I. Photo-oxidative Stress: biochemical and molecular mechanisms and strategies of stress tolerance
Subject Area: In green plants pigments and reactions of photosynthesis may mediate the production of reactive oxygen species (ROS) in light. ROS production is enhanced by CO2-deficiency and by various stress conditions leading to over-excitation of photosynthetic electron transport because NADPH cannot be sufficiently consumed by assimilatory reactions. ROS may damage membranes, pigments, proteins and nucleic acids. Finally "oxidative stress" may become lethal to plants. Therefore plants have evolved numerous protective mechanisms for the avoidance or removal of ROS ("antioxidants").
In spite of the presence of various protective systems certain proteins engaged in photosynthetic metabolism can usually not fully escape oxidative inactivation by light. The reaction center protein D1 of photosystem II (PSII) and the enzyme catalase which detoxifies the H 2O2 produced during photorespiration in the peroxisomes are inactivated and degraded in light and have to be replaced by de novo synthesis (repair). Their turnover increases with light intensity. Therefore, repair activities must be controlled and continuously adjusted to changing light conditions. De novo synthesis in order to repair both the D1 protein and catalase is regulated at the level of translation. Analysis of translational mechanisms controlling catalase synthesis represent a main topic of the present research of our group. When the capacity for repair is unsufficient, photoinhibition of PSII and a loss of catalase are induced in light. The loss of catalase further weakens antioxidative protection. As a consequence, photooxidative injury is enhanced and plant growth and yield decline under stress conditions, such as high light intensity, heat, low temperature, salt or exposure to pollutants.
However, several plants are able to acclimate to extreme environmental conditions and to avoid photooxidative injury. In order to analyze machanisms of stress tolerance, cold-hardened winter cereals (grown at low temperature) and alpine high mountain plants are investigated that have to survive very extreme unfavorable environmental conditions with a very short growing season. In an alpine high mountain plant (Homogyne alpina L.) a catalase of higher stability was found and its cDNA was cloned. This catalase cDNA is heterologously expressed in insect cell cultures in order to identify structures and sequences that are responsible for stability or light-sensitivity of catalases.
Subject area: Numerous plants are able to acclimate to low temperatures. Plants are protected against cold injury by the concerted expression of various cold-specific genes and the biochemical and metabolic changes resulting from the cooperation of their products. These include both proteins or enzymes that are engaged in protection against cold injuries and regulatory factors controlling the expression of such proteins.
III. Cellular Signal Transduction in Senescing Leaves and under Cold Stress (PD Dr. Th. Berberich)
Subject Area: In higher plants environmental and developmental changes lead to differential gene expression. Specific cellular signalling pathways determine which genes are switched on or off. Components like transcription factors, calcium ions and protein kinases are part of the signalling cascades. We have characterized factors which play a role in the cellular signalling in low-temperature stress and senescence in maize and tobacco. The function of these regulatory proteins will be examined in detail and further signalling molecules will be identified. Modern techniques in the field of molecular biology like DNA-protein and protein-protein interaction are employed. This research project is in close cooperation with Prof. Kusano at Tohoku-University in Sendai, Japan.
geändert am 27. Mai 2009 E-Mail: WebmasterM.Fauth@bio.uni-frankfurt.de