**2. Metabolism**

the compounds contained in plants. In this field, various techniques have been developed, ranging from the preparation of the plant tissue sample to sophisticated techniques for the elucidation of organic structures. The search for new products for the pharmaceutical and agrochemical industries is an ongoing process that requires continual optimization [1]. Previously, the screening of 10,000 natural products resulted in one commercial product. In the advent of combinatorial chemistry, this relationship changed. Presently, the screening of 100,000 structures day−1 from combinatorial chemistry together with the natural products screened yields less than one commercial product year−1 (F. Hansske, pers. comm.). Its development takes approximately 12 years and costs ~\$350 M [2]. Considering that 6 out of 20 of the most commonly prescribed medications are of fungal origin [3] and only ~5% of the fungi

Endophytic fungi, a polyphyletic group of highly diverse, primarily ascomycetous fungi defined functionally by their occurrence within asymptomatic tissues of plants, are found in aboveground tissues of liverworts, hornworts, mosses, lycophytes, equisetopsids, ferns, and seed plants from the arctic to the tropics, and from agricultural fields to the most biotically diverse tropical forests. Their cryptic lifestyle, ubiquity and richness within individual plants, coupled with emerging evidence of their often overlooked ecological importance, have inspired growing enthusiasm regarding these little known fungi over the past four decades. In particular, David Hawksworth's much discussed estimates of fungal diversity at a global scale [4, 5] engendered tremendous enthusiasm for understanding endophyte diversity. Comprising interactions that range from mutualism to antagonism, fungal symbioses with plants are key determinants of biomass, nutrient cycling and ecosystem productivity in terrestrial habitats from the poles to the equator [6, 7]. Most plantassociated fungi catalogued to date have been recognized because of the fruitbodies they produce in association with their hosts (e.g., plant pathogens, mycorrhizal fungi). Yet plants in all major lineages, including liverworts, mosses, seed free vascular plants, conifers, and angiosperms, also form cryptic symbioses with fungi that penetrate and persist within healthy aboveground tissues such as leaves. Foliar fungal endophytes (i.e., endophylls or mycophyllas) are a fundamental but frequently overlooked aspect of plant biology: all plant species surveyed thus far harbor one or more endophytic symbionts in their photosynthetic tissues [8]. Plants live in association with microorganisms with different levels of interaction. This assumption stimulates insights on plant microbiome, intended as the collective genome of microorganisms living in contact with plants [9], and new concepts in plant evolution have been developed considering a basic role of the associated fungal endophytes [10]. Regarded as an underexplored niche of chemo diversity [11], endophytic fungi have a recognized ability to produce bioactive compounds which may play a role in plant protection against pathogens and pests [12, 13]. Colonization by endophytes may offer significant benefits to their host plants by producing various metabolites that protect against pathogen attack, promote plant (or vegetative) growth, improve crop yields, show herbicide activity and induce resistance. Fungal natural products are currently used in agriculture as active ingredients of different bioformulates [14] and several endophytes are known to have anti-insect properties [15]. Although bioinsecticides currently occupy only a small amount of the market,

have been described [4], fungi offer an enormous potential for new products.

26 Phytochemicals - Source of Antioxidants and Role in Disease Prevention

these compounds are very interesting and their use is constantly increasing [16].

In 1991, researchers began studying the microbial endophytes of the Northwest Pacific yew tree *Taxus brevifolia*, in search for a fungus or bacterium that could produce paclitaxel in de Metabolism is a set of chemical reactions carried out by the cells of living beings, to synthesize complex substances from simpler ones, or to degrade complexes and obtain simple ones [25]. Plants, autotrophic organisms, have two metabolisms, the primary metabolism present in

**Figure 1.** The metabolism of plants.

all living beings and a secondary metabolism that allows them to produce and accumulate compounds of diverse chemical nature (**Figure 1**).

Most of the carbon, nitrogen and energy ends up in common molecules to all the cells, which are necessary for their functioning and the organisms they belong [26]. These are amino acids, nucleotides, sugars and lipids, present in all plants and performing the same functions. They are called primary metabolites.

**3. Phytochemistry**

**Figure 2.** Production of secondary metabolites.

be in the optimal conditions to be analyzed.

• Determination or quantitative assessment.

the solvent that will be used for that purpose.

• Separation and isolation of them.

Phytochemical research of a plant includes several aspects:

• Extraction of the compounds to be analyzed from a sample or specimen.

• Identification and/or characterization of the isolated compounds.

• Investigation of the biosynthetic routes of a certain molecule.

The discipline whose main objective is the study of the chemical constituents of plants is Phytochemistry. The study of such compounds includes: their chemical structures, metabolism (biosynthesis and degradation), natural distribution, biological function, extraction and qualitative-quantitative evaluation. Before starting, any phytochemical analysis is important to have an adequate preparation of our plant material. A practical and simple way of stabilization is by heat treatment, applied, for example, in an oven at a reference temperature of 60°C until the samples reach constant weight; this way, we will make sure that our compounds will

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In the extraction and purification of organic compounds through the use of solvents, usually follows certain rules based on structural analogies between the substance to be extracted and

Plants allocate a significant amount of assimilated carbon and energy to the synthesis of a wide variety of organic molecules, that do not seem to have a direct function in photosynthetic, respiratory processes, nutrient assimilation, solute transport or protein synthesis, carbohydrates or lipids, and which are called secondary metabolites (also called by-products, natural products) [27].

Secondary metabolites are characteristic of superior plants. The essential characteristic of the superior plants is that they possess flower and, consequently, seeds. Its reproductive mechanism is different from that of the inferior ones. They are also called spermatophytes because their reproductive organs are visible and they are subdivided into gymnosperms and angiosperms.

Natural products have biological properties, and they are characterized by their different uses and applications as medicines, insecticides, herbicides, perfumes or dyes, among others. The biosynthesis of secondary metabolites is usually restricted to specific stages of plant development and periods of stress [25]. Some plant cells produce important secondary metabolites of the interactions of the plant with the environment (protection against predators, pathogens or environmental stress) or some related to the reproductive mechanism of the plant (attraction of insects for the promotion of pollination) (**Figure 2**).

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**Figure 2.** Production of secondary metabolites.
