Plant root systems can grow to be complex due to a variety of species and microorganisms existing in a common soil.
The contents of exudates and the amount of substance released is reliant on multiple factors, including the root system architecture,[1] presence of harmful microbes, and metal toxicity.
At sufficient concentrations, exudates are capable of mediating[clarification needed] both positive and negative plant-plant[2] and plant-microbe interactions.
One example of root exudation occurs when plants sense elicitors and prime[clarification needed] for a stress or defense response.
Quantifying how much photosynthetically fixed carbon is transferred to soil via plant root exudates is difficult, but 5% can be considered a rough estimate.
This is the act of releasing phytotoxins into the rhizosphere that can influence neighboring plant's growth, respiration, photosynthesis, metabolism, and water and nutrient uptake.
[8] The maize plant releases exudates to deter herbivore attacks from pest by reducing its leaf nutrient value and as well repressing its size.
These primary metabolites are thought to be primarily released through the root tip when the rhizosphere is negatively affected by stressors such as being nutrient poor.
[10] “The phloem unloads the primary metabolites through the plasmodesmata using both facilitated diffusion and pressure flow mechanics to push release at the root tip”.
[10] Another possible mechanism of release of exudates would be the plants ability to control “efflux of primary metabolites is controlled through distinct channels and carriers which in turn allow down regulation in response to gene expression and or post translational modifications” examples of such transporters are GDU, SWEET, and CAT transporters.
[9] While the study of primary metabolites still needs more work, the proposals displayed due seem to provide a logical explanation for the mechanism driving root exudation.
Secondary metabolites consist of a variety of small molecules, they are vast in the rhizosphere of plants and are used in numerous ways to benefit them.
[11] Specifically, these metabolites are released using the simplistic and apoplastic pathways and then finally “through the pores in the tips of root hairs where they bind to soil particles and organic matter”.
[8] Benzoxazinoids can change the relationship in fungal and bacteria for roots, as well as repress plant growth, and cause an increase in signaling for defensive purposes such as preventing herbivory attacks.
[8] The experiment also included mutant types of the wheat and maize families to test the lack of BX which is an activator for the response of signaling through Benzoxazinoids.
Despite being unable to move and flee like animals they are able to utilize other skills to gain nutrients, water, enact defensive mechanisms and possibly communicate with fellow kin.
[10] The mechanism powering this response has many proposals, one being that exudate secretion is controlled through redistribution of concentration gradients by manipulating the source-sink in plants.