Effect Of Spraying Urea On The Glycinebetaine Synthesis Metabolism Of Maize And Its Relationship With The Nitric Oxide Signaling Under Drought Strsee

The maize is the second largest food crop in China, and 60% of the corn growing regions are threatened by drought stress. Glycineglycinebetaine is an important organic substance in the cytoplasm of plants, and its effective accumulation is the important mechanism of plant response to stress. For to glycinebetaine synthesis plants, exogenous nutrient regulating substances, such as nitrogen nutrition application, can be further induced accumulation of the synthesis of glycinebetaine in plant. And it has become one of the technologies to improve plant stress capacity is widely used. Over the past few decades, for root application mechanism of nitrogen nutrition better research, and foliar application of urea nitrogen as a direct, efficient and fast control method, the stress regulation mechanism research is relatively lagging behind, especially physiological and molecular mechanism of synthesis and accumulation of glycinebetaine by exogenous urea nitrogen induced under the stress is not clear. In the present study, maize cultivar Zhengdan 958 was used to investigate the effects of exogenous applied urea on the GB synthesis and accumulation in maize to explore drought tolerance mechanisms. Main conclusions are as follows:1. The foliar urea application could significantly increased endogenous choline content of glycinebetaine precursor substrates in maize leaves under drought stress, promoted the synthesis and accumulation of glycinebetaine, and improved the corn leaf relative water content(RWC), to eased the drought stress to cause harm to the maize. The effect of adding urease inhibitor(catechol) in urea was more remarkable.2. The PEAMT(Phospho ethanolamine methyltransferase), CMO(Choline monooxygenase), BADH(Glycinebetaine aldehyde dehydrogenase) activities in maize leaves increased during the first 2 days in each treatment, and then decreased during the rest of the duration of exposure to drought stress. At the first 2 days, the three enzymes activity of urea and catechol treatment were the largest, next one was urea treatment. The results showed that urea could significantly improve the CMO, BADH and PEAMT activity of the key enzymes of glycinebetaine synthesis in maize under drought stress. The activity of spraying urea and catechol was further improved, and the increasing range of CMO and BADH activity was higher than PEAMT.3. The RT-PCR(Polymerase chain reaction) with specific primers was used to clone genes while semi-quantitative and real time PCR were used to analyze the expression of 3 genes, including PEAMT, CMO and BADH, at various times after urea spray. The results depicted that semi-quantitative RT-PCR and quantitative PCR have a high degree of consistency between the results. In addition, three genes exhibited significant differences in expression in different time with the spraying urea and overall trend was an initial increase 2 days after the treatment followed by a decrease over the duration of drought stress. Results showed that an increase expression in the key genes(BADH, CMO and PEAMT) of glycinebetaine synthase in maize leaves under drought stress was induced by spraying urea, induction effect of urea + catechol was more significant. The relative expression of CMO and PEAMT gene increased by a large increase.4. Grey correlation analysis showed that there was extremely significant positive correlation between choline and glycineglycinebetaine contents, BADH activities and glycineglycinebetaine synthesis key gene expression, and it were also significant positive correlation between PEAMT and CMO activity in maize leaves after foliar water under drought stress. There were also extremely significant positive correlation between choline content and PEAMT activity, CMO, PEAMT gene expression after foliar urea+catechol(DS+U+C) application. Results showed that synthesis and accumulation of glycinebetaine was closely related with precursor substrate choline content, PEAMT activity, CMO activity, BADH activity and gene relative expression amount after urea application alone or urea + catechol(DS+U+C) under drought stress.5. The nitric oxide(NO) content of each treatment were hight at the 2 days, and decreased significantly during the rest with the time exposure to drought stress. The NO content was significantly greater in Urea + Catechol + Sodium nitroprusside(U+C+SNP) as compared to that in the other treatments. This result indicated that foliar applied urea resulted in a significant effect on the NO content in maize leaves under drought stress. SNP has promoted effect for the induction of urea, and the effect of L-NAME was obvious inhibition.This study confirmed that exogenous application of urea improved maize tolerance to drought; by signaling to stimulate NO burst to induce increased tolerance to drought. Therefore, it activated downstream expression of key enzymes involved in glycinebetaine biosynthesis, including PEAMT, CMO and BADH. Furthermore, application of urea improved PEAMT, CMO and BADH activities and increased the choline content in the maize leaves, resulted in an increased accumulation of glycine glycinebetaine leading to an increased tolerance to drought stress.