ISSN 1062-3604, Russian Journal of Developmental Biology, 2009, Vol. 40, No. 6, pp. 339–344. © Pleiades Publishing, Inc., 2009.
Original Russian Text © N.V. Obroucheva, S.V. Lityagina, 2009, published in Ontogenez, 2009, Vol. 40, No. 6, pp. 419–424.
Studies of invertase (188.8.131.52) in different plant
organs and tissues have led to the discovery of two
invertases (Sturm, 1999) that are similar in their opti-
mum pH and reaction products (glucose and fructose),
but differ in their physiological role and location inside
the cell: cell wall invertase and vacuolar invertase
(Roitsch and Tanner, 1996). It is thought that the acid
invertase bound to cell walls is a key enzyme in the
phloem unloading (Roitsch et al., 2003) and breaks
down the sucrose delivered from photosynthesizing or
storage organs to the apoplast of a growing organ by
still unknown sucrose transporters. As a result of its
functioning, monosaccharide molecules can be used
directly in the synthesis of cell wall polymers, or deliv-
ered by the transporters of monosaccharides to the
cytoplasm and take part in metabolism.
Sucrose, if not hydrolyzed at the level of cell wall
and not involved in metabolism, is transported to vacu-
oles, where it can be stored in considerable amounts.
Vacuolar invertase can break it down into glucose and
fructose, which leads to the accumulation of endoge-
nous osmotica and an increase in osmotic pressure.
Vacuolar invertase can therefore play an important role
in water inﬂow to growing cells and, consequently, in
initiating growth during germination.
Vacuolar invertase is characterized by a less acidic
optimum pH (4.5 to 5.5) than that of cell wall invertase
(3.5 to 5.0). For example, the optimum pH of vacuolar
invertase in the carrot
(Unger et al.,
(Tang et al., 1996), and bar-
(Karuppiah et al., 1989) is from
0.6 to 0.9 units higher than that of cell wall invertase in
the same tissues. The substrate of both acid invertases
can be not only sucrose but other fructofuranosides
with terminal fructose residue (e.g., such oligosaccha-
rides as rafﬁnose, stachyose, and verbascose) as well.
Their hydrolysis occurs much more slowly than that of
sucrose (Sturm, 1999; Hashizume et al., 2003).
In general, much less attention has been given to
vacuolar invertase than to cell wall invertase. Acid vac-
uolar invertase activity has been found in numerous
plants, and its enzymatic features have been described.
It has been demonstrated on various plants that inver-
tase can exist in the form of several isozymes with dif-
ferent values for the Michaelis constant for sucrose but
with identical pH optima for various isoforms (Ober-
land et al., 1993; Hashizume et al., 2003).
Vacuolar invertase activity has been studied only in
orthodox seeds, i.e., common seeds that lose more than
90% of their water during maturation and are preserved
in this dry state until they are sown. As a rule, the vac-
uoles in them are transformed into storehouses of
reserve protein in parallel with water loss; the vacuoles
are restored during imbitition, absorbing water, and
then act as osmotic compartments. The synthesis of
invertase protein de novo has been demonstrated in
seeds of the lettuce
Acid Vacuolar Invertase in Dormant and Germinating
Seeds of the Horse Chestnut
N. V. Obroucheva and S. V. Lityagina
Institute of Plant Physiology, Russian Academy of Sciences, ul. Botanicheskaya 35, Moscow, 127276 Russia
Received April 22, 2009; in ﬁnal form, May 27, 2009
—A high water content is maintained in the tissues of the axial organs of horse chestnut seeds after
the fruit is shed and down to the time the seeds germinate. The plant cell vacuoles, features of whose metabolism can
inﬂuence the cells’ preparation to initiate growth in germination, are preserved. It was shown that the activity of acid
invertase and its capacity to hydrolyze both sucrose and rafﬁnose remain stable throughout the period of dormancy
and the transition to germination, as do the molecular weight of its subunits (63 and 65 kDa) and multimer (500 to
550 kDa). The activity of the enzyme increases when the seeds swell under optimal conditions for germination;
this is associated with the synthesis of new molecules of the enzyme in long-lived mRNA templates. The
storability of the enzyme in the vacuoles of dormant seeds, together with the increase in its activity when seeds
coming out of dormancy swell, ensures the rapid hydrolysis of sucrose issuing from the seeds’ cotyledons, thus
leading to increased osmotic pressure and, as a result, the beginning of cell elongation, i.e., germination.
, recalcitrant seeds, axial organs, vacuolar invertase, germination, vacu-
BIOLOGY OF PLANT DEVELOPMENT