Utilising organic nitrogen: Can plants produce protease enzymes from their roots?

Ms Lucy Greenfield1, Dr Paul Hill1, Dr Eric Paterson2, Prof Liz Baggs3, Prof Davey Jones1,4

1Bangor University, Bangor, United Kingdom, 2James Hutton Institute, 3University of Edinburgh, 4University of Western Australia, 

Nitrogen (N) is an important macronutrient for plant life. Plants can uptake N in the form of ammonium, nitrate, amino acids and oligopeptides. However, plants do not have direct access to the 40% of total soil N represented by proteins. To utilise proteins they first must be broken down into small peptides and amino acids by protease enzymes. The majority of soil proteases are produced by soil microorganisms to obtain their own carbon and N nutrition. Therefore, the ability of plants to secrete proteases to hydrolyse proteins into small peptides and amino acids would increase the availability of N to plants. In agricultural systems, a decrease in the reliance on inorganic N forms by plants would reduce the use of environmentally detrimental inorganic N fertilisers.

In a laboratory experiment, we investigated whether plant roots release protease enzymes. We also investigated whether protease released from roots were up- or down-regulated by the presence of inorganic N. Seedlings (Zea mays L. and Triticum aestivum L.) were grown in sterile, hydroponic conditions in an inorganic N nutrient solution or a zero N nutrient solution. Each week for one month, the nutrient solutions were analysed for proteolytic activity using a fluorescence aminopeptidase assay. At the end of the experiment, the root tip was excised and its in situ protease activity measured to determine whether root proteases are surface bound. We hypothesise that plants roots will not release exoprotease enzymes but instead remain plasma membrane bound with higher concentrations under the zero N treatment. Consequently, proteases present on the root surface allow the plant to utilise the protein fraction of soil without losing essential nutrients into the soil matrix.


Biography:

Lucy is a third year PhD student at Bangor University.

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