Levels of ethylene and polyamines (PAs) were
measured during organogenesis of hypocotyl explants of
two species of passion fruit (Passiflora cincinnata Masters
and Passiflora edulis Sims f. flavicarpa Degener ‘FB-100’)
to better understand the relationships of these regulators
and their influence on cell differentiation and morphogenesis.
Moreover, histological investigation of shoot ontogenesis
was conducted to characterize the different events
involved in cell redifferentiation and regulation of PA and
ethylene levels. A delay was observed in morphogenic
responses of P. edulis f. flavicarpa as compared to
P. cincinnata, and these changes coincided with production
of elevated levels of polyamine and ethylene levels. During
differentiation, cells showed high rates of expansion and
elongation, and high ethylene levels were associated with
high PA levels, suggesting that the two biosynthesis pathways
were highly regulated. Moreover, their interaction
might be an important factor for determining cell differentiation.
The addition of PAs to the culture medium did
not promote organogenesis; however, the incorporation of
the PA inhibitor methylglyoxal bisguanylhydrazone in the
culture medium reduced shoot bud differentiation, suggesting
the need to maintaining a minimum level of PAs
for morphogenic events to take place.