| Acting as an important channel for material and signal exchange between the over-ground and underground parts of the vegetable seedlings,hypocotyl is sensitive to the environmental stimuli and responds quickly according to environmental changes by adjusting hypocotyl elongation.Hypocotyl has been a model system to study the effects of environmental factors on seedling growth responses.The regulation mechanism of single environmental factor on hypocotyl elongation has been extensively studied at physiological and molecular level,but the information about synergy regulation of multi factors is still scarcely.In this study,the interaction effects of light intensity,temperature and water potential on hypocotyl elongation in cv.Cuibai 3 of Brassica rapa were analyzed.And the changes in thickness and composition of the cell wall and the protein expression profile during hypocotyl elongation were analyzed,which laid a theoretical foundation for further study on the molecular mechanism of hypocotyl elongation.The main results were as follows:1.The orthogonal experimental design with 3 factors and 2 levels was adopted to analyze the interaction effect of light intensity,temperature and water potential on hypocotyl elongation.Under the synergistic effects of the three environmental factors,the hypocotyl length and elongation rate in B.rapa were significantly different among different treatments.The longest hypocotyl and the maximum elongation rate were observed as the seedlings grew under the low light,high temperature and high-water potential.Light intensity regulated hypocotyl elongation in B.rapa significantly at rapid elongation stage,stationary elongation stage,and plateau stage,while temperature and water potential only had significant effect at the rapid elongation stage.According to the interaction analysis of the three environmental factors,the effects of light intensity × temperature and light intensity × water potential reached significant level at the rapid elongation and stationary elongation stage,respectively.The effects of light intensity × temperature × water potential reached significant level in the rapid elongation stage.2.Light intensity,temperature,and water potential regulated hypocotyl cell elongation both in isolation and in synergy.During hypocotyl elongation,the outer wall of epidermal cells changed with the trend of thickening-maintaining-thickening,while the inner wall of epidermis and the cortical cell wall changed with the trend of thickening-thinning-thickening.Further study revealed that the imbalance of wall deposition and hypocotyl elongation contributed to the dynamic changes in wall thickness.Low light promoted hypocotyl elongation by restricting the accumulation of cellulose,hemicellulose,and pectin.High temperature and high-water potential induced the increase in hypocotyl length by repressing pectin deposition,indicating pectin was the co-target of environmental factors in regulating hypocotyl elongation.3.A comprehensive isobaric tag for relative and absolute quantitation(i TRAQ)-based proteomic approach was adopted,and 7259 proteins were quantified totally,but only 378 differentially expressed proteins(DEPs)were responsive to the three environment factors.The DEPs were involved in a variety of biochemical processes,including signal transduction,cytoskeletal organization,carbohydrate metabolism,cell wall organization,protein modification,and transport,etc.The DEPs did not function in isolation but acted in a large and complex interaction network to affect hypocotyl elongation.Among the DEPs,phyB was outstanding for its significant fold change in quantity and complex interaction networks with other DEPs.In addition,changes of sensitivity to environment factors in phyB-9 suggested its key role in the regulation of hypocotyl elongation.Overall,the data presented in this study show a profile of proteins interaction network in response to light intensity,temperature and water potential and provides molecular basis of hypocotyl elongation in B.rapa. |
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