טכניון מכון טכנולוגי לישראל
הטכניון מכון טכנולוגי לישראל - בית הספר ללימודי מוסמכים  
Ph.D Thesis
Ph.D StudentRizshsky Ludmila
SubjectMolecular Analysis of Oxidative Stress-Response in Plants
DepartmentDepartment of Biology
Supervisors Professor Gadi Schuster
Mr. Ron Mittler


Abstract

An unavoidable consequence of aerobic life is the formation of reactive oxygen intermediates (ROI), by partial reduction of molecular oxygen. In the present work we studied the molecular response of plant to oxidative stress that occurs as a result of suppressing several antioxidant enzymes, i.e., internal stress, or as a result of a combination of environmental stresses such as drought and heat, i.e., external stress. We found that double antisense plants lacking the two major hydrogen peroxide-detoxifying enzymes, ascorbate peroxidase (APX) and catalase (CAT), activate an alternative/redundant defense mechanism that compensates for the lack of APX and CAT. Knockdown Arabidopsis plants with suppressed expression of the key water-water cycle enzyme, thylakoid-attached cupper/zinc superoxide dismutase (KD-SOD), were found to be suppressed in their growth and development. Although a number of transcripts involved in the defense of plants against oxidative stress were elevated in KD-SOD plants, and seedlings of KD-SOD plants were more tolerant to oxidative stress, these mechanisms were unable to compensate for the suppression of the water-water cycle in mature leaves. The molecular response of tobacco and Arabidopsis plants to a combination of drought stress and heat shock was also studied. Our study revealed a new type of defense response in plants. Our results highlight the plasticity of the plant genome and demonstrate its ability to respond to complex environmental conditions that occur in the field. Future studies should unravel whether ROI-producing mechanisms, such as NADPH oxidase, are also tied into this network and form a global response mechanism that regulates ROI function in cells.