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 .