Foliar uptake of peroxyacetyl nitrate (PAN) by herbaceous species varying in susceptibility to this pollutant.

Abstract

Foliar uptake of peroxyacetyl nitrate (PAN) was measured by the gas exchange method on nine herbaceous species. Susceptibility to PAN was also examined in the tested species in order to seek correlations with the uptake rate of PAN. PAN was synthesized by the nitration of peracetic acid in n-tridecane. Uptake rate of PAN by the leaves was kept at a steady level during the 90 min light period, while in the dark it declined rapidly and reached almost zero within 30-45 min. This suggests that adsorption of PAN on to the surface of the leaves is very small and most of it enters the leaf through open stomata. Among the species tested, sunflower showed the highest rate of PAN uptake, followed by radish, tomato and spinach. Maize and soyabean exhibited the lowest rate. A highly significant correlation was observed between the rate ol PAN uptake and stomatal conductance among the tested species. Petunia was most susceptible to PAN, followed by radish and tobacco, but maize and peanut were tolerant. There was no significant correlation between the uptake rate of PAN and susceptibility to it among the species. A higher susceptibility of petunia to PAN was not characterized by a higher rate of pollutant uptake. These results show that the main factor determining the differences between species in susceptibility to PAN is not the amount that gains access to the tissues, but some internal metabolic processes.