nature for drug explorations.

1.2.2 Gene Prospecting

The advent of modern gene technology offers many opportunities for the selection and propagation of efficient traits. There have been many products from nature...