1021-4437/05/5205- © 2005
Russian Journal of Plant Physiology, Vol. 52, No. 5, 2005, pp. 623–628. Translated from Fiziologiya Rastenii, Vol. 52, No. 5, 2005, pp. 701–707.
Original Russian Text Copyright © 2005 by Aksenova, Konstantinova, Lozhnikova, Golyanovskaya, Gukasyan, Gatz, Romanov.
Day length and phytohormones affect considerably
potato tuberization [1, 2]. However, biochemical mech-
anisms underlying these effects are obscure until now.
Potato wild species and subspecies can produce tubers
only under conditions of short day (SD) (long night, to
be correct), i.e., they are characterized by a strict SD
response of tuberization. Many
cultivars manifest a weaker SD response of tuberiza-
tion. Since the magnitude of the photoperiodic response
affects the time and synchronicity of potato yield pro-
duction in the regions at various latitudes, the investiga-
tion of tuberization photoperiodic control is of impor-
tance not only for basic but also for applied aspects of
Phytochrome is a principal photoreceptor of the day
length. At present, several (more than ﬁve) phyto-
chrome forms are known with apoproteins encoded by
different genes . Phytochrome A and B are most
studied; their genes occur in potato plants as well [4, 5].
In experiments with transgenic potato plants of
subspecies  and cultivated cv. Désirée , it
was shown that phytochrome B is an important compo-
nent of the photoperiodic control of tuberization
involved in the inhibition of tuber initiation by LD.
One of the ways for LD action on potato tuberiza-
tion is the control of phytohormone content by a photo-
period . All main phytohormones, GAs and cytoki-
nins primarily, affect substantially tuber formation .
Some researchers reported that the molecular mecha-
nisms of phytochrome B action are tightly related to
both GA  and cytokinin  activities. Gibberellins,
which accumulate under LD regime, are known as
potent inhibitors of tuberization . However, recent
experimental data indicate a more complex pattern of
GA action on tuber initiation, which is yet poorly stud-
ied. Thus, potato transformants of
expressing the anti-
gene and produc-
ing tubers under LD, manifested phenotypic features
characteristic of GA-enriched plants (stem elongation,
pale green color, and others). They expressed actively
Photoperiodic and Hormonal Control of Tuberization
in Potato Plants Transformed with the
N. P. Aksenova*, T. N. Konstantinova*, V. N. Lozhnikova*,
S. A. Golyanovskaya*, I. A. Gukasyan*, C. Gatz**, and G. A. Romanov*
*Timiryazev Institute of Plant Physiology, Russian Academy of Sciences,
Botanicheskaya ul. 35, Moscow, 127276 Russia;
fax: 7 (095) 977-8018; e-mail: firstname.lastname@example.org
**Institute of Plant Science at the Goettingen University,
D-37073 Goettingen, Germany
Received February 17, 2005
—We studied photoperiodic and hormonal regulation of tuberization in wild-type potato (
L., cv, Désirée) plants and derivative transgenic plants harboring the
which encodes the phytochrome B apoprotein, under the control of the cauliﬂower mosaic virus 35S promoter.
Plants were cultured on hormone-free Murashige and Skoog nutrient medium containing 5% sucrose or on the
same medium supplemented with 1 mg/l kinetin under conditions of long day (LD, 16 h), short day (SD, 10 h),
or SD with interrupted long night. We estimated cytokinins (zeatin and zeatin riboside) in underground and
aboveground plant organs by the ELISA technique and GA activity in a bioassay with dwarf pea seedlings.
Under LD conditions, transgenic plants produced substantially less tubers than wild-type plants. Kinetin addi-
tion to the culturing medium resulted in stimulation of tuberization under LD conditions, especially pronounced
plants. The content of cytokinins and the activity of GA were much higher under LD conditions,
especially in leaves. The total level of both phytohormones was higher in transformed as compared to wild-type
plants. A relation of phytochrome-dependent tuberization to the hormonal status of underground and above-
ground plant organs and possible reasons for kinetin stimulatory effect on this process are discussed.
Key words: Solanum tuberosum - tuberization - photoperiodism - phytochrome - GA - cytokinins - source–sink
—control wild-type plants; DI—darkness
interruption; LD—long day; MS—Murashige and Skoog nutrient
medium; SD—short day.