Comparative proteomic analysis provides novel insights into chlorophyll biosynthesis in celery under temperature stress. 
Chlorophyll (Chl) is essential for light harvesting and energy transduction in photosynthesis.  A proper amount of Chl within plant cells is important to celery (Apium graveolens) yield and quality.  Temperature stress is an influential abiotic stress affecting Chl biosynthesis and plant growth.  There are limited proteomic studies regarding Chl accumulation under temperature stress in celery leaves.  Here, the proteins from celery leaves under different temperature treatments (4, 25 and 38°C) were analyzed using a proteomic approach.  There were 71 proteins identified through MALDI-TOF-TOF analysis.  The relative abundance of proteins involved in carbohydrate and energy metabolism, protein metabolism, amino acid metabolism, antioxidant and polyamine biosynthesis were enhanced under cold stress.  These temperature stress-responsive proteins may establish a new homeostasis to enhance temperature tolerance.  Magnesium chelatase (Mg-chelatase) and glutamate-1-semialdehyde aminotransferase (GSAT), related to Chl biosynthesis, showed increased abundances under cold stress.  Meanwhile, the Chl contents were decreased in heat- and cold-stressed celery leaves.  The inhibition of Chl biosynthesis may be due to the downregulated mRNA levels of 15 genes involved in Chl biosynthesis.  The study will expand our knowledge on Chl biosynthesis and the temperature tolerance mechanisms in celery leaves.