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Abbreviations: B -blue light; Ci -intercellular CO2 concentration; DI0/RC -dissipated energy flux per reaction center; E -transpiration rate; ET0/RC -electron transport flux from QA to QB; Fm -the maximum fluorescence in the OJIP curve; Fo -the minimum fluorescence in the OJIP curve; gs -stomatal conductance; M0 -the initial slope from 0.02 ms to 300 ms in a linear time scale; OEC -oxygenevolving complex; PItotal -performance index for the conservation of energy from photons absorbed by the PSII antenna to the reduction of PSI acceptors; PN -net photosynthetic rate; PQ -plastoquinone; QA -primary quinone acceptor of PSII; QA --reduced primary quinone acceptor of PSII; QA + -oxidized primary quinone acceptor of PSII; QB -secondary quinone acceptor of PSII; R -red light; RC -reaction center; RC/CSm -reaction centers per CS (t = m); VI -normalized variable fluorescence at 30 ms (I point); VJ -normalized variable fluorescence at 2 ms (J point); VPD -vapor pressure deficit; Vt -normalized variable fluorescence at time t; WUE -wateruse efficiency; δRo -efficiency with which an electron from QB is transferred until PSI acceptors; φEo -quantum yield of the electron transport flux from QA to QB; φPo -maximum quantum yield of primary photochemistry; φRo -quantum yield of the electron transport flux until the PSI electron acceptors; ψEo -electron transport efficiency from QAto the PSI electron end acceptors; ψRo -electron transport efficiency except QA.

The dried stigmas of Crocus sativus, commonly known as saffron, are consumed largely worldwide because it is highly valuable in foods and has biological activities beneficial for health. Saffron has important economic and medicinal value, and thus, its planting area and global production are increasing. Petals, which are a by-product of the stigmas, have not been fully utilized at present. We compared the metabolites between the stigmas and petals of C. sativus using a non-targeted metabolomics method. In total, over 800 metabolites were detected and categorized into 35 classes, including alkaloids, flavonoids, amino acids and derivatives, phenols and phenol esters, phenylpropanoids, fatty acyls, steroids and steroid derivatives, vitamins, and other metabolites. The metabolite composition in the petals and stigmas was basically similar. The results of the study showed that the petals contained flavonoids, alkaloids, coumarins, and other medicinal components, as well as amino acids, carbohydrates, vitamins, and other nutritional components. A principal components analysis (PCA) and an orthogonal partial least-squares discriminant analysis (OPLS-DA) were performed to screen the different metabolic components. A total of 339 differential metabolites were identified, with 55 metabolites up-regulated and 284 down-regulated. The up-regulated metabolites, including rutin, delphinidin-3-O-glucoside, isoquercitrin, syringaresinol-di-O-glucoside, dihydrorobinetin, quercetin, and gallocatechin, were detected in the petals. The down-regulated metabolites were mainly glucofrangulin B, acetovanillone, daidzein, guaiazulene, hypaphorine, indolin-2-one, and pseudouridine. KEGG annotation and enrichment analyses of the differential metabolites revealed that flavonoid biosynthesis, amino acids biosynthesis, and arginine and proline metabolism were the main differentially regulated pathways. In conclusion, the petals of C. sativus are valuable for medicine and foods and have potential utility in multiple areas such as the natural spice, cosmetic, health drink, and natural health product industries.

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