Abstract
Nitrogen (N) is a limiting resource for plant growth and development. It is well-established that plants acquire N in the forms of nitrate and ammonium, even amino acids.
Nevertheless, N in the soil mainly occurs as proteins. The well-known paradigm that plants must rely on soil fauna for the breakdown of organic matter has been now challenged by many scientists.
We took a closer look at what happens with tobacco metabolism if grown in sterile in vitro conditions with casein as a sole N source. Proteolysis in the roots was followed with a fluorescent casein-fluorescein conjugate.
The activities of proteases, glycosidases and phosphatases were determined spectrophotometrically. We employed mass spectrometry and analysed the proteins of roots participating in N metabolism and root exudates of plants supplied with casein, and determined free amino acid, protein and mineral content.