Amaranth Biology, Chemistry, and Technology

Octavio Paredes-Lopez

• Verlag: CRC Press
• Jahr: 2018
• ISBN:
  9781351086509
• Auflage: 1
• Thema: Biological Sciences
• Thema: Entomology

This book is devoted to amaranth, a plant to which 45 species are indigenous to the Mesoamerican region and 10 others originated in Africa, Asia, and Europe. Amaranth was the foundation of the extensive North and South American ancient civilizations and is still important in the agriculture of more recent Indian cultures. However, this plant nearly disappeared after the Spanish conquest. In view of the outstanding agronomic performance of the plant and the high nutritional value of the grain, it is now becoming an important crop in various regions of the world. Progress in the utilization of amaranth is directly related to scientific and technical information on its biological, physical, and chemical properties. Amaranth: Biology, Chemistry, and Technology begins with a chapter on the use of tissue culture, molecular biology, and genetic engineering techniques for crop improvement. The next few chapters deal with classical genetics, traditional plant breeding, and plant physiology. Following chapters review the properties of storage and leaf proteins, carbohydrates (especially starch), and seed oil. The potential of amaranth for new food products and popping is discussed, and commercialization and marketing of amaranth and its products are described. The book also emphasizes the outstanding nutritional properties of amaranth.

Chapter 1

Biotechnology for an Ancient Crop: Amaranth

E. Lozoya-Gloria

CONTENTS

I.	Introduction
II.	Tissue Culture of Amaranth
III.	Molecular Biology of Amaranth
IV.	Perspectives
References

I. INTRODUCTION

The potential of amaranth grain as food was recognized by old cultures in America; the Aztecs and Incas used it commonly until it was replaced, for reasons not well-known, by other vegetation such as corn and common beans after the Conquest. Although there are now some farmers dedicated to this crop, in many places it remains only as a familiar ornament in the backyard. Interestingly, the word “amaranth” means “everlasting” in Greek, which seems adequate for the history of this crop.¹

For some years now, amaranth has been “rediscovered” as a useful and promising plant, mainly because it looks like an interesting alternative to alleviate the increasing need for food by some countries of the Third World. Ironically, amaranth has been used as food for a long time by some of those countries, although it appears that the fast expansion of the desertic zones and the huge demographic explosion have been too much for any crop, including amaranth.

Some important efforts have been made in order to return to the use of amaranth and to increase the potential of this crop. In 1981, grain amaranth was selected as a priority for a research grants program by the Board on Science and Technology for International Development (BOSTID) of the U.S. National Academy of Sciences/National Research Council.

The suggested goals for this program were:

• Determination of the environmental conditions under which amaranth could be a nutritious and economical crop

• Identification of the best varieties and growing strategies for different regions

• Development of techniques to harvest and use grain amaranth in local settings

• Development of a base of information to support the expanded production and use of amaranth

Promising results have been obtained so that the Amaranth Newsletter was established,² and an international society on amaranth was proposed during the First International Amaranth Congress (Oaxtepec, México, September 22 to 28, 1991).

Amaranth production in 1990 was over 100,000 ha in the Soviet Union and was used mainly as a forage crop. Among other principal producers of grain amaranth are China, México, Guatemala, Perú, India, and Kenya.³

Although many species of amaranth are considered as opportunistic weeds and eventually used as food, there are three species which are consumed by humans as grains (Amaranthus hypochondriacus L., A. cruentus L. and A. caudatus L.). The grains (or seeds) are considered as pseudocereal and in addition to their use for food purposes, the pigments of leaves and grains of some species have helped the preservation of these plants by using them as ornamentals.

However, what is the attraction of amaranth? Why is it considered a “new crop”, in spite of its history? Among the principal attributes recognized to describe this plant as a “new crop” are³

• Has a high protein content (13 to 19 %)

• Has a high level of the essential amino acid lysine, in comparison to other grains like corn and rice

• Contains 1.5 to 3.0 times more oil than other grains which represents a high caloric content

• Can successfully grow in adverse environmental conditions such as drought, high temperatures, and saline soils

• Is a dicotyledonous plant using an efficient type of photosynthesis known as C₄ carbon-fixation pathway

• Is a crop with multiple uses such as food, forage, silage, green manure, and animal feed

• Has a promising potential in industrial applications, from cosmetics to biodegradable plastics

Currently, a big and important amount of work is being carried out, mainly on breeding. There exist already three major germplasm collections at the:

• U.S. Department of Agriculture (USDA) Plant Introduction Center, Ames, IA

• University of Cuzco, Cuzco, Perú

• National Bureau of Plant Genetics Resources, Simla, India

Some agronomical and biochemical aspects of this crop are described in the following chapters of the present work. These include updated information about environmental conditions, fertility, and location requirements for the cultivation of amaranth. In addition, important factors related to food applications, nutritional properties, and economic and social considerations are discussed. The current status of this crop in México, Perú, Kenya, China, and the U.S. is also analyzed.⁴

Although all this information is very valuable and useful, there are other aspects of amaranth which have not been so deeply investigated. These pertain to the potential of amaranth in biotechnology and even if some work is already being carried out, it is necessary to increase research efforts toward these aspects.

This chapter summarizes and discusses research already done regarding tissue culture and molecular biology of amaranth, as well as the future prospects for this crop in modern biotechnology.

II. TISSUE CULTURE OF AMARANTH

The advantages of plant tissue cultures for biotechnological applications and research have been described at large in many books and journals. In general, this is the path of choice for achieving many controlled manipulations on plants resulting in the selection of new and useful traits, such as resistance to chemicals/pathogens, micropropagation of “hardy” plants, and studies about the physiology, biochemistry, and genetics of specific cultivars, among others.

Particularly, tissue culture of cereals was a challenge for some time until the discovery of the right conditions for the establishment of embryogenic calli of different Gramineae.⁵

The first reported studies about tissue cultures of amaranth⁶ were done using A. cruentus, A. hypochondriacus, and A. tricolor. The authors reported that cell cultures from different explants of these species were easily established in several media (B5, MS, and White’s) using combinations of various plant growth regulators, such as 2,4-dichlorophenoxyacetic acid (2,4-D), naphthaleneacetic acid (NAA), kinetin (K), benzyl adenine (BA), and zeatin (Z). Appropriate calli for suspension cultures were obtained from leaf discs and, in some cases, embryo-like structures were observed. Using high concentrations of cytokinins, it was possible to get shoot regeneration from hypocotyl-derived calli. Regarding protoplasts obtained from leaves of amaranth, the same authors reported that neither cell-wall regeneration nor cell division were observed under the used conditions.

Later on, and using a different species of amaranth (A. paniculatus), the full regeneration of complete plants was reported. This was done with calli from hypocotyl segments which were induced to shoots formation in K and NAA; then, these shoots were rooted and transferred to soil.⁷

A recent paper⁸ using several varieties of four amaranth species (A. caudatus, three varieties; A. cruentus, four varieties; A. hybridus, two varieties; and A. hypochondriacus, eight varieties) reported on the successful (>95%) callus formation from hypocotyl and stem tissues in MS medium with a combination of either NAA plus benzylaminopurine (BAP) or 2,4-D plus K, for all assayed varieties. Callus growth was recorded, and results showed significant differences among varieties of the same species. In general, the NAA/BAP combination was more effective for callus growth in A. cruentus while 2,4-D/K was best for A. hybridus. A similar and scarce callus growth was observed for A. hypochondriacus and A. caudatus at any of the combinations of plant growth regulators used. Callus growth increased between 0.0215 to 0.1439 g fresh weight after 1 month of incubation, depending on the species and varieties. In contrast, only some of the calli of A. hypochondriacus and A. caudatus were more efficient at regenerating different organs such as shoots or roots. All regenerated shoots were able to form roots and, after transfer to pots, plantlets developed.

Another paper⁹ reported on the use of inflorescences of A. paniculatus to produce secondary inflorescences and plantlets in vitro. The immature inflorescences were placed in MS with several concentrations of kinetin; after four weeks, various responses were observed. At low concentrations (0.5 mg K/L), tissues formed calli; as kinetin content was increased (3 to 6 mg K/L), the results were secondary inflorescences; then leaves, shoots and calli were formed at 8 to 12 mg K/L; and finally leaves appeared at the highest levels (10 to 15 mg K/L). The average percent of floral buds responding per inflorescence was up to 10% independently of the kinetin concentration. If the buds forming leaves and shoots were kept in the same media, they formed calli at the base, with subsequent elongation but without roots. After transfer of these tissues to media with 12 mg K/L and 15% coconut milk, the authors observed the formation of roots and shoots. These plantlets flowered after 20 days in vitro without a special photoperiod.

All these reports have shown that although it is easy to get tissue cultures of amaranth (mainly calli), they are still recalcitrant species for plant regeneration, and, so far, there is not a reproducible procedure for this goal. The genotype of the different varieties of one species plus the endogenous auxin/cytokinin balance may play an important role. After these results, it is clear that more work should be done in this direction. Considering the results obtained in cereals, plant regeneration of amaranth does not seem impossible, and even some hints could be used from similar work already done on Gramineae.¹⁰

III. MOLECULAR BIOLOGY OF AMARANTH

Molecular biology techniques have been the most powerful tool for the transfer of specific and new genetic information into living organisms. Currently, the procedures of plant molecular biology are already established for many species and are used for research and applied purposes. The abundance and variety of commercial kits for RNA and DNA isolation, DNA cloning, cDNA and genomic libraries construction, directed mutagenesis, nonradioactive hybridization, and even a kit for plant transformation using the reporter gene β-glucuronidase (GUS) and which includes all necessary plasmids and other materials for gene detection and genetic expression analysis, talks about the availability of these methods in addition to the profitable aspects of their commercialization.

Through biotechnology and molecular biology, plants, as well as other living organisms, can be used either as receptors of genes introduced by genetic transformation (which will give those plants some specific traits or advantages over their wild variants) or as a source of interesting genes to isolate, characterize, and engineer for their reintroduction into the same plant or into different plants or organisms.

Current techniques for plant genetic transformation range from the initial one based on the natural genetic transformation mediated by the Ti plasmid of Agrobacterium tumefaciens to the biolistic or gene gun procedure.

With the Agrobacter...