Even more fun: leek (as well as other plants that have been researched by the same team eventually discovering rhizophagy) has accidentally been found to secrete proteases into culture medium.

Here we have N and C uptake.

Degradation of proteins by enzymes exuded by Allium porrum roots – a potentially important strategy for acquiring organic nitrogen by plants.

Adamczyk B¹, Godlewski M, Smolander A, Kitunen V.

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Abstract

Nitrogen is one of the crucial elements that regulate plant growth and development. It is well-established that plants can acquire nitrogen from soil in the form of low-molecular-mass compounds, namely nitrate and ammonium, but also as amino acids. Nevertheless, nitrogen in the soil occurs mainly as proteins or proteins complexed with other organic compounds. Proteins are believed not to be available to plants. However, there is increasing evidence to suggest that plants can actively participate in proteolysis by exudation of proteases by roots and can obtain nitrogen from digested proteins. To gain insight into the process of organic nitrogen acquisition from proteins by leek roots (Allium porrum L. cv. Bartek), casein, bovine serum albumin and oxidized B-chain of insulin were used; their degradation products, after exposure to plant culture medium, were studied using liquid chromatography-mass spectrometry (LC-MS). Casein was degraded to a great extent, but the level of degradation of bovine serum albumin and the B-chain of insulin was lower. Proteases exuded by roots cleaved proteins, releasing low-molecular-mass peptides that can be taken up by roots. Various peptide fragments produced by digestion of the oxidized B-chain of insulin suggested that endopeptidase, but also exopeptidase activity was present. After identification, proteases were similar to cysteine protease from Arabidopsis thaliana. In conclusion, proteases exuded by roots may have great potential in the plant nitrogen nutrition.

Also carbon-dioxide invades the root when dissolved in soil water. It can be taken up into the plant metabolism. I will discuss this in “carbon-microcycling” that should be available in the near future.

Best H