A root exudate is material released by a root into its immediate surroundings, including the rhizosphere. An exudate sample is different from a root-tissue extract: collecting released material asks what reaches the environment, whereas disrupting tissue also exposes intracellular contents.
One released compound can have a striking effect on another organism. In 1966, investigators isolated the germination stimulant strigol from cotton root exudates and demonstrated activity on a root-parasitic Striga. Chemical isolation linked a constituent of the released material to a measured developmental response.[ref]
Germination of Witchweed (Striga lutea Lour.): Isolation and Properties of a Potent Stimulant by C. E. Cook and others. Abstract: crystalline stimulant isolated from cotton root exudates and germination activity
For an original quantitative example, suppose a collection contains 30 nanomoles of a compound after 3 hours in contact with 2 grams of roots. With zero initial amount, no background contribution and no losses, the mean net appearance rate isThe assumptions matter: degradation, uptake, damaged-cell leakage or material from associated microorganisms could change the interpretation. A root-free collection blank and an explicit mass/time normalization help identify what was actually measured.
A germination assay on the same collection asks an additional question about biological activity. Amount released and potency per unit amount are separate properties; neither measurement alone specifies the other.
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