Study On Early Response Of Maize Root Tips To Osmotic Stress

Osmotic stress can cause the growth restriction and yield reduction of many crops,including maize.Improving the tolerance of maize to osmotic stress caused by water shortage and other factors is an effective way to improve the survival of crops in osmotic stress environment.Roots are organs that are in direct contact with soil and are the first to perceive soil water deficit.The root system is an important organ for soil water absorption.However,the root absorption mainly takes place at the root tip,which is involved in the initial response to osmotic stress.The early response of maize root tips to osmotic stress is seldom reported at the proteomic level.At present,most of the studies on proteins in response to osmotic stress focus on medium and long term,few of which are less than 1 h.In this study,we compared the early physiological and proteomic analysis of osmotic stress on root tips of maize hybrid zhengdan 958 at seedling stage.Polyethylene glycol(PEG)6000 was used to treat maize root tips for 0.5 h,and 1 cm samples from the root tips of maize were selected as the control.The main research results of this paper are as follows:(1)Osmotic stress(0.5 h after PEG treatment)leads to increased accumulation of reactive oxygen species(ROS),resulting in membrane lipid peroxidation,and the accumulation of osmotic substances,and the activity of antioxidant enzymes enhanced.After 0.5 h osmotic stress,the content of malondialdehyde(MDA)in maize root tips was significantly higher than the control.Proline content increased significantly;The content of soluble sugar hardly changed compared with the control.The activities of superoxide dismutase and catalase were significantly increased.The results showed that the physiological mechanism of maize root tips response to osmotic stress was through the synergistic action of antioxidant enzymes such as superoxide dismutase and catalase to eliminate harmful free radicals and alleviate oxidative stress.(2)Proteomic analysis of early stage of maize root tips under osmotic stress Two dimensional gel electrophoresis(2-DE)was used to isolate the proteome expressed in maize root tips.The proteome changes before and after root tips stress were analyzed by tandem mass spectrometry(LC-MS/MS).20 proteins with varying abundances(≥2 times,p-value ≤ 0.05)were identified.The abundance of 12 protein spots was increased compared with the control,and the abundance of 8 protein spots was decreased.These differential proteins are involved in a variety of intracellular processes,including energy and carbohydrate metabolism,antioxidant and defense,protein biosynthesis,cell structure,molecular chaperones and other biological processes,indicating that these pathways are susceptible to early osmotic stress.After the early osmotic stress,metabolism is related(enolase/ATP synthase/H(+)transport ATPase),antioxidant(superoxide dismutase/NAD(P)H dehydrogenase quinone)and proteins related to cytoskeleton(tubulin)abundance was enhanced compared to the control.These results indicate that the early adaptability of maize root tips to osmotic stress is closely related to antioxidant,cell structure and metabolic pathways.(3)The expression patterns of 18 differentially expressed genes under early osmotic stress were studied by real-time PCR.The results showed that the change of transcription level was consistent with that of protein level at the early stage of osmotic stress.The above results will provide new clues for the early response mechanism of maize root tips to osmotic stress,and provide new ideas for the regulation of early osmotic stress in crops,and help to develop new drought resistance breeding methods.