Sensitivity Of Wheat Leaf Aconitase To Nitric Oxide And Hydrogen Peroxide

Nitric oxide (NO) and hydrogen peroxide (H2O2) had been considered to be important signaling molecules and natural products in the course of biological metabolism. In NO signaling pathway, aconitase was a major NO target or sensor, and the activities of aconitase were also known to be inhibited rapidly by H2O2 and other ROS in animals. It had been proved that signaling molecules, NO and H2O2, also exerted a number of physiological functions in plants. It was known that the activities of tobacco aconitase were inhibited by NO and H2O2, and H2O2 could also dramatically inhibit the activities of potato tuber mitochondria aconitase. In addition, tobacco aconitase gene (NtACOl) was cloned, and the deduced aminoacid sequences of which shared 61% identity with the human IRP-1 and its motifs involved in mRNA binding by IRP-1 were also conserved in NtACOl. But there were many problems which still remained unclear. For example, effects of NO and H2O2 on the activities of other plant aconitases, and whether plant aconitases were also sensors of NO and H2O2 in their signal transduction pathways or not et al.Our results indicated that exogenous NO donor, sodium nitroprusside (SNP), and H2O2 dramatically inhibited the activities of aconitase from wheat (Triticwn aestivum L.) leaves, when aconitase crude extracted from wheat leaves , or partially purified aconitase were treated with SNP and H2O2. Simultaneously, exogenous peroxynitrite (ONOO") derived from its donor 3-morpholinosydnonimine hydrochloride (SIN-1) and salicylic acid (SA) also inactivated aconitase from wheat leaves. Meanwhile, sensitivities of mitochondria aconitase isoenzyme varied obviously when mitochondria aconitase were treated with SNP, SA, H2O2 and SIN-1.Among these substances, H2O2 and SIN-1 showed greater inhibition to mitochondria aconitase isoenzyme.Furthermore, when wheat leaves treated with SNP and 3-amino-l, 2, 4-triazole (3-AT), a specific inhibitor of catalase (CAT) respectively, the endogenous H2O2 levels in detached wheat leaves increased while aconitase activities decreased depending on dose and time-dependent manners. Meantime, the levels of endogenous citric acid and H2O2 in undetached wheat leaves accumulated. The above results showed that NO could possibly inhibit aconitase activity indirectly through the action of H2O2 induced by NO in wheat leaves in addition to the direct inactivation of aconitase activity by NO.