# The Significance of Calcium in Photosynthesis
###### Abstract  
As a secondary messenger, calcium participates in various physiological and biochemical reactions in plants. Photosynthesis is the most extensive biosynthesis process on Earth. To date, researchers have found that some chloroplast proteins have Ca\({}^{2+}\)-binding sites, and the structure and function of some of these proteins have been discussed in detail. Although the roles of Ca\({}^{2+}\) signal transduction related to photosynthesis have been discussed, the relationship between calcium and photosynthesis is seldom systematically summarized. In this review, we provide an overview of current knowledge of calcium's role in photosynthesis.  
calcium; chloroplasts; photosynthesis; calmodulin; energy dissipation 21 January 20192018 March 201921 January 20192018 March  
Photosynthesis is highly sensitive to environmental stress, and inappropriate environments will cause a decrease in photosynthesis. Stomatal and non-stomatal limitations are the two causes of inhibition of photosynthesis [11]. In this review, we attempt to elucidate the mechanisms of Ca\({}^{2+}\)-related pathways involved in photosynthesis (Figure 1). The photosynthesis-correlated proteins regulated by calcium are given in Table 1.  
Figure 1: Photosynthesis-related pathways regulated by Ca\({}^{2+}\). (**A**) Under light conditions, the proteins shown in this figure are all regulated by Ca\({}^{2+}\), in which CAS is related to stomatal movement, photosynthetic electron flow, and CCM. PS1 subunits include PsaN, PsaA, PsaL, and PsaD. FD can interact with PS1 subunits to participate in electron transfer. PS2 is composed of OEC and D1 protein. OEC subunits include PsbO, PsbP, PsbQ, etc. OEC is involved in photosynthetic water oxidation. D1 protein, PsbS, and VDE are involved in energy dissipation. CPN10, Tic32, Tic110, ACA1, (p)ppGpp, and AFGLL1 play different roles in chloroplasts. (**B**) SBPage, TKL, and FBPase are the key enzymes related to Ca\({}^{2+}\) in the Calvin cycle. (**C**) Stomatal movement is regulated by Ca\({}^{2+}\). (**D**) Ca\({}^{2+}\) is involved in chloroplast movement. Abbreviations: ACA1, _Arabidopsis thaliana_ Ca\({}^{2+}\)-ATPase; AFG1L1, ATPase family gene 1-like protein 1; APX, ascorbate peroxidase; CaM, calmodulin; CAS, Ca\({}^{2+}\) sensor; CAT, catalase; CCM, CO\({}_{2}\) concentration mechanism; Ch-CPN10, 10 kDa chloroplast co-chaperonin; CP12, 12 kDa chloroplast protein; FBPase, fructose-l,6-bisphosphatase; FD, ferredoxin; IP\({}_{3}\), the inositol 1,4,5-trisphosphate OEC, oxygen-evolving complex; PA, phosphatidic acid; PI3P, phosphatidylinositol 3-phosphate; PLD, phospholipase D; PLC, phospholipase C; (p)ppGpp, Guanosine 5’ triphosphate (or 5’-diphosphate) 3’-diphosphate; PS1, photosystem 1; PS2, photosystem 2; ROS, reactive oxygen species; SAMTL, s-adenosylmethionine transporter-like; SBPase, sedoheptulose-1,7-bisphosphatase; SOD, superoxide dismutase; STN8, Thylakoid-associated kinases; Tic110, the subunit of chloroplast inner envelope protein complex; Tic32, the subunit of chloroplast inner envelope protein complex; TKL, Transketolase; Toc, chloroplast outer envelope protein complexes; VDE, violaxanthin de-epoxidase.