Proteins as a source of nitrogen for tobacco plants grown in vitro

Nitrogen (N) belongs among necessary elements for plant growth and development. In the past attention was paid mostly to the inorganic forms - nitrate and ammonium. In soil N is also present in organic forms, including proteins, for which plants could compete with soil microorganisms. Recently two ways have been considered - the hydrolysis of proteins by secreted proteases and endocytosis of native proteins, possibly their confluence. Tobacco plants were grown in vitro under sterile conditions in modified Murashige-Skoog medium with casein as the only source of N (CAS), decreased concentration of inorganic forms of N (AD) or in complete Murashige-Skoog medium as control plants (MS). After the 12 weeks growth, the standard growth parameters were measured. The CAS plants were able to grow without inorganic N, and protein content in the leaves was higher than in other experimental plants. Proteomic analysis documented differences in protein expression in plant roots in the dependence on the form of N. In total 185 proteins were identified, 75% of proteins were less and 14% more abundant in the CAS plants. The uptake of casein conjugated with fluorescein was followed and the proteolytic activity was analyzed by confocal microscopy. Among proteins secreted from roots to the medium aspartic protease..