| Extreme temperature is one of the disastrous factors which seriously affect plant growth and development among abiotic stresses.Extreme temperature enhances the lipid peroxidation of membrane,influences chlorophyll(Chl)biosynthesis,inhibits photosynthesis,and leads to the accumulation of reactive oxygen species(ROS)and the reduction of crop yield and quality.Under temperature stress,higher plants could regulate different biological processes and trigger the defense mechanism to scavenge ROS and maintain the redox balance.Celery(Apium graveolens L.)is a biennial herb and one of the most impotant vegetables in the family of Apiaceae in China and the world.Temperature is one of the most important factors for celery growth and development.To characterize the molecular mechanisms in response to extreme temperature in celery plants and analyze the influence of extreme temperature on transcriptional regulation of genes related to Chl and ascorbic acid(AsA),we identified the proteins involved in Chl biosynthesis by the proteomic approach,analyzed the Chl and AsA contents in celery leaves,and then studied mRNA levels of genes related to Chl and AsA metabolic pathways.The main results were as follows:1.The celery leaves were harvested from ’Ventura’ exposed to different temperature stresses(4 ℃,25 ℃ and 38 ℃)after 24 h,prepared for the experimental material.The contents of Chl a and Chl b were calculated using the equations of Lichtenthaler.The expression patterns of genes related to Chl biosynthesis and degradation were analyzed in celery leaves by quantitative real-time PCR(qRT-PCR).The Chl contents were significantly reduced under both heat and cold treatments in celery leaves.The expression levels of 15 genes involved in Chl biosynthesis were also reduced.Furthermore,inhibition of Chl biosynthesis was higher under heat stress than under cold stress,which was similar to the trend of expression of AggltX,AgHEMA,AgHEMB,AgCHLH,AgCRD,and AgHEME.The mRNA levels of magnesium chelatase(Mg-chelatase)and glutamate-1-semialdehyde aminotransferase(GSAT)identified by the proteomic approach were not related to its protein levels.The analysis results by the proteomic approach suggested that high temperature inhibited photosynthesis in celery leaves,while glycolysis,amino acid metabolism,protein metabolism,and detoxification were enhanced under cold stress.The proteins constructed the temperature-stress response network in celery leaves.2.The leaf blades and petioles of ’Ventura’ and ’Liuhehuangxinqin’ at three different stages(35,50,and 65 days after sowing)were prepared for experiments.Total of 19 genes related to AsA biosynthesis,recycling,and degradation were selected.AsA levels and the expression levels of related genes were analyzed in order to study the effect of stages,varieties,and tissues on AsA contents in celery.AsA levels were higher in ’Ventura’,which were similar to the expression trends of AgGalDH,AgGalLDH,and AgGR.Results suggested that the D-mannose/L-galactose pathway was the vital biosynthetic pathway in celery leaves.In ’Liuhehuangxinqin’,the D-galacturonic acid pathway contributed to AsA accumulation in petioles more than in leaf blades.AsA levels changed with tissues,growth stages,and varieties in celery plants.3.The AsA levels of celery leaves under temperature stresses were determined by the method as described by Kampfenkel et al.The expression profiles of 26 genes involved in AsA biosynthesis,recycling,and degradation were analyzed by qRT-PCR in ’Ventura’leaves.AsA levels were decreased under temperature stress.As the major pathway in AsA biosynthesis in celery plants,most genes related to the D-Man/L-Gal pathway were affected by extreme temperature.AgGalDH and AgGalLDH were involved in the last steps in AsA biosynthesis,and the expression levels of AgGalDH and AgGalLDH were reduced under temperature stress.The expression level of AgGalUR was dramatically increased,showing the D-galacturonic acid pathway may be enhanced by extreme temperature.The expression trends of the AgAPXs genes were different under heat or cold stress.The results showed that AsA levels were regulated by a complex regulatory network under temperature stress in celery leaves.Those results demonstrated that celery could resist the environment stress by regulating the biological processes.Extreme temperature led to the reduction of Chl contents and AsA levels in celery leaves.The expression profiles of the genes related to Ch1 and AsA biosynthesis and degradation played an important role in the accumulation of Chl and AsA.The results offered a systematic analysis about the molecular mechanism in response to temperature stress in celery plants and maybe contributed to breeding celery varieties resistant to extreme temperature. |
