ABSTRACT
The classical genetic studies utilized mutant biotypes that were resistant to one or more photooxidant stress. Superficially, one would expect that a plant possessing high levels of any mechanism that quenches active oxygen species should be tolerant of all photooxidant stresses. The constitutive or induced levels of a plethora of stress tolerance pathways, so common in the genetic studies, must have a yield penalty, both in ideal growing conditions and when only a photooxidative stress is applied, because too many genes are activated. The genetic analysis of crosses between resistant and susceptible biotypes/strains/crosses, correlated with measurements of a variety of stress protective mechanisms, together with the use of gene probes and engineering, could teach much more than can be learned without genetics. The types of photooxidant stresses a plant may encounter can arbitrarily be divided into acute and chronic. Interspecific differences in resistance to sulfur dioxide stress have been shown in a large number of species.
