Plant Physiology - Musienko M. M. 2001

Plant Physiology and Biotechnology: Achievements and Development Prospects
Prospects for Solar Energy Conversion and Biotechnology

The Earth's plant cover has a mass of approximately 1800 billion tons of dry matter, which is equivalent to 30-10²¹ J. This corresponds to the known reserves of fossil energy. Through Photosynthesis globally, 173 billion tons of dry matter are synthesized annually. This is almost 20 times the global Energy Consumption of the 1980s. The period from 1968 to 1978 was characterized worldwide by unprecedented energy consumption, particularly oil, which ultimately led to the modern energy crisis. Consequently, in recent years, interest in developing renewable energy and raw material sources has been growing. Among biotechnological Methods of biomass-to-fuel conversion, the most widespread are the enzymatic production of ethanol and biogas (methane). It is estimated that The conversion of biomass into fuel and energy will soon account for up to 10% of global Energy Expenditure.

Bioenergy: Photoproduction of hydrogen. In the 1960s, it was established that isolated METABOLISM/14.html">Chloroplasts, in the presence of bacterial Hydrogenase and an artificial electron donor, produce hydrogen:

Organic compounds serve as the source of hydrogen, and Water photolysis is not observed. Later, in the 1970s, it was discovered that such chloroplasts, in the presence of hydrogenase but without additional electron Donors, evolve hydrogen under sunlight if ferredoxin acts as the electron carrier (Sasson, 1987). In this case, both Photosystems function. However, the hydrogenase isolated from Clostridium Bacteria proved to be quite sensitive to oxygen; therefore, the reaction was carried out in a nitrogen atmosphere using oxygen-scavenging components (glucose oxidase + glucose).

Such a mixture at pH=7.0 and a Temperature of 25 °C yielded 50 μ/mol of hydrogen per hour per 1 mg of chlorophyll for 6 hours. In some laboratories, this process lasted more than 10 hours. Oxygen was the main limiting factor.

This is a highly promising pathway for energy production because plant organisms have an abundant substrate (water), an unlimited energy source (the sun), and the final product—hydrogen—can be stored. It does not pollute the environment and has a high calorific value. The process is self-sustaining since the substrate (water) is regenerated after hydrogen evolution. To increase hydrogen yield, it is necessary to discover hydrogenases that are less sensitive to O₂. However, the duration of the process depends On the Stability of the isolated chloroplasts. If a stable system for hydrogen production via water photolysis is developed, then consuming 10⁶ J/m² of solar energy per day (100 W/m²), such an installation could produce 90 L of H₂ per 1 m² per day, or about 3 kg of H₂ per 1 m² per year with an energy content of approximately 400⁶ J.

In the future, research into the MOLECULAR MECHANISMS OF Photosynthesis, particularly water photolysis, will help elucidate their nature and pave the way for developing artificial systems capable of performing this process even more efficiently than plants themselves. The Development of a stable photochemical system that performs the function of the chloroplasts' second photosystem (i.e., water photolysis and the reduction of electron carriers) will be a major milestone in converting solar energy into hydrogen. Photoproduction of hydrogen, solar energy conversion, and the utilization of bioenergy hold exceptionally bright Prospects for the future.