Flux of singlet oxygen from leaves of phototoxic plants

Detached leaves of Zanthoxylum americanum and Pastinaca sativa, plants known to produce phototoxins, generate singlet oxygen when illuminated by a xenon arc lamp that simulates sunlight. Other species tested did not produce detectable amounts of singlet oxygen. Calculations of the rate of production of singlet oxygen indicate a flux of up to 4×10¹² molecules cm^-1s^-1. This level is sufficiently high to induce damage in the cells of organisms near the leaf surface. Photodynamic action may thus provide for plants an evolutionary advantage in the form of preemptive protection against predators without tissue loss.