Low temperature significantly influences chloroplast development and chlorophyll (Chl) biosynthesis, so effect of coldness on Chl content and Chl fluorescence characteristics was investigated in C. bungeana (Chorispora bungeana Fisch. & C.A. Mey). The levels of transcript and protein of an enzymatic step during Chl biosynthesis in response to chilling (4°C) and freezing (-4°C) were also examined in this work. Significant reduction in total Chl content was observed, but the reduction was much less at 4°C than that at -4°C. Moreover, the maximal quantum efficiency of photosystem II (PSII) photochemistry, indicated by Fv/Fm, decreased in the first 12 h, but then started to increase and reached higher levels than the control at 24 h and 48 h at 4°C, but decreased continuously at -4°C. Whereas quantum yield of PSII (ΦPSII) showed no significant difference between the chilling-stressed and the control seedlings, at -4°C, ΦPSII was markedly reduced with the prolonged treatment. In general, there were no significant responses of photochemical quenching (qP) and non-photochemical quenching (NPQ) to cold treatment. Meanwhile, the full-length cDNA of NADPH:protochlorophyllide oxidoreductase (POR, EC 1.3.1.33) was isolated and termed CbPORB (GenBank Accession No. FJ390503). Its transcript and protein content only slightly declined at 4°C, but dramatically reduced at -4°C with the time. These results strongly suggest that CbPORB possesses certain resistant characteristics and is a major player in Chl biosynthesis process involved in plant growth and development of C. bungeana under cold environmental conditions. and Y. H. Li ... [et al.].