Variable patterns of antioxidant protection but similar ethene emission differences in several ozone-sensitive and ozone-tolerant plant selections

Six pairs of O₃-sensitive and O₃-tolerant cultivars, clones or populations of different plants (tobacco, plantain, clover, radish, poplar and loblolly pine) were taken through identical but short episodic exposures to O₃ in a controlled-environment fumigation system. Emissions of ethene and concentrations of polyamines, total phenols and ascorbate as well as levels of reduced glutathione and ascorbate in fumigated and clean air controls were determined in these various cultivars, clones and populations. A large number of significant differences were detected between the various sensitive and tolerant pairs, but it is clear that different sequences of response involving these parameters occur in these various plant pairs to account for their individual O₃ sensitivity or tolerance. Some O₃-tolerant plants have increased polyamines, others total phenols and some appear to be able to form reduced ascorbate and glutathione more rapidly. In the case of ethene emissions, however, all O₃-sensitive selections produce more ethene when fumigated while O₃-tolerant ones either reduce their rates of emissions below those of clean air-grown controls or at least keep them at the same level.