3.2.1 Alterations in scent volatile contents due to different air temperature conditions
Air temperature is a major environmental factor known to influence the biosynthesis and emission of floral scent volatiles. The contents of dominant scent compounds comprising mainly of benzenoid and terpenoid volatiles were monitored with respect to both emitted and endogenous volatiles to understand the influence of temperature on the metabolism accumulation as well as vaporization. Headspace floral volatile collection was done in the evening when the contents of emitted volatiles were in their peaks; GC-MS analysis indicated that the emission of scent compounds first increased then decreased with rise in air temperature (Figure 4, S1 ). Highest emission of benzyl alcohol, benzyl acetate, and cis -jasmone were observed at 25°C followed by 30°C. However, 2-phenylethanol and phenethyl acetate showed higher emission at 30°C. Emission of indole and other terpene volatiles were highest at 30°C followed by 25°C. Much lower emission of these major floral volatiles was observed both at 20°C and 35°C, the two border-range air temperature set out for the experiments.
The internal pools of floral volatiles were also monitored in terms of free endogenous and glycosylated volatiles to understand the influence of air temperature on the metabolism and storage of scent compounds. While free endogenous volatiles were sampled from flowers after collection of emitted volatiles, we utilized mature buds for sampling of glycosylated volatiles. This is because of the fact that mature buds were reported to contain maximum amount of glycosylated volatiles (Barman and Mitra, 2019). All the major emitted volatile compounds detected from headspace collection were also present as free endogenous volatiles. Further, it was observed that the accumulation of free endogenous volatiles in floral tissues was significantly higher at both 25°C and 30°C (Figure 5a ). However, the contents were much lower at 20°C and 35°C as was observed in the emission profile. In order to understand the influence of air temperature on the biosynthesis and storage of volatile compounds, we measured the contents of these glycosyl-bound volatiles after removing the bound glycosyl moiety by enzymatic hydrolysis. It was observed that levels of accumulation of aromatic alcohols and monoterpenol volatiles increased with rise in air temperature (up to 30°C) and then followed a sharp decline upon reaching the highest set air temperature (35°C) for this study (Figure 5b ).
3.2.2 Activities ofmajor pathway enzymes of volatile biosynthesis under the influence of temperature
In order to understand the role of temperature on the metabolism of volatile compounds, the activities of a few key enzymes of scent volatiles biosynthesis was studied. Based on the earlier information about the floral stages showing higher activities of particular enzymes under in situ conditions, the crude protein extracts were prepared from floral tissues either at late bud stage or flower blooming stage. The (petal) tissues were collected from different J. auriculatum plants grown at different temperature inside the plant growth chamber. Higher in vitro activities of PAL, β-glucosidase and BEAT were found in J. auriculatumflowers when grown at 25°C, followed by 30°C (Figure 6a-c) . High activities of PAR and MTS were recorded both at 25°C and 30°C temperature regime (Figure 6d, e ). Lower activities of all the above enzymes were detected at 20°C and 35°C, the two border range air temperatures set out for conducting these experiments inside growth chamber. Chromatograms indicating product formation by BEAT, PAR and MTS are presented in Figure 6f, g, h .