Cinnamic acid (CA) is a natural compound of plants that is involved in many biosynthetic pathways. CA exists in both truns- and cis- isomeric forms. The truns-form of CA is the more stable one, and can be converted to cis-CA by ultra-violet irradiation. Although cis-CA solution has been reported to act as a weak auxin, the vapor of cis-CA was found to induce epinasty of tomato plants similar to the effect of ethylene. This fact and the similarity of the structure and gaseous nature between the vapor of cis-CA and ethylene, led us to suspect that gaseous irradiated-CA might: (1) act as an ethylene analog; (2) induce ethylene synthesis in plant tissue; (3) act on the steps downstream of ethylene signal transduction pathway; or (4) act through an ethylene independent pathway. To test and d...[ Read more ]

Cinnamic acid (CA) is a natural compound of plants that is involved in many biosynthetic pathways. CA exists in both truns- and cis- isomeric forms. The truns-form of CA is the more stable one, and can be converted to cis-CA by ultra-violet irradiation. Although cis-CA solution has been reported to act as a weak auxin, the vapor of cis-CA was found to induce epinasty of tomato plants similar to the effect of ethylene. This fact and the similarity of the structure and gaseous nature between the vapor of cis-CA and ethylene, led us to suspect that gaseous irradiated-CA might: (1) act as an ethylene analog; (2) induce ethylene synthesis in plant tissue; (3) act on the steps downstream of ethylene signal transduction pathway; or (4) act through an ethylene independent pathway. To test and distinguish these possibilities, an antisense l-arninocyclopropane-l-carboxylic acid (ACC) synthase transgenic tomato plant (All) was employed. Our results show that the vapor of irradiated-CA failed to trigger the All fruit ripening, and it delayed ripening of banana fruit, indicating that the gaseous compound does not act as an ethylene analog. To further study the physiological functions of the vapor of cis-CA and differentiate it from ethylene, an ethylene-perception deficient tomato mutant (Nr) was used to circumvent ethylene disturbance. Unlike ethylene, the vapor of irradiated-CA was found to induce epinasty and the triple response of the ethylene-insensitive Nr mutant, as well as abolishing gravitropism of both wildtype and Nr mutant plants, indicating that the primary physiological functions of cis-CA and ethylene are different. In conclusion, our results suggest that the vapor of irradiated-CA triggers the plant epinasty and the triple response through an ethylene receptor-independent pathway.