Nitrogen assimilation and metabolism in rusted leek leaves

Nitrogen assimilation and metabolism were examined in leek ( Allium porrum L.) leaves 12 days after inoculation with rust ( Puccinia allii ) and in healthy controls. Following infection, nitrate accumulated in rusted leaves, while ammonium content was reduced. A small increase in total nitrogen was observed in rusted tissues. Rust infection lowered the activity of nitrate reductase, substantially increased the activity of glutamine synthetase, but had little effect on nitrite reductase. An examination was made of amino acid breakdown, revealing a significant increase in glutamic acid degradation in rusted leaves. Ammonia production was enhanced following infection. The possible mechanisms underlying these alterations in nitrogen metabolism are discussed.