3.1.1 Scent volatiles variations from in situ flowers
Benzenoids and terpenoids were shown to be the major volatile compounds
emitted from J. auriculatum flowers. To understand variations in
emission patterns at different stages of floral growth and maturation
until senescence, the contents of major volatiles was evaluated from
intact in situ flowers at six defined stages starting from early
bud stage to senescence stage. The emission of benzyl alcohol,
2-phenylethanol, linalool and farnesol was highest at flower blooming
(S4) stage whereas the emission of benzyl acetate and α-farnesene was
much higher at fully bloomed (S5) stage (Figure 1 ).
3.1.2 Activities ofmajor pathway enzymes of
volatile biosynthesis at different floral maturation stages
To find out any correlation between enzyme activities and scent
volatiles synthesis and emission, we attempted to measure
the amount of active enzymes (in
terms of their in vitro activities) involved in the scent
biosynthetic pathways throughout floral lifespan. The major volatile
compounds in J. auriculatum are benzyl acetate, 2-phenylethanol
and phenylethyl acetate, derived from the phenylpropanoid pathway. PAL
is the entry point enzyme of phenylpropanoid pathway
that catalyzes the formation oftrans -cinnamic acid from L-phenylalanine. Most of the benzenoid
volatile compounds are subsequently formed from trans -cinnamic
acid via C2 side chain shortening. Higher PAL activities
were recorded at time of flower blooming (S4) stage (Figure
2a ), which showed a gradual decline with subsequent stages of petal
growth and maturation until senescence. The enzyme BEAT catalyzes the
formation of benzyl acetate from the substrate benzyl alcohol in
presence of acetyl CoA. Out of the six stages the activity of BEAT was
found to be highest at flower blooming (S4) stage (Figure 2c ).
The PAR enzyme is responsible for formation of 2-phenylethanol (2PE)
from phenylacetaldehyde. Upliftment of PAR activities was observed at
late bud stage (S3) which gradually declined after the flower blooms
(Figure 2d ). Terpenoid volatiles also contribute to the floral
scent bouquet of J. auriculatum . Linalool is the major emitted
monoterpene compound. The activity of MTS responsible for formation of
linalool was also measured; MTS showed highest peak at late bud (S3)
stage followed by a gradual decline after flower blooming (S4)
(Figure 2e ). Chromatograms indicating product formation by
BEAT, PAR and MTS are presented in Figure 2f, g, h .
Many volatile compounds in J. auriculatum are present as
glycosyl-bound form. In this species, it was observed that the release
of scent volatiles started at higher rate within first few hours of
flower opening. Little is known about the enzymes involved in the
de-glycosylation process. The β-glucosidase activity was measured at
different floral maturation stages; a higher activity observed at the
flower blooming (S4) stage (Figure 2b ), which indicated the
cleavage of glucosyl moiety for easy release of volatile compounds.