The role of cytokinins, ethephon, and chlorocholine chloride in the native proteolytic activity of forest soils

PURPOSE: Plant growth-promoting rhizobacteria (PGPRs) synthesizes and exports phytohormones which are called plant growth regulators (PGRs). These PGRs may play a regulatory role in plant growth and development. PGRs are organic substances that influence physiological processes of plants at extremely low concentrations. The objective of this study was to find out whether three PGRs, cytokinins, ethephon, and chlorocholine, have a stimulatory or inhibitory effect on the activity of native proteases in soil. MATERIALS AND METHODS: A revised methodology was used to determine soil protease activity, where TRIS-HCl buffer was replaced with demineralized water. This is described as native protease activity as its activity is not affected by chemicals. The aim was to approximate the protease response to cytokinins in the native soil environment. The native soil proteolytic activity was determined spectrophotometrically. RESULTS AND DISCUSSION: The present paper shows that cytokinin, ethephon, and chlorocholine chloride negatively affect the native proteolytic activity of forest soils with the exceptions of the organic and organomineral horizons of European beech (Fagus sylvatica L.) on a rendzic Leptosol. In addition, 6-benzylaminopurine stimulates the native proteolytic activity of the organic horizon of pedunculate oak (Quercus robur L.). A negative effect of cytokinins on the soil proteolytic activity can decrease the rate of organic matter decomposition. The results provide soil biochemists with an insight into the roles of rhizospheric substances on soil microbial activity. CONCLUSIONS: This work has shown that cytokinins and PGRs inhibit the activity of native soil proteases in most of the studied forest sites. Results describe the effect of rhizospheric compounds on the activity of soil microorganisms, with potentially significant implications for the nitrogen cycle in forest soils.