Active ingredient uptake and translocation
The biological activity of a crop protection product is determined by its active ingredient, which may be formulated to improve handling, storage, application and bioavailability.
Bioavailability refers to the extent a substance or active ingredient becomes available to its intended biological target site, and is determined by active ingredient concentration at site of application, anatomic & physiological characteristics of the absorptive site and active ingredient solubility.
This course provides an insight into plant physiology and anatomy as barriers to active ingredient uptake and translocation, as well as active ingredient physical-chemical properties determining their uptake and translocation.
What are the main learnings/takeaways from this section?
Participants will understand that leaf physiology, anatomy and morphology are a function of a number of factors, including plant type and species, leaf age and environment, and influence how spray droplets and active ingredients interact with the leaf. The primary challenges to active ingredient uptake are the cuticular and cell wall barriers, while active ingredients may be translocated throughout the plant apoplastic or symplastic pathways, according to their lipophilicity and dissociation constants.
Depending on its intended use, a pesticide active ingredient may require an element of water solubility (hydrophilicity) to allow it to be transported and distributed within the plant, while having some non-aqueous solubility (lipophilicity), to allow it to permeate across biological membranes. To predict pesticide mobility (xylem & phloem translocation) in plants, we need to consider not only the solubility of the active ingredient (logP) but also its dissociation constant of the molecule (pKa), i.e. the charge of the molecules at physiological pH, as well as its molecular mass and melting point.