ISSN 10214437, Russian Journal of Plant Physiology, 2014, Vol. 61, No. 3, pp. 289–297. © Pleiades Publishing, Ltd., 2014.
Sugars provide energy and carbon skeletons for
plant growth and also behave as signaling molecules
[1, 2]. Sucrose, an essential photosynthesis product, is
the primary sugar transported in various vascular
plants. Sucrose is converted by sucrose synthase into
UDPglucose and fructose or by invertase into glucose
and fructose to support tissue development and func
tioning . Consequently, free fructose is phosphory
lated by hexokinase (HXK, EC 18.104.22.168) or fructoki
nase (FRK, EC 22.214.171.124) for further metabolism. How
ever, fructose is primarily phosphorylated by FRKs
because the affinity of FRKs for fructose is much
higher than that of HXKs .
Plant FRK enzymes have been purified from
, soybean, maize, sugarcane, etc. and analyzed
[5, 6]. FRK genes have been identified from several
plants, such as tomato and citrus . Tomato is the
first plant species, from which four FRK genes,
This text was submitted by the authors in English.
, were isolated and characterized [8–11].
Among these genes,
major FRKencoding genes expressed in most tissues,
exhibits the highest expression in
leaves and apices.
is required for stem xylem
development as well as sugar metabolism [12, 13].
and their corresponding isozymes are
found in tomato fruits .
expressed in stamens .
is located on chro
– on chromosome 6,
on chromosome 2,
– on chromosome 10
. Subcellular analysis showed that LeFRK3 is
located within plastids, whereas LeFRK1,
LeFRK4 are located in the cytosol. Hence, fruc
tose phosphorylation is not confined to special intrac
ellular localizations .
Different expression patterns were also exhibited
by four apple FRK genes
had similar expression patterns,
was expressed significantly higher in
shoot tips than in mature leaves.
highly expressed in young fruits than in mature fruits.
had a significant function in the efficient uti
lization of fructose in shoot tips and young fruit.
might provide fructose for sucrose synthesis
Isolation and Induced Expression of a Fructokinase Gene
Q. P. Qin, Y. Y. Cui, L. L. Zhang, F. F. Lin, and Q. X. Lai
School of Agriculture and Food Science, Zhejiang Agriculture and Forestry University, Lin’an, Hangzhou, 311300 China
The Key Laboratory for Quality Improvement of Agricultural Products of Zhejiang Province, Zhejiang A&F University,
Lin’an, Hangzhou, China;
fax: 08657163741276; email: firstname.lastname@example.org, email@example.com
Received January 29, 2013
—Fructose is essential for plant development as well as for fruit sugar composition and fruit quality.
Fructose is one of the major sugars in the mature loquat (
Lindl.) fruit, which is popular
because of its flavor and availability in early summer. The elucidation of the mechanism of fructose metabo
lism is of great importance for fruit quality improving. Fructose is primarily phosphorylated by fructokinase
(FRK). In order to understand the fructose metabolism in the loquat fruit, a putative loquat FRK fulllength
cDNA designated as
was isolated in this study. The
encoding FRK possesses conserved regions
inherent to plant FRKs. Transient expression of 35S:
GFP fusion protein in onion epidermal cells
was mainly expressed in the cytosol. The realtime RTPCR analysis indicated that
was expressed in all loquat tissues. Monitoring the dynamic changes of
transcripts and FRK
enzymatic activities demonstrated that
expression was at a relative high level during early fruit devel
opmental stages and dropped to the lower level during maturation, similar with the changes in FRK activity,
which was opposite to the fructose levels during fruit development. The results indicated that the high FRK
enzymatic activity was not conducive to fructose accumulation in loquat fruit. The
transcript level in
leaves of loquat seedlings was significantly enhanced after 6 h of treatment with 10 and 100 mM fructose or
glucose, which indicates that
is modulated by fructose and glucose in vivo.
Keywords: Eriobotrya japonica
, fructokinase, glycolysis, sugar metabolism
: DAF—days after flowering; FRK—fructokinase;
RACE—Rapid Amplification of cDNA Ends; SDH—sorbitol
dehydrogenase; S6PDH—sorbitol6phosphate dehydrogenase.