A third function still sometimes underestimated is the processing of extracellular proteins, regulating cell growth and development, occurring mostly in the cell wall. A second function that has been identified for certain proteases is pathogen defence, working in concert with other lytic enzymes such as lipases and collagenases. It is generally assumed that the main function of both microbial and plant-exuded proteases is nutrient cycling, making nitrogen from organic compounds available for consumption. While bacteria and fungi have long been known to excrete proteases among other extracellular enzymes, the knowledge of exudation of proteases by plant roots is more recent. Furthermore, proteases have been shown to occur in the rhizosphere. In focus of this study are proteases, hydrolytic enzymes cleaving peptide bonds which can be found in all cells and organelles of a plant body. While carbohydrates may constitute the bulk of root exudates, other components like acids, single ions, allochemicals and proteins are of no less importance for rhizosphere processes. Other models, however, suggest an even exudation zone surrounding the whole root system. Exudation rate and composition have been suggested to vary between root zones with highest rates in apical regions, declining towards older root parts. Exudation can occur by rhizodeposition (sloughing off of cells) and passive or active exudation mechanisms of single compounds.

Root exudation is a process of excreting substances from plant roots and assumed to be the main source of organic carbon in the rhizosphere. Both positive and negative biotic interactions in the rhizosphere are considered to be vitally mediated by root exudates, deeming them a focus in rhizosphere research. Various biotic interactions among plants and microorganisms occur in the rhizosphere, influencing fluxes between organic and inorganic nutrient pools, plant nutrient availability and plant health. It is considered as a dynamic system of interacting processes with major implications for climate and environmental changes in aspects of greenhouse gas emission, carbon sequestration and soil fertility management for sustainable agriculture. The rhizosphere is most concisely described as the soil influenced by plant roots.

Root primordia tomato plant