Abstract

UV-B radiation has negative effects on biologically active molecules in plant tissues. One such molecule is the nitrate reductase (NR) enzyme responsible for the reduction of nitrate to nitrite by means of NADH or NAPDH as reducing substrates. Environmental factors, such as UV-B, have the ability to alter the phenotypic response of effected loci. Quantitative traits are those that are affected by many genes and environmental factors, and the genes responsible for variation are called quantitative trait loci.

This study was undertaken to determine the location of stress-induced QTLs in maize. An experiment was set up using 30 recombinant inbred lines, of the B73xMo17 parental cross, as the testing population. Replicates of 6 seeds per line were used for both the control and the UV samples. UV was applied for 5 days, for 2 hours a day, and then all seed samples were harvested on the 5^th day. The control plants did not receive any UV. An assay solution was applied to the tissues to interact with the enzyme, and absorbance of the solution was taken to determine nitrogen concentration. An increase in absorbance correlates to an increase in nitrogen, and therefore an increase in NR activity. ANOVA and composite interval tests, with permutations, were run on QTL Cartographer for both UV and control populations. It was found that there were QTLs present for both control and UV, but that the chromosomal locations were not the same for the two conditions. Since all gene loci are not expressed in each environment, this shows that regulatory control is acting on these gene loci.