1021-4437/01/4804- $25.00 © 2001
Russian Journal of Plant Physiology, Vol. 48, No. 4, 2001, pp. 415–420. Translated from Fiziologiya Rastenii, Vol. 48, No. 4, 2001, pp. 485–490.
Original Russian Text Copyright © 2001 by Drozdova, Bondar, Bukhov, Kotov, Kotova, Maevskaya, Mokronosov.
Light quality is known to regulate plant processes
[1–5]. Among photoregulatory responses, the morpho-
genetic responses are of particular interest . The
most contrasting responses to long-term illumination
were obtained with blue and red light. BL was found to
activate the development of the underground storage
organs in radish  and in
grown potato plants,
whereas RL stimulated the development of the above-
ground sink organs of plants (stem and petioles) .
However, we found no other detailed systematic studies
of the effects of light quality on the source–sink rela-
tions in the course of plant development.
Many authors have shown that, in addition to light
quality, plant morphogenesis is also affected by the
phytohormone content. For example, cytokinins are
often thought to stimulate the formation of tubers [8, 9].
BL was found to stimulate the formation of tubers and
the accumulation of cytokinins in the underground
cultured potato plants, whereas RL did
not affect these two processes . However, RL is
known to stimulate the accumulation of gibberellins,
phytohormones that arise in the aboveground parts of
plants, as well as stimulate growth . Thus, it seems
likely that, in plant species that form an underground
storage organ, the morphogenetic responses to light
quality result from the speciﬁc effects of BL and RL on
the synthesis of various phytohormones in different
parts of the plant.
In addition to photoregulatory responses, the devel-
opment of plant organs is controlled by metabolites.
Indeed, the effective and long-lasting source–sink rela-
tions between leaves and a developing storage organ is
a prerequisite for the development of the storage organ.
Such relations include the formation of photosynthates
in leaves, their conversion into transported metabolites,
and the active export of these metabolites. Thus, the
ability of plants grown under light of different spectral
quality to form a storage organ might be affected by the
photosynthetic activity of leaves in BL and RL .
A brief review of the literature data does not reveal
any mechanisms that determine speciﬁc photomorpho-
Effects of Light Spectral Quality on Morphogenesis
and Source–Sink Relations in Radish Plants
I. S. Drozdova, V. V. Bondar, N. G. Bukhov, A. A. Kotov,
L. M. Kotova, S. N. Maevskaya, and A. T. Mokronosov
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
Received April 10, 2000
—The accumulation of dry matter and the content of major phytohormones in the aboveground and
underground plant parts, as well as light curves and the diurnal course of photosynthesis in the leaves were stud-
ied in radish (
L.) plants of different ages that were grown under red (RL) or blue (BL) light.
As seen from the rapid increase in plant biomass, the development of storage organs (hypocotyl or tap root)
started on the 14th day after the emergence of seedling of the BL plants and on the 21st day for the RL plants.
Conversely, RL stimulated biomass accumulation in the aboveground parts (petioles and stems) already in the
early stages of plant development. Light spectral quality only slightly affected the activity and the diurnal
course of photosynthesis. The GA content was ten times higher in the aboveground parts of the RL plants than
those of the BL plants. The hypocotyl of the BL plants contained much higher amounts of cytokinins and IAA
than that of the RL plants. The speciﬁc responses of the source–sink relations to the light quality were related
to the distribution of various phytohormones between the aboveground and underground parts of the plants: RL
increased the content of gibberellins (GA) in the aboveground parts of plants, thus increasing their sink activity,
whereas BL stimulated the synthesis of cytokinins and IAA in the hypocotyl and enhanced its development.
Light quality-speciﬁc morphogenetic responses were reversed when plants were treated with exogenous GA or
paclobutrazol, an inhibitor of GA synthesis. The treatment of the BL plants with exogenous GA stimulated pet-
iole and hypocotyl elongation and induced stem formation. The treatment of the BL plants with paclobutrazol
led to shortened petioles, the ﬂattening of the storage organ, and the disappearance of the stem.
Key words: Raphanus sativus - source–sink relations - morphogenesis - phytohormones
: RL—red light, BL—blue light.