DIFFERENCES IN NITROGEN-METABOLISM BETWEEN CULTIVARS OF TOMATO AND PEPPER DURING EXPOSURE TO GLASSHOUSE ATMOSPHERES CONTAINING OXIDES OF NITROGEN

Activities of two enzymes involved in this pathway have been investigated in two important horticultural plants exposed to atmospheric levels of nitric oxide (NO) or nitrogen dioxide (NO//2) commonly found during commercial cultivation under glass. In most cultivars of tomato, the response to NO//x has been shown to be a significant induction of nitrite reductase (NiR) but in leaves of sweet pepper, exposure to either of the two gases reduced the level of in vitro NiR activities even though an accumulation of amine compounds in the tissue suggested that the rates of nitrate reduction had increased in vivo. No effect on nitrate reductase (NaR) activity of either of the two gases was detected in pepper although an increase in NaR activity in the presence of NO//2 was shown by one tomato cultivar. Additional study results are discussed.