The Involvement of Cyclic ADPR in
Photoperiodic Flower Induction of
Pharbitis nil
Adriana Szmidt-Jaworska,* Krzysztof Jaworski, and Jan Kopcewicz
Department of Physiology and Molecular Biology of Plants, Institute of General and Molecular Biology, Nicolaus Copernicus
University, Gagarina St. 9, 87-100 Torun, Poland
A
BSTRACT
Cyclic adenosine diphosphate ribose (cADPR) is a
potent endogenous calcium-mobilizing agent syn-
thesized from NAD
+
by ADP-ribosyl cyclases
described for several animal cells. Pharmacological
studies suggest that cADPR is an endogenous mod-
ulator of Ca
2+
-induced Ca
2+
release channels. There
is also information about the sub-micromolar con-
centration of cADPR in plant cells. Whether cADPR
can act as a Ca
2+
-mobilizing intracellular messenger
in plant tissue is an unresolved question. Despite the
obvious importance of monitoring cADPR cellular
levels under various physiological conditions in
plants, its measurement has been technically diffi-
cult and requires specialized reagents. In the present
study a widely applicable sensitivity assay for cADPR
is described. We show that Pharbitis nil tissue from
cotyledons contains a certain cADPR level. To ex-
plain the possible roles of this second messenger in
photoperiodic flower induction, some physiological
experiments were also performed. The exogenous
applications of cADPR to Pharbitis nil plants, which
were exposed to a 12-h-long subinductive night,
significantly increased flowering response. Never-
theless 8-Br-cADPR inhibited flowering when these
compounds were applied during a 16-h-long
inductive night. The effect of ruthenium red, a cal-
cium channel blocker and ryanodine, a calcium
channel stimulator, on the photoperiodic induction
of flowering was also studied. Ruthenium red, when
applied before and during an inductive 16-h dark
period, slightly inhibited flowering, whereas ryano-
dine, when applied before and during a 12-h long
subinductive night, stimulated flower bud forma-
tion. We also confirmed evidence that Ca
2+
ions are
involved in the photoperiodic induction of flower-
ing. Thus, the obtained results may suggest the
involvement of cyclic ADPR-activated Ca
2+
mobili-
zation in the photoperiodic flower induction process
in Pharbitis nil.
Key words: Ca
2+
; cADPR; Flowering; Pharbitis nil;
Photoperiodic induction.
I
NTRODUCTION
Photoperiodism is the reaction of a plant to the
changing duration, over 24 h, and the periodic
succession of light and darkness. Photoperiodic
induction of flowering is based on the perception
Received: 16 February 2006; accepted: 31 May 2006; Online publication:
26 September 2006
*Corresponding author; e-mail: asjawors@biol.uni.torun.pl
J Plant Growth Regul (2006) 25:233–244
DOI: 10.1007/s00344-006-0015-8
233