Jasminum spp. is cultivated for their fragrant flowers used in essential oil production and cosmetic uses. An attempt was made to study the temporal variations in floral scent volatiles composition including emitted, free endogenous and glycosyl‐linked volatile compounds from two summer‐blooming species namely, Jasminum auriculatum and Jasminum grandiflorum as well as from two winter‐blooming species namely, Jasminum multiflorum and Jasminum malabaricum. The overall emitted volatile organic compounds (VOCs) were found to be highest when the matrix Porapak Q 80/100 was used with dichloromethane (DCM) as elution solvent. The floral volatile emission from bud to senescence exhibited nocturnal maxima pattern for both the summer‐blooming species. Both the winter‐blooming species emitted its highest concentration at noon. The free endogenous concentrations of all VOCs were low when corresponding emitted concentrations were high. Enzymatic treatment of petal extract revealed that several aromatic volatiles including aromatic alcohols and monoterpenols are synthesized and stored in the flowers as water‐soluble glycosides; these compounds were shown to accumulate in higher amounts in flowers at late bud stage. These findings indicate the utilization of the precursors, i.e. the volatile‐conjugates, through hydrolysis followed by their release as free‐volatiles at flower opening stage. The outcome as a whole suggests a linkage among the temporal pattern of emitted volatiles, free‐endogenous volatiles and glycoside‐bound volatile compounds in all above studied Jasminum spp. and provided an overview of their floral volatilome.
Benzenoid and terpenoid volatiles are the major compounds contributing to the unique floral scent of Jasminum auriculatum. Biosynthesis and emission of specialized scent metabolites showed maturation stage specific pattern; maximum scent emission was observed when flowers start unfurling and become fully opened under in situ condition. The activities of volatile biosynthesizing enzymes and expressions of several scent-related genes correlated well with the fragrance emission patterns. We also assessed the impact of varying air temperatures (20°C, 25°C, 30°C and 35°C) on the metabolism as well as vaporization of scent volatiles. The contents of both emitted and endogenous volatiles were higher at either 25°C or 30°C and showed relatively lower amounts at both border-range temperatures (20°C and 35°C). Further, the activities of key pathway enzymes and expressions of several scent-related genes under varying temperatures exhibited similar trends with the scent emission patterns. Analysis of non-volatile metabolite contents from flowers grown under different air temperatures suggests a perturbation occurring in the primary metabolism and immediate precursors of scent compounds. The knowledge base created through these studies shall be helpful in improving the yield of floral scent production from such horticulturally important plants in controlled cultivation systems.
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