| Maize is one of the most important food crops in our country. Maize acreage in Jilin Province ranks the first in our country, and it is the bases of our country’s major grain production. It plays an important mission to ensure national food security. Environmental changes can lead to epigenetic changes, and these changes can be inherited. Morphology in maize are different in different cultivation measures. In extreme density gradient magnitude and fertilizer, the response performance of maize is different, so whether epigenetic has changed in the molecular level, what changes have occurred, especially in some apparent changes in regulation, yet unclear. In this paper, in different planting densities and fertilizer gradient magnitude, the impact of maize growth in different cultivation measures was researched, including the hybrids and parental DNA methylation level and the relationship between maize growth in different cultivation and DNA methylation variation. We tried to find some regulation of DNA methylation in epigenetic traits expression by environmental factors. In order to, the research can provide new ways and means for the theoretical research in maize breeding and cultivation. The results were as followed:(1) The application of nitrogen and phosphorus fertilizer was benefit to the growth in maize. In certain range, the height, stem diameter, leaf area, leaf area index and chlorophyll content of maize were increased by fertilizer application. With increasing amount of nitrogen, plant height, stem diameter increases, corn leaf area, leaf area index, chlorophyll content and net photosynthetic rate increased first and then decreased. The plant height and stem diameter were increased with the increasing amount of phosphorus, and also increase leaf area and leaf area index in jointing stage and big trumpet period. After silking, the chlorophyll content in maize was increased with the increasing phosphorus fertilizer application rates. It was no obvious impact on net photosynthetic rate with phosphorus fertilizer. Nitrogen and phophorus fertilizer increased maize yield. It was increased with the increasing amount of fertilizer, when it exceeds the critical value, yield was lower. The highest yield was11944.7kg/hm2when the nitrogen rate was224kg in nitrogen experiment. The highest yield was12001.7kg/hm2, when the phosphorus rate was95.8kg in phosphorus experiment. Maize yield was positively correlated with grain number and grain weight, but it was no obvious impact with volume-weight. In suitable planting density, the increasing yeild mainly depended on the increasing number of grains and kernel weight. (2) It was increased in plant height, stem diameter reduced, leaf area, chlorophyll content and net photosynthetic rate with increasing density. Corn leaf area index with increasing population density was increased, but with increasing planting density, the speed of leaf area index increasing was slow down. Maize yield was increased with density, when the density exceeds a certain range, the yield decreased. The maximum yield was11428.9kg/hm" when the density was62,000/hm2. In a certain extent, heavy planting density will reduce the kernel weight, volume-weight and grain number.(3) This research used MSAP technique to analyse methylation levels in maize hybrids and parental in different cultivation measures. The results showed that:compare to the parental, the overall methylation level in hybridization was lower. The methylation levels of paternal Jid850CHG sites decreased with nitrogen applicaton, while the level of CG sites methylation was contrast, slightly increased. The CHG methylation level in hybrids was increased with increasing N fertilizer, CHG hypermethylation variability in maternal Ji1037was increased with amount of nitrogen. CG hypermethylation level variation correlated with amount of nitrogen in hybrids. With the increasing amount of nitrogen, the more likely CG hypermethylation variation appeared. Demethylation sites CG hypomethylation mainly dominated, especially in hybrids. The variation between CG and CHG hypomethylation in male was not obvious, but they are negatively correlated with the amount of nitrogen fertilizer. In parentage, CG hypomethylation variation was decreased with increasing nitrogen rate. There was no obvious difference in CHG hypomethylation among all the treatments. CG demethylation variability in hybrids was significantly increased with nitrogen amount, which is the opposite result with parent indicated that genomic stability in hybrids by methylation affects gene expression patterns may be different from both parents.(4) The CG methylation level in paternal was negatively correlated with the application of phosphorus, while it was positive correlation in female and no correlation in hybrids. CG hypermethylation in hybrids was positively correlated with the increasing amount of phosphorus. CG hypomethylation variation dominated mainly in male, and CG demethylation variation was positively correlated with phosphorus rates. CG and CHG hypomethylation was positively correlated with phosphorus rates in hybrids. The same trends in hypomethylation variation with increasing phosphorus rates between hybrids and male parent indicated that this CG hypomethylation response patterns inherited from the male parent.(5) In the paternal, CHG sites methylation levels was increased with increasing density, showing a positive correlation relationship. CG and CHG methylation level in maternal and hybrids were no obvious difference. The CHG hypermethylation variation was increased in male with increasing density. The variation of CG and CHG methylation pattern in hybrids and parents are basically the same, it indicated that the variation of CG and CHG methylation pattern was no relationship with genotype, and treatment D3(60000/hm2) is the turning point of density gradient affecting DNA methylation.(6) In different nitrogen rates, the major agronomic and physiological were significant positively correlated with CHG methylation level and CG hypomethylation. It was indicated that changes in the relationship was determined by the same factor (N application rates), and make a similar reaction. However, since the nuclear genome stability and transcriptional activity were impacted by CHG methylation, so that the changes in the phenotypic adaptation displayed processing stage of nitrogen, at least, it was controled in partly by the CHG methylation signal. The relationship between phosphorus and DNA methylation were only appeared on certain characters throughout the growth period of performance, but most characters were apperared by nitrogen level and methylation, indicating that the changes of methylation pattern in nitrogen was more sensitive than that’s in phosphorus conditions. There was no correlation between characters and methylation in different densities throughout the growth period, only in a certain period of related. This showed that the critical point was not reached by environment change to the methylation, so the correlated with methylation levels was not obvious, or it had no effect on the density.(7) Changes in the environmental conditions of cultivation, some of cytosine methylation were changed in plant genomes. First, the response genes were controlled by methylation, which is methylation modification that was directed controlling gene expression. Another possibility is that methylation changes in some non-gene effected chromatin structure in genome stability and indirectly affected gene expression. This study showed variation of pattern in maize parents and hybrids methylation level in different cultivation conditions. Some results showed different on the characters between hybrids and parent, that indicated DNA methylation patterns in hybrids had great changes and adjustment to coordinate cooperative heterogeneous gene expression from the parents, and make efficient transcription of certain genes, and inhibited gene transcription, these expression of genes may be related to the formation of heterosis. |
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