A COMPARISON OF THE STRUCTURE AND FUNCTION OF THE HIGHLY HOMOLOGOUS MAIZE ANTIOXIDANT CU ZN SUPEROXIDE-DISMUTASE GENES, SOD4 AND SOD4A/

Two highly similar cytosolic Cu/Zn Sod (Sod4 and Sod4A) genes have bee n isolated from maize. Sod4A contains eight exons and seven introns. T he Sod4 partial sequence contains five introns. The introns in both ge nes are located in the same position and have highly homologous sequen ces in several regions. The largest intron (>1200 bp) interrupts the 5 ' leader sequence. The presence of different regulatory motifs in the promoter region of each gene may indicate distinct responses to variou s conditions. Zymogram and RNA blot analyses show that Sod4 and Sod4A are expressed in all tissues of the maize plant. The developmental pro files of Sod4 and Sod4A mRNA accumulation differ in scutella during sp orophytic development. RNA blot analysis of the respective Sod mRNAs i ndicates a differential, tissue-specific response of each gene to cert ain stressors. RNA isolated from stem tissue of ethephon-treated seedl ings shows an increase in the Sod4 but not the Sod4A transcript while there is no change in transcripts of either gene in leaves or roots. T here is differential mRNA accumulation between the two genes in leaf a nd stem tissue of paraquat-treated seedlings. Other agents that can ca use oxidative stress were also tested for differential expression of t he genes.