XVI International Botanical Congess

Digestion of protein in the rumen of cattle is generally regarded as a microbially-mediated process. Whilst this may be true for animals fed with conserved diets, we contend that plant enzymes contribute this proteolytic function in ruminants grazing at pasture. Ingested plant cells are largely intact on entering the rumen and will therefore respond to stress. The rumen is maintained anaerobically at 39?C, thus condeming the plant cells to eventual death. Our results suggest that within hours of entering the rumen plant cells embark on a form of programmed cell death similar to rapid senescence, including increased proteolysis associated with demobilisation of cell constituents. This suggests that much of the initial, rapid phase of proteolysis occurs before plant cells are degraded by celluloytic rumen micro-organisms. Excessive proteolysis in the rumen leads to environmental pollution and poor use of feed proteins but in the future it may be possible to optimize protein degradation in the rumen by plant breeding strategies.