Inter-specific variability in protein use by two vegetable crop species

It is now well-known that plants can uptake not only inorganic nitrogen but also organic nitrogen compounds, mainly amino acids. However, soil proteins are the main pool of amino acids. According to our earlier papers, plants can get access to this source of nitrogen using root-secreted proteases, but the level of proteolytic activity of such root-secreted proteases is species-specific. Our aim was to compare the use of protein as nitrogen source by two vegetable crops having high (Allium porrum) or low (Lactuca sativa) level of activity of root-secreted proteases. Seedlings were cultivated on Murashige and Skoog medium (MS), MS medium without inorganic nitrogen, MS medium without inorganic nitrogen, but with casein in concentration of 0.01%, 0.1% or 1%. Fresh weight of shoot of A. porrum was the highest for seedlings growing on culture medium with casein, but shoots of L. sativa obtained the highest weight growing on the culture medium with inorganic nitrogen. Allium porrum seedlings obtained 15-fold higher proteolytic activity in the culture medium than L. sativa. Seedlings of A. porrum using such high activity of proteases secreted by roots could provide a substantial pool of amino acids for intensive growth. The current studies conducted on A. porrum and L. sativa suggest that the efficiency of protein use in nitrogen nutrition by plants is species-specific.