plant biotechnology

Biotechnology is a scientific discipline with focus on the exploitation of

Metabolic properties of living organisms for the production of valuable products

of a very different structural and organizational level for the benefit of

Men. The products can be the organisms themselves (i.e., biomass or parts

of the organism body), products of cellular or organismic metabolism (i.e.,

enzymes, metabolites), or products formed from endogenous or exogenous

substrates with the help of single enzymes or complex metabolic routes. The

organisms under question vary from microbes (bacteria, fungi) to animals

and plants. In addition to intact organisms, isolated cells or enzyme preparations

are employed in biotechnology. The possibility to submit the producing

organisms or the cellular systems to technical and even industrial

procedures has led to highly productive processes. The products of biotechnology

are of importance for medicine, pharmaceutical sciences, agriculture,

food production, chemistry, and numerous other disciplines.

Biotechnology receives the necessary scientific and technical information

from a considerable number of disciplines. Cell biology, morphology

of the employed organisms, biochemistry, physiology, genetics, and various technical fields are major sources. In the last two decades, molecular biology

and gene technology have substantially contributed to the spectrum of scientific

disciplines forming biotechnology. As is always true for progress in

natural sciences, it is especially true for biotechnology that more rapid development

and gain of higher standards depend on the improvement of

methods.

In the historical development of biotechnology, microbes have been

used preferentially. They still offer an extremely rich potential for biotechnological

application. Animal systems and their cells are also valuable

systems, especially in view of the very costly products (i.e., antibodies,

vaccines). Although much later in the chronological process, plant biotechnology

has made an impressive development in gaining basic and applicable

knowledge as well as in establishing production processes. It is therefore

justified to speak of an emerging field.

A LONG HISTORY TO REACH A HIGH STANDARD

In each ecosystem plants and other photosynthetically active organisms are

responsible for primary production, which provides the energetic and nutritional

basis for all subsequent trophic levels. The extremely high ability of

plants to adapt to all kinds of environmental conditions and ecosystems has

led to an extremely wide and differentiated spectrum of plants. Since ancient

times higher plants have formed the main source of food for men, and

therefore, concomitant with early phases of settlements and agriculture, men

started to establish and improve crop plants. Archeological evidence has

clearly shown how long well-known crop species (i.e., maize, cereals, legumes)

have been grown, modified by selection, and thus improved in quality

and yield. Plant breeding is indeed an old art that has been continuously

developed in efficiency and scope. Quite typical for quality breeding of, for

instance, cereals is the long procedure required (sometimes decades) to reach

particular genotypes and to cross in specific genes or traits.

An interesting achievement in breeding of wheat is characterized by

the term green revolution, in which (around 1950-1960) wheat genotypes

from many different countries were used successfully on a very large scale

to breed high-yielding and durable lines. For many countries such new varieties

were a very great improvement for their agriculture.

Another important goal in breeding improved crop plants is the often

achieved adaptation to unfavorable environmental conditions (i.e., heat,

drought, salt, and other cues). Although good results have been obtained,

such efforts will undoubtedly remain in the focus of future efforts. Better

insight into the physiology, biochemistry, and chemical reactions as well as the gene regulation of the endogenous adaptation and defense mechanisms

that plants can express will contribute to these objectives. Gene technology

will be an essential component in these efforts.

Another characteristic feature of the long-term breeding of cereals,

potatoes, or vegetables is the fact that during the long periods the shape and

the outer appearance of the plants have changed so much that the original

wild types were either lost or no longer easily identified as starting material.

A typical example is corn. Modern agricultural crop plants are also bred for

very uniform physical appearance, time of flowering, and maturity so that

harvest by machines in an industrial manner is possible (examples are cotton,

maize, and cereals). It is a feature of our high-yielding agriculture that all

possible mechanical techniques are being employed.

Very precious treasures for future agriculture and for plant biotechnology

are the gene banks and the International Breeding Centers, where

great numbers of genotypes of crop plants are multiplied and carefully preserved

for long periods of time. Such "pools of genes" represent the basis

for sustainable development and allow future programs for improved adaptation

of plants to human needs. Fortunately, the understanding has gained

ground in recent years that in addition to crop plants all types of wild plants,

in every ecosystem, must be preserved because of the genetic resources to

be possibly exploited in the future.

An interesting development in itself, with a long history and remarkable

contributions to culture and art, is the numerous and sometimes highly

sophisticated ornamental plants produced in many countries. Beauty of color

and flower shape were the guidelines in their breeding and selection. Rather

early in this development the value of mutagenetic reagents was learned,

and these ornamentals also served to shape the term of a mutant. Recent

biochemical studies with, for example, snapdragon, tulip, chrysanthemum,

or petunia and their flavonoid constituents clearly presented evidence that

the various flower colors can contribute to identifing biosynthetic pathways.

In connection with flower pigments, which are secondary metabolites,

it should be remembered that numerous other secondary constitutents of very

different chemical structures are valuable Pharmaceuticals. In many countries

knowledge of plants as sources of drugs has been cherished for long

times. Modern pharmacological and chemical studies have helped in the

identification of the relevant compounds. Such investigations are still considered

important objectives of plant biotechnology. In some cases extensive

breeding programs have already achieved the selection and mass cultivation

of high-yielding lines. In modern pharmacy, about 25% of drugs still contain

active compounds from natural sources, which are primarily isolated from

plants.

For a good number of years in the period from 1950 to 1980, plant

biochemistry and plant biophysics concentrated on elucidation of the photosynthetic

processes. The pathways of CO2 assimilation as well as structure,

energy transfer reactions, and membrane organization of chloroplasts and

their thylakoids were objectives of primary interest. Chloroplast organization

and molecular function of this organelle can be regarded as well-understood

fields in plant biochemistry and physiology.

The last three decades of the 20th century were characterized by very

comprehensive molecular analyses of chemical reactions, metabolic pathways,

cellular organization, and adaptative responses to unfavorable environmental

conditions in numerous plant systems. A very broad set of data

has been accumulated so that plant biochemistry and closely related fields

can now offer a good understanding of plants as multicellular organisms and

highly adaptative systems. From a molecular point of view, the construction

and the functioning of the different tissues and organs have become clear.

Numerous experimental techniques have contributed to this development and

some are typical plant-specific methods (i.e., cell culture techniques) with a

very broad scope of application.

A fascinating field of modern plant biochemistry concerns the elucidation

of the function and the molecular mechanisms of the various photoreceptor

systems of higher plants. Red/far red receptors, blue light-absorbing

cryptochromes, and ultraviolet (UV) light photoreceptors are essential

components of plant development (1). These systems translate a light signal

into physiological responses via gene activation. Quite remarkable, phosphorylated/

unphosphorylated proteins are the essential components of the

signal transduction system (1,2). Biotechnology will gain from this knowledge,

and highly sensitive sensor systems could possibly be constructed.

In the history of plant sciences and biotechnology, the recent development

of molecular biology and the introduction of gene technology deserve

emphasis. Isolation, characterization, and functional determination of

genes have become possible. Many plant genes were rather rapidly identified,

and the number is increasing at enormous speed. Promoter analyses

and identification of promoter binding proteins have decisively contributed

to an understanding of the organization and function of plants as organisms

consisting of multiple tissues and different organs. The phenomena of multigenes

and multiple enzymes in one protein family were further revealed.

Many different techniques in molecular biology and gene technology turned

out to be extremely valuable. Recognition of the biology of Agrobacterium

tumefaciens and application of its transferred DNA (T-DNA) system represented

giant leaps forward. In general, because of these modern gene technological

methods, plant biotechnology has grown into a new dimension

with putative future possibilities that can hardly be overestimated.