Indoleamines and calcium enhance somatic embryogenesis in Coffea canephora P ex Fr.

Melatonin (MEL) and serotonin (SER) are
important indoleamines that are involved in neural transmission
in mammalian cells. They are also known to be
present in various genera of plants. The role (s) of these
indoleamines in plants are not well known. In this study,
the effects of SER, MEL, calcium, and calcium ionophore
(A23187), a calcium channel activator, on somatic
embryogenesis in Coffea canephora have been investigated.
Adding 100 lM of either SER or MEL to � strength
Murashige and Skoog (MS) medium and 0.93 lM kinetin
(KN) has resulted in enhanced induction of somatic
embryogenesis, 85 ± 3 and 62 ± 6 embryos/callus,
respectively. In the presence of either 5 mM calcium or
100 lM calcium ionophore A23187, number of somatic
embryos/callus is also increased, with 56 ± 4 and
118 ± 10 somatic embryos/callus, respectively, compared
to 25 ± 3 embryos/callus for control. The presence of
5 mM calcium chloride along with either 100 lM SER or
100 lM MEL, respectively, have also promoted somatic
embryogenesis with induction of 105 ± 6 and 78 ± 2
somatic embryos/callus. While, addition of calcium ionophore
A23187 along with either 100 lM SER or 100 lM
MEL have produced 155 ± 12 or 135 ± 8 embryos/callus,
respectively. In contrast, addition of such indoleamine
inhibitors as 40 lM p-chlorophenylalanine (p-CPA),
20 lM fluoexitine hydrochloride (prozac), 1 mM verapamil
hydrochloride (calcium channel blocker), and 1 mM
ethylene glycol-bis (b-amino ethylether)-N, N, N0, N0-tetra
acetic acid (EGTA) (a calcium chelator) individually, has
inhibited induction of somatic embryos while reducing
levels of endogenous pools of SER, MEL and indole-3-
acetic acid (IAA) levels. Calcium imaging by laser scanning
confocal microscopy (LSCM) has revealed high
fluorescence intensity in callus treated with calcium and
calcium ionophore A23187. Immunolocalization of SER in
different tissues of C. canephora has revealed that it is
localized in vascular tissues of stems, roots, and somatic
embryos, as well as in endocarps (husks) of immature
fruits.