Effect of leaf rust infection on chloroplast protein synthesis in leaves of barley (Hordeum vulgare cv. Triumph) : A thesis submitted in fulfilment of the requirements for the degree of Master of Science in the University of Canterbury [Lincoln College]

Abstract

In this work chloroplast protein synthesis was examined in 7 day old leaves of barley (Hordeun vulgare cv. Triumph) infected with 2 isolates of barley leaf rust (Puccinia hordei Otth PS and 65) . At 18 hours after inoculation a decrease in protein synthesis in the chloroplast accompanied the compatible reaction . In contrast, the incompatible reaction showed an increase in protein synthesis. Similar decreases in protein synthesis with compatible host-pathogen combinations and increases with incompatible combinations have been reported in the literature. This indicates a connection between host response to infection and protein synthesis. The protein synthesis inhibitors chloramphenicol and cycloheximide were used to distinguish between chloroplastically and cytoplasmically synthesized chloroplast proteins. The results indicated that most of the affected proteins were synthesized by the chloroplast. Analysis of the polypeptides on gradient SDS-PAGE gels showed major changes at 26 kd, 32 kd, 90-120 kd and 140-180 kd. The polypeptides in these regions are thought to be associated with photosynthesis and transcriptional and translational control. Such changes would explain observations of alterations in activities of the respiratory enzymes during the later stages of infection. This suggests that contribution of the chloroplast to host response at the early stages may be in the form of energy for production of resistance promoting factors.