| Maize is one of the important food crops in the world. Increasing densityappropriately is the effective measure to improve maize yield. However, it is easy tocause the maize stalk fragile, lodging and serious reduction of output when the densityreaches a certain degree. Plant growth regulators can reduce plant height, shorten thebasal internode length, increase stem diameter, enhance basal internode toughness, soas to improve the lodging resistance and ensure the yield of maize. As a major plantgrowth regulator, ethephon has played an important role in production with less studyon the mechanism.The purpose of this study was to investigate the physiological and molecularbiology mechanisms of plant height-reduce induced by ethephon in maize. UsingZhengdan958, Luyu16, Yuyu22and Denghai661, Xianyu335as materials, dividedinto different plant types and plant heights. The plant leaves were sprayed withethephon at225mg/L at early elongation stage and sprayed with water as control, inorder to study the physiological and biochemical indexes of agronomic traits. Inaddition, Zhengdan958was used for the study of molecular biology basis. With thesame treatment, young stalks of5plants were taken at0,6,12,24and48hours aftertreatment. All the results of this study were as follows:1. The field investigation showed, ethephon treatment significantly reduced plantheight, ear height, stem diameter and stem increased tension, can effectively improvethe lodging resistance of maize.2. With the growth of maize, the activity of POD, SOD, MDA content andsoluble proteins in leaves were increased gradually，it reached the top at silking stage,then began to decline. The changes of physiological indexes among varieties weredifferent. Ethephon treatment can result in the increase of the activity of SOD, PODand soluble proteins, but MDA content was decreased. Ethephon treatment can alsotimely clear the active oxygen which is produced during the normal metabolism andaging process so as to reduce the degree of cell membrane lipid peroxidation of maize.As a result, the stress resistance of maize is improved and leaf senescence isdelaying.3. MSAP technology was carried out to analyse maize genomic DNA after ethephon treatment. The results showed that there were methylation sites both in theethephon treatment and contrast, with the total methylation rate were27.8%and30.1%respectively. The diversity of methylation was not notable and the methylation statuswere all based on full methylation. Further analysis of the variation of methylationpatterns of maize DNA, compared with diploid watermelon, there are a few of adjustmentsin DNA methylation pattern.3.0%of methylation sites were hypermethylated and7.3%ofmethylation sites were demethylated. With ethephon treatment, DNA methylationchange of maize was given priority to demethylated, which may be related to plantcell regulate the expression of some genes stress defense.4. Analysis of differential gene expression in ethephon induced by SCoTmolecular marker technology. Fifty fragments of differentially expressed genes wereobtained with43single primers. The expressions of26genes were up-regulated and24genes down-regulated by ethephon induction. These genes were divided into sevencategories by functional analysis including energy and metabolism-related genes(16%), unknown functional proteins (38%), unknown genes (12%), signaltransduction-related genes (2%), transcription factor-related genes (10%),resistance-related genes (20%) and cell apoptosis genes (2%). It is concluded thatdifferential expression of genes in the stalks can be analyzed with SCoT techniqueand some fragments may be related to the stalk shortening of maize.5. cDNA-AFLP technique was used to analyze the differential gene expression.The results showed that1635fragments of expressed genes were obtained with70pairs of primers. The expressions of600genes were up-regulated (36.7%),564genesdown-regulated (34.5%) and the same expressions of471genes (28.8%of the totalbands) by ethephon induction. Through the BLASTX analysis of30different genefragments of TDFs can be divided into six categories by functional analysis, includingsignal transduction-related genes (6.7%), resistance-related genes (16.7%), energy andmetabolism-related genes (20.0%), transcription factor-related genes (10%),unknownfunctional proteins (13.3%) and unknown genes (33.3%). Ethephon influence thegrowth of maize through regulating the glutathione S-transferase, aspartic acid proteinkinase and auxin-induced protein gene expressions.6. Fluorescence quantitative on ethylene biosynthesis key genes showed, ACS ofthe relative expression was96%; ACO and the relative expression amount was17%of water control. The results suggest that exogenous ethylene affect maize otherhormones or other endogenous substances, regulate the expression of genes, so thatshorten the internodes of maize. |
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