Enzyme activity assays for nutrient solutions from closed irrigation systems

Abstract

Exo-enzymes degrading cell wall components of fungal pathogens may play a role in the biological control of plant diseases in hydroponic systems. Therefore, protease, cellulase and chitinase are of special interest. The main objective of this work was the development of enzyme assays suitable for the conditions found in nutrient solutions. Furthermore, inducibility of enzyme activities by amendment of organic substrates to nutrient solutions and the effect of storage on enzyme activities in nutrient solutions were investigated. Enzyme tests based on the rate of release of soluble dye-labeled fragments of chromogenic substrates were adapted for nutrient solutions and were evaluated as suitable for the purpose. Using Hide-Remazol Brilliant Blue R as substrate for protein degrading enzymes, a stable activity of protease for up to 16 h was found. In order to detect the activity of chitinolytic enzymes, Carboxymethyl-Chitin Remazol Brilliant Violet was utilized as substrate. Results indicated good performance of the test, although chitinase activity was not observed in the beginning but later in the crop season. Furthermore, an approach to detect cellulase activity using Carboxymethyl-Cellulose Remazol Brilliant Blue as substrate yielded satisfying results. Amendment of nutrient solutions with chitin and cellulose (1%) incubated for 3 days led to significantly increased activity of chitinase and cellulase, respectively. For all of the studied enzymes, storage at +2 °C did not affect the activity for at least 1 week. In contrast, storage of samples of nutrient solution at room temperature led to a rapid decrease in activity of chitinase and cellulase, whereas protease activity was negatively affected by freezing (−26 °C) the nutrient solution.