Research projects:
Iron transport, storage and oxidative stress responses
In aqueous environments, the total iron concentrations are in the 0.1 -10 nM range. In the series of studies we have tracked the pathway of iron uptake and storage in cells of photosynthetic cyanobacteria. Our findings include:
- The elucidation of the molecular mechanism that transports iron, its control circuitry and its sources of reductive energy.
- Identification of intracellular storage complexes, their interactions and the effect of their function on oxidative stress.h
- Extension of the findings on the regulation of transition metal homeostasis to their evolutionary progenitors, the chloroplast
Mn bioavailability and the organization of the photosynthetic apparatus
Unlike iron, Mn is not considered as a limiting factor in either aqueous or terrestrial environments. In the surface waters of oceans and lakes, Mn concentrations are at the range of 1-100 nM. Nevertheless, we have found large scale changes in the form and function of the photosynthetic apparatus of cyanobacteria in this environmentally relevant concentration range. The acclimation to changes in Mn bioavailability includes:
- Effects on photosystem II activity. Being a Mn containing enzyme these effects where expected.
- In parallel with the effect of PSII, a decrease in the photochemical activity of Photosystem I was observed. The loss of activity was the result of two processes - loss of PSI core proteins and changes in the organization of PSI complexes. The sensitive range for changes in the organization of the photosynthetic apparatus overlaps with the range of Mn concentrations measured in natural environments.
Adaptations of photosynthetic organisms to extreme environments
Biological sand crusts represent one of the harshest environments in nature. Organisms inhabiting this ecosystem face frequent hydration/dehydration cycles, extreme light intensities, temperature and osmotic potential fluctuations. Crucial for survival in these habitats is the ability to sense diurnal changes in environmental conditions and rapidly activate metabolism and growth in the short periods when water and sufficient light intensity are available, but to turn metabolism off during desiccation. Studying such organisms is revealing new strategies for survival in extreme environments.
In a long term study of photosynthetic organisms inhabiting sand crusts we have identified two unique algae:
In a long term study of photosynthetic organisms inhabiting sand crusts we have identified two unique algae:
- A filamentous cyanobacterium that can withstand hydration/dehydration cycles. The photosynthetic apparatus of this organism can be completely shut down during dehydration or when exposed to high light. We are currently in the process of elucidating the biophysical nature of the changes in the reaction center of photosystem II that support these processes.
- A green algae, Chlorella ohadii, exhibiting remarkably fast photosynthesis and growth rates far exceeding any other known algal species. Beyond the study of the characteristics that allow this alga to perform so well, we are developing it as resource for algal biotechnology approa ches
Expending the scope of photosynthesis research using advanced physics and physical chemistry methodology
Photosynthesis research has a long history of cross-disciplinary research. In our work we strive to incorporate new ideas and methodologies from physical chemistry and quantum physics. We do so through collaborative interdisciplinary studies, which have yielded intriguing data and novel concepts to biological reserch:
- Probing the architecture of photosynthetic membranes (Collaboration with Uri Raviv, Institute of Chemistry). In this joint research we are identifying the forces that control the organization of membranes in vivo using solution x-ray diffraction techniques.
- Understanding the function of large assemblies of light harvesting antenna proteins (Collaboration with Yossi Paltiel, Applied Physics). In this project we have identified long range quantum coherent processes in antenna systems. These results shed new light on the amazing efficiency of photosynthetic antenna.