In the contemporary science "Biotechnology" and its innovations are aiming at the problems of resources and environmental management. The term "Biotechnology" is schematically explained underneath:

Biological sciences + Chemical sciences = Biochemistry (1)

Biological sciences + Engineering = Bioengineering (2)

Chemical sciences + Engineering = Chemical engineering (3)

Biochemistry (1) + Bioengineering (2) + Chemical engineering (3) = Biotechnology

Selected areas in biotechnology for the management of renewable resources are briefly explained. The pressures of growing population in recent time has resulted in the exploitation of the forest resources to disastrous proportions. The increasing demand of biomass for fuel wood, timber, pulp and paper industry can no longer be met from the existing natural forests alone.

Biomass and Bioenergy

The tropical forests provide about 1,400 million m³ wood annually and out of this 1,200 million m³ is used as fuelwood Woody biomass is an important source of energy for rural communities. Population explosion in developing countries increased fuelwood demand and this has resulted in alarming deforestation. Although developments in remote sensing and satellite imaginary have improved measurement technique, estimates of tropical deforestation still vary widely. Rain forests are the most expensive comprising about 80% of the remaining tropical closed forests. The most recent estimates indicate that by the end of the 1980s the annual rate of deforestation was well over 8.4 M ha. However, other estimates put the global annual deforestation rate to as much as 15-22 M ha. For example, in the Brazilian Amazon region alone, different estimates put the total area deforested over the last decade between 25-60 M ha (5-12 % of Amazon land area) although, the present annual rate of deforestation may be only 2 M ha per year.

The greater usage and demand of biomass in developing, developed countries and as a whole in world and the search for renewable and alternate energy sources lead to energy plantations which gained global prominence. The objective of energy plantation refers to biomass production in carefully tended plantations using rapidly growing trees, preferably drought resistant, nitrogen fixers with coppicing ability for rotation of less than 12-15 years.

The annual photosynthetic storage of energy in biomass is eight times more that of energy use from all sources.This estimate clearly illustrates the immense potential of biomass resources if harnessed and managed sustainably. Biomass is the world's fourth largest source of energy but often is not accounted in official statistics (Hall and Rosillo-Calle 1991).

Several issues need to be examined if tree crops are to be treated as supplemental renewable sources The choice of tree species would depend on the end uses and the agroclimate of the area to be planted. Fast growing, short-rotation species with good pulping characteristics or calorific value are selected for paper-pulp or fire wood. Several million hectares of land all over the world come under the category of "Marginal or waste land" India lie waste because extreme salinity, acidity or due to other reasons. By a suitable choice of stress tolerant species, wasteland could be reclaimed for afforestation.

Biochemical conversion of biomass.

Acid and enzymatic hydrolysis of lignocellulose (agro waste) for co-production of liquid fuels and chemicals using conventional and biotechnological applications such as cell immobilisation

Microbial and enzymatic processing of biomass (lignocellulose) yields sugars fir further conversion to alcohol and other solvents of industrial importance. Any sugar or starch rich crop can yield ethanol through conventional yeast based fermentation or through upgraded cell immobilization methods, while anaerobic digestion of the sludge would produce methane (gaseous fuel) and stile/slurry (fertilizer).

Sweet sorghum, corn, cassava (tuber), sugar beet (tuber), jerusalem artichoke (tuber) etc. are the important energy crops.

The technique of cell immobilization was successfully employed in many bioreactors for production of liquid fuels and chemicals. Cell immobilization was quite advantageous with bacterial and yeast cells. Immobilization of cells and organelles is being rapidly developing for wider biotechnological applications. Sodium and calcium alginates, agar, polyurethane and polyvinyl forms etc. have been used in different bioreactors. The criteria for selecting a support material are that it should be non-toxic to the organism immobilized, possessing retention capacity, porous and can be prepared in specific particle size and shape.

Plant cell tissue and organ culture.

In vitro techniques are being increasingly applied to supplement conventional methods of vegetative propagation. The benefits of this technique include mass micropropagation, production of disease free stock and stress tolerant variants, and long term storage of viable germination. Thus, it is envisaged that the tissue culture technology is expected to meet this challenge.

By using in vitro techniques, a desired tree, selected on the basis of past performance could be propagated with time and genetic advantage compared to conventional methods. It is believed that tissue culture technology will have a great role in tree improvement through wide hybridization and induction of genetic variability which can be achieved in for less time and in largest numbers than has been achieved so far by conventional methods which it may supplement or replace

Considerable progress has been made in the area of plant tissue culture as they apply to non-woody, food and medicinal plants. Like wise temperate woody plants have responded favorably to in vitro manipulation. During the past one-decade several strategies and approaches have been elaborately dealt with by plant tissue culture practitioners. Currently, in vitro clonal propagation, an effective method for large-scale rapid multiplication of trees, is replacing the conventional methods of propagation. In majority of the cases plantlet regeneration has been reported, however, establishment of the plantlets in the soil is often difficult

Micropropagation of plants as it was advantageous over seed propagation: Each cell is "totipotent and can be cultured under aseptic conditions in a suitable culture medium having macro, micro nutrients, carbohydrates, vitamins and growth regulators etc. There are several advantages in using this biotechnological tools and are given below:

When conventional vegetative propagation is not possible, tissue culture has great potential. Standardized protocols for micropropagation works out to be cheaper in certain instances where the seed cost is exorbitant. Clonally propagated population would be more uniform when compared to seed produced plants. Spread of seed borne diseases can be avoided by borrowing cultured plantlets, since these are maintained under aseptic conditions. Tissue culture is the prerequisite for a number of genetic improvement and engineering studies which would enhance the biomass production.

Ex situ conservation of genetic resources.

A large number of plants are "threatened" or "endangered" mainly due to habitat destruction or due to excessive exploitation for their economic importance. In order to protect such endangered or threatened plants and to increase their population, micropropagation methods were found to be quite useful. E.g. Orchids and a number of medicinal plants.

Development of disease/pest resistant plants.

Disease free and pest resistant plants have been developed to enhance bioproductivity. These has been accomplished involving tissue culture techniques and RFLP. (RFLP = Restriction Fragment Length polymorphism) mapping although time consuming appears to be a promising for genetic improvement. RFLP mapping depends on natural variation in DNA base sequence, DNA is digested with a restriction endonucleases. homologous restriction fragments of DNA which differ in "size" or "length" can be used as genetic markers to follow chromosome segments through genetic crosses) eg. Leucaena leucocephala (subabul). It is widely grown in biomass forestry for its multiple uses such as fuelwood production, fertilizer, fodder. In Philippines, the national electricity administration owns about 12,000 ha of L. leucocephala plantation to supply wood for "Dendrothermal projects" (about 100-1000s MW). Several of the cultivars of leucaena suffer from psyllid pest which devastated the plantations in several parts of the world.

Transgenic plants.

Polyploids can be produced from cultures by specific inhibitors of cell plate. Similarly by culturing anthers haploids can be developed. protoplast technology involving the isolation, purification of protoplasts, fusion and culture of the fused product on suitable media would lead to somatic hybridization. These methods are of special significance in plant breeding, genetics and molecular biology.

Saxena et al. (1999) indicated that metals like mercury, selenium, arsenic or chromium can be rendered harmless by either enzymatic reduction or by incorporation into less toxic organic/metal compounds. These processes occur in nature and can be enhanced by genetic manipulation of plants through introduction of genes coding for enzymes responsible for the underlying biochemical reactions. A well-known example of such manipulation is the transfer and expression of a modified bacterial Hg²⁺ reductase gene in transgenic Arabidopsis thaliana plants (Rugh et al. 1996). Plants containing this new gene were more tolerant to the presence of mercury, compared to plants lacking it. The transgenic plants reduced Hg²⁺ to elemental mercury, which is easily volatilized at room temperature. Rugh et al (1998) also examined the ability of yellow poplar (Liriodendron tulipifera) tissue cultures and plantlets to express modified mercuric reductase (merA) gene constructs. Bacteria possessing merA are capable of converting highly toxic, ionic mercury , Hg(II), to less toxic elemental mercury , Hg (0). Thus, expression of merA in trangenic plants or identification of plants ecotypicaslly expressing such genes would certainly be helpful for ecologically compatible remediation options. Similarly, some plants can also volatilize selenium .

Secondary metabolites for industrial and pharmaceutical use.

A number of secondary metabolites produced by the different cells in tissue culture (through suspension culture) are important in pharmaceutical and cosmetic industries. Examples: alkaloids, anthroquinones, anti-leukamis and antitumour agents (anticancer agents), aromatic compounds, cardiac glycosides, chalcones, enzymes, insecticides, lipids, napthoquinones, phenolic compounds, plant growth regulators, steroids, terpenoids, tannins and vitamins.

Non-conventional food and single cell proteins.

A number of microalgae have been cultured for their economic importance. Some of the notable taxa are:

Environmental protection and conservation.

Many plants and microorganisms like phytoplankton respond spontaneously for the pollutants of air, water and soil. Hence specific symptoms of these biota would help in identifying them as bioindicators of pollution. Several of the fresh water algae, macrophytes of aquatic ecosystems where a variety of heavy metals are accumulated and certain plants growing on mine refuse are known to show characteristic symptoms that would enable scientists to use them as markers of pollution, which would eventually help in pollution control

Phytoremediation [Anonymous 1997, 1998; Brooks 1998] is on the brink of commercialization and gaining considerable importance globally owing its success on several case studies in real world ecosystems. Variety of strategies are being followed for field remedial uses. For e.g. Constructed wetlands, reed beds and floating-plant systems are quite common for the treatment of various types of wastewaters.

Plants growing in contaminated and polluted terrestrial and aquatic ecosystems takeup a variety of xenobiotics and complex them in their parts. Thus help in environmental decontamination. Principles of phytoremediation are employed for the extraction of metals from metallic residues, reclamation of waste sites, decontamination of toxic residues and stabilization of mine tailings and spoils.

Table 1. Fundamental processes involved in phytoremediation of contaminated and polluted soils (After Wenzel et al 1999)

^a HM = heavy metals, MO = metalloids, HA = halides, RA = radionuclides, OR = organic pollutants; bold symbols are indicating the primary target pollutants
* Phyto exctraction includes phytomining.

Plant species which can accumulate high concentrations of heavy metals have been known for over one hundred years. However, until the last twenty years their potential went largely unnoticed by scientists. The term hyperaccumulation was first introduced by Professor R. R. Brooks, Department of Soil Science, Massey University, Palmerston North, New Zealand in 1977. The concept of hyperaccumulation and phytoremediation renewed interest, together with heightened environmental awareness and the discovery of the phenomenon in many more species has since stimulated research into a number of novel scientific and commercial uses. The underlying processed of phytoremediation include the removal of heavy metal pollutants from soils and waters, mineral exploration, the revegetation of degraded land and the exciting possibility of the commercial extraction of heavy metals from crop plants (phytomining).

Metal recovery and mining.

Bacteria such as Thiobacillus ferrooxidans and Acidophilium organovorum are capable of growing on acidic environment of copper ores. When the former is grown on acidic copper ores it releases the metal. These bacteria when grown on low grade ores by a process of recycling, the concentration of the copper becomes high due to leaching. The accumulated metal from the effluent is removed by precipitation or by electrolysis. Schizosachharomyces cerevisiae is difficult to grow in an environment suitable for the growth of T. ferrooxidans, however, useful for metal recovery from a solution under specific conditions. Similarly application of suitable microbes for recovery of precious metals like gold, silver, uranium and platinum may be feasible and economical.

Suggested reading

Anonymous (1997). Phytoremediation - Transcribed and edited from International Business Communications, Inc. 2nd Int. Conf. on Phytoremediation held in June 18-19, 1997 Seattle, Washington, USA.

Anonymous (1998) Phytoremediation - Transcribed and edited from International Business Communications, Inc. 2nd Int. Conf. on Phytoremediation held in June 22-25, 1998 Houston, Texas

Gavinlertvatana, P., Matheson, A.C. and Sim M.E.P. (1987) Feasibility study on tissue culture for multipurpose forest tree species. Winrock International-F/FRED. Bangkok. pp.59, 1987.

Mantell, S.H. Matthews, J.A. and McKee, R.A. (1985) Principles of plant biotechnology. An introduction to genetic engineering in plants. Blackwell Scientific Publishers.

Brooks, R.R. (ed) (1998) Plants that Hyperaccumulate heavy metals (Ed) CAB International. Wallingford, UK. 384 pages.

Anderson, C.W.N., Brooks, R.R., Stewart, R.B and Simcock, R. (1998). Harvesting a crop of gold in plants. Nature 395: 553-554

Prasad, M.N.V. (1997). Trace metals. In, Plant Ecophysiology (ed) M.N.V. Prasad. Wiley, New York, pp. 207-249

Prasad, M.N.V. (1998). Metal-biomolecule complexes in Plants: Occurrence, functions, and applications. Analusis 26:28-28

Prasad, M.N.V and J. Hagemeyer (eds) (1999) Heavy metal stress in plants - From molecules to ecosystems. Springer-Verlag, Heidelberg, Berlin, New York. Pp. xiii + 401

Raskin, I. (1995). Phytoremediation: a novel strategy for the removal of toxic metals from the environment using plants. Biotechnology 13:468-474

Rugh, C.L., Wilde, H.D., Stack, N.M., Thompson, D.M., Summers, A.O. and Meagher, R.B. (1996). Mercuric ion reduction and resistance in transgenic Arabidopsis thaliana plants expressing a modified bacterial merA gene. Proc Natl Acad Sci USA 93:3182-3187

Rugh, C.L., Senecoff, J.F., Meagher, R.B. and Merkle, S.A. (1998). Development of transgenic yellow poplar for mercury phytoremediation. Nature Biotechnology 16:925

Saxena, P.K., KrishnaRaj, S., Dan,T., Perras, M.R. and Vettakkorumakankav, N.N. (1999) Phytoremediation of metal contaminated and polluted soils, In: Heavy metal stress in plants - From molecules to ecosystems., M.N.V.Prasad and J.Hagemeyer (eds) Springer-Verlag, Heidelberg, Berlin, New York. pp. 305-329

Wenzel, W.W, Lombi, E. and Adriano, D.C. (1999) Biogeochemical processes in the rhizosphere: role in phytoremediation of metal-polluted sites. In: Heavy metal stress in plants - From molecules to ecosystems., M.N.V.Prasad and J.Hagemeyer (eds) Springer-Verlag, Heidelberg, Berlin, New York. pp. p. 273-303