J. Plant Biol. (2018) 61:121-130
DOI 10.1007/s12374-018-0081-z
Roles of Sugars in Controlling Flowering Time
Lae-Hyeon Cho
†
, Richa Pasriga
†
, Jinmi Yoon, Jong-Seong Jeon* and Gynheung An*
Crop Biotech Institute and Graduate School of Biotechnology, Kyung Hee University, Yongin 17104, Korea
Received: March 12, 2018 / Accepted: March 19, 2018
© Korean Society of Plant Biologists 2018
Abstract Flowering time is influenced by environmental
factors such as photosynthesis, temperature, nutrition, and
water. The main products of photosynthesis are sugars that
are mobilized to sink tissues to support plant growth and
differentiation. They also function as signals to control
various types of metabolism and developmental processes.
One of the most important transitions in the plant life cycle
is from the vegetative to reproductive phase. During that
transition, sucrose levels rise rapidly but transiently in the
phloem and shoot apexes. For several species, the addition of
exogenous sucrose promotes flowering, possibly by acting as
a main signal. Although other sugars, including glucose, also
appear to be involved in this transition, evidence for their
roles in flowering is limited. In Arabidopsis thaliana,
trehalose-6-phosphate serves as a signal to induce flowering.
However, its roles in other plants have not been reported.
Sucrose seems to function primarily in the leaf phloem to
enhance the generation of florigens such as Flowering Locus
T (FT) while trehalose-6-phosphate functions in the shoot
apical meristem to promote the flowering signal pathway
downstream of those florigens.
Keywords: Flowering time, Photosynthesis, Soluble sugars
Introduction
Sugars provide energy and carbon skeletons required for
plant growth and development. Sugars also act as signaling
molecules to regulate various developmental phases (Eveland
and Jackson 2012; Lastdrager et al. 2014; Sheen 2014). While
low levels of sugar in the leaves can induce photosynthesis
and the circulation of carbohydrates, an abundance can
promote sink-organ activities such as carbohydrate import,
storage, and consumption; defense responses; respiration; and
starch biosynthesis (Rolland et al. 2006). Sucrose, a major
photosynthetic product, functions as a signal to control
growth and differentiation (Tognetti et al. 2013). Its hydrolytic
products glucose and fructose, as well as their downstream
metabolic intermediates trehalose and trehalose-6-phosphate,
also act as signals (Eveland and Jackson 2012; Lastdrager et
al. 2014; Sheen 2014). Here, we present an extensive review
of research on the roles of sugars, in particular sucrose, in
controlling flowering time.
Sucrose
Although sucrose has long been proposed to be a signal
molecule, it has been difficult to provide direct evidence because
this sugar is metabolized to monosaccharides, especially
glucose. However, the effects of glucose on plant processes
are generally different from those of sucrose. Whereas glucose
affects mainly seedling growth, photosynthesis, starch
degradation, and senescence, sucrose is more closely associated
with maturation, such as the processes of flowering and the
development of storage organs (Tognetti et al. 2013).
Sucrose influences plant size by promoting cell division in
apical meristems (Menges et al. 2006). It also drives the
horizontal growth of stolons in grass species (Willemoes et
al. 1988) and induces storage organ development by modulating
gibberellins (Xu et al. 1998).
Seed development is also controlled by sucrose. Addition
of this sugar to the mitotically active cotyledons of Vicia
faba (broad bean) stimulates the accumulation of starch,
whereas hexoses maintain cell division (Weber et al. 1996).
Elongation of radicles in the somatic embryos of Daucus
carota (carrot) is inhibited by a high concentration (>5%) of
sucrose, but not by hexoses and osmotica (Yang et al. 2004).
Increased expression of Sucrose Transporter (SUT) is
thought to play an important role in the sucrose signal (Yang
et al. 2004).
REVIEW ARTICLE
1
These two authors contributed equally to this work.
*Corresponding author; Gynheung An; Jong-Seong Jeon
Tel : +82-31-201-3471
E-mail : genean@khu.ac.kr; jjeon@khu.ac.kr
@Phil_Robichaud
@deepthiw
@JoseServera