Physiological And Proteomic Studies On Coleoptile Growth Of Maize(Zea Mays L.)

Coleoptile is a model organ for studying cell elongation.The coleoptile is a unique structure in monocot crops,such as maize,wheat and rice.It protects and leads the upward growth of the enclosed primary leaves during seed germination in the soil,which is a key step for the successful seedling establishment.Moreover,the coleoptile contains a small quantity of chloroplasts,which can provide additional nutrients for the seedling through photosynthesis.In the present study,maize coleoptile was sampled at four growth stages,i.e.,initial,slow,rapid,and stable growth stage,based on the growth curve,dry mass accumulation.The sample was collected for researching the cell morphology change,hormone level change and proteomic change.The main results were as follow:(i)Under the dark conditions,maize coleoptile grows in the manner of whole elongation,i.e.,S-shaped curve.Its growth were slow from 0 h to 48 h,fast significantly from 48 h-120 h,with the maximum growth rate at 72 h,and then slow again from 120 h afterwards,with almost unchanged length(ca.5.1 cm).The dry weight accumulation of maize coleoptile was consistent with the growth curve.(ii)Microscopy showed that the coleoptile growth was due to the enlargement of cell volumes.Coleoptile cells were small and were closely arranged before 36 h,and then their lengths increased along with coleoptile growth.(iii)During the coleoptile growth,the contents of auxin and abscisic acid decreased gradually,whereas the content of zeatin increased continuously.The growth in vitro showed that maize coleoptile aged 72 h was more sensitive to auxin than other growth periods;exogenous auxin and gibberellin promoted the in vitro growth of coleoptile segments,whereas abscisic acid inhibited the in vitro growth of coleoptile segments.(iv)Using two-dimensional electrophoresis and mass spectrometry,we identified 66 differentially accumulated proteins,representing 47 different proteins.These proteins are involved in stress response,hormone response,cytoskeleton synthesis,protein synthesis,storage protein,metabolism and signal transduction.Especially,the stress-reponsive proteins,such as ascorbic acid peroxidase,glutathione transferase and adenosine methionine synthase,accumulated in large quantities during the rapid and stable growth of maize coleoptiles,which may help to remove toxic metabolites from the growth of coleoptiles and maintain the stability of coleoptile environment.In addition,rapid elongation of coleoptiles required large amount of tubulin and actin,and the senescence of coleoptile may be related to the high abundance of abscisic acid protein in the stable stage of coleoptile growth.In this study,I analyzed the characteristics of the coleoptile growth and the change of hormones and proteomes during coleoptile growth.The results in the thesis would help for understanding the regulation mechanism of maize coleoptile growth.