Usefulness of Fluorescent Probe Prodan To Gain Insight into the Polarity of Plant Cuticles.

Plant cuticle is a complex mixture of hydrophobic components that controls the uptake of pesticides by plants. Although the transport of lipophilic molecules across the cuticle has been intensively studied, development of tools to measure the cuticle polarity has received little attention. We developed a rapid and simple analytical method to evaluate the polarity of cuticles in situ. This method uses Prodan, 6-propionyl-2-(dimethylaminonaphthalene), a medium-sensitive fluorescent probe. Tests on model surfaces with varied polarity (i.e., wax paraffin, polyethylene, C18) were carried out to test the feasibility of the measurement and to optimize the application of Prodan. Moreover, on the basis of the Kamlet-Taft solvatochromic comparison method, a relationship between the emission characteristics of Prodan and the number of carbon atoms in primary alcohols mimicking the solid medium was established. After optimization, the method was validated on three natural plant cuticles (leaf of Zamiifolia, skin of green pepper, and skin of white grape).

Photolysis of natural ß-triketonic herbicides in water.

The fate of four natural ß-triketones (leptospermone, isoleptospermone, grandiflorone and flavesone, pKa = 4.0-4.5) in aqueous solution, in the dark and upon simulated solar light irradiation was investigated. In anionic form, ß-triketones undergo slow dark oxidation and photolysis with polychromatic quantum yields varying from 1.2 × 10(-4) to 3.7 × 10(-4). Leptospermone and grandiflorone are the most photolabile compounds. In molecular form, ß-triketones are rather volatile. Polychromatic quantum yields between 1.2 × 10(-3) and 1.8 × 10(-3) could be measured for leptospermone and grandiflorone. They are 3-5 times higher than for the anionic forms. Photooxidation on the carbon atom bearing the acidic hydrogen atom is the main oxidation reaction, common to all the ß-triketones whatever their ionization state. However, leptospermone shows a special photoreactivity. In molecular form, it mainly undergoes photoisomerization. Based on this work, the half-lives of ß-triketones in surface waters should be comprised between 7 and 23 days.