Total and Rubisco Specific Proteolytic Activity during Dark Induced Senescence of Barley Seedlings

Six-day-old seedlings of barley (Hordeum vulgare L., cv. Hemus) were placed in darkness in order to induce senescence-like changes. The symptoms of senescence and the reversibility of the processes were followed by analyses of the content of leaf pigments, the levels of total soluble and Rubisco immunoreactive protein and total proteolytic activity with casein as a substrate. Rubisco specific degradation was estimated applying highly sensitive avidin-biotin ELISA method. The results do not support an involvement of metallo protease or ATP-dependent protease in Rubisco degradation in leaf extracts during dark treatment. It is suggested that enzyme modifications, aggregation and/or association with membranes may occur prior to Rubisco degradation.