Robotized time-lapse imaging to assess in-planta uptake of phenylurea herbicides and their microbial degradation

Two key physiological parameters of plant leaves, photosynthesis and transpiration, can be continuously monitored by, respectively, chlorophyll a fluorescence imaging and thermography. These non-contact techniques immediately visualize any local stress or treatment affecting either photosynthetic efficiency or water status. Photosystem II-inhibiting herbicides, including the phenylurea derivatives diuron and linuron, cause a marked increase in chlorophyll a fluorescence several days before appearance of chlorosis. Here, bioprotection through microbial degradation of linuron in the feeding solution of common bean plants (Phaseolus vulgaris L.) was monitored by the absence of an increase in chlorophyll a fluorescence in primary leaves. The different treatments and repeats were imaged sequentially at 2 h intervals using a robotized system with thermal, fluorescence and video cameras. Chlorophyll fluorescence imaging visualized the effect of linuron transported by the transpiration stream earlier than thermography. In addition, local effects and transport after topical application of diuron were recorded presymptomatically in tobacco (Nicotiana tabacum L.) and Arabidopsis thaliana (L.) Heynh. Thermal imaging clearly monitored localized stomatal closure, coinciding with the first increase in chlorophyll fluorescence, at the sites of diuron treatment. In conclusion, the robotized chlorophyll a fluorescence set-up permits fully reliable, early high-contrast visualization for bioremediation purposes.