One of these tools employs the role of auxin phytohormone in regulating shade responses. The main bioactive auxin in plants, indole-3-acetic acid (IAA) regulates the response to SAS. We have developed a carbon nanotube-based nanosensor that specifically and directly measures IAA in plants. The nanosensor can be easily used across various plant species by simple application in leaves and other plant organs. The IAA nanosensor is not detrimental to the vitality of plant cells and can remain in the cells for extended periods of time, allowing for direct, real-time, and continuous measurement of IAA in plants. More importantly, we demonstrated that the IAA nanosensor can detect transient changes in IAA content during SAS. We also developed a new form factor for application of the IAA nanosensor by encapsulating nanosensors in silk microneedles to enable rapid, direct, and precise measurement of IAA in plant petioles, which shows strong response to SAS.
Another analytical tool uses the optical method of Raman spectroscopy to detect a decrease in carotenoid content in leaf blades and petioles of plants undergoing SAS. Carotenoid Raman peaks showed more remarkable response to SAS in petioles than leaf blades, which greatly corresponded to their morphological response under vegetative shade or high plant density. Most importantly, carotenoid content decreased shortly after shade induction but before the occurrence of visible morphological changes, allowing for the early diagnosis of SAS in plants. Taken together, the IAA nanosensor and Raman spectroscopy present species-independent analytical tools for direct and real-time measurement of SAS in plants.