ISSN 1021-4437, Russian Journal of Plant Physiology, 2009, Vol. 56, No. 2, pp. 154–163. © Pleiades Publishing, Ltd., 2009.
Original Russian Text © N.I. Aleksandrushkina, A.V. Seredina, B.F. Vanyushin, 2009, published in Fiziologiya Rastenii, 2009, Vol. 56, No. 2, pp. 170–180.
Studies on programmed cell death (PCD) in plants
develop in three main lines related to the following top-
ics: (a) terminal cell differentiation, with a classical
example of tracheal element formation; (b) wilting
(senescence); and (c) induced resistance to various
infections (so called hypersensitive response).
Wilting (senescence) is a terminal stage of leaf
development. This process is important for further
development of the whole plant, because it does not
mean just cell degeneration but also involves recircula-
tion of nutrient substances and their relocation toward
young leaves, developing seeds, and storage tissues.
Numerous investigations in physiology, biochemistry,
and molecular biology of leaf senescence have shown
that senescence is accompanied by concerted changes
in cell architecture, metabolism, and gene expression.
One of the earliest and most profound changes in the
senescing leaf is a massive destruction of chloroplasts.
This event strongly affects both the cell metabolism and
the leaf physiological role. The carbon assimilation
(photosynthesis) is replaced by chlorophyll catabolism
and degradation of macromolecules (nucleic acids, pro-
teins, and lipids), which converts the leaf from the
source of photosynthates to the source of mobilizable
nutrient substances .
Degradation of nucleic acids is integrated into the
process of leaf senescence and allows for differential
turnover of individual mRNAs, tRNAs, or rRNAs
throughout leaf senescence. At ﬁnal stages of leaf
senescence, this process occurs on a dramatic scale,
breaking down the major part of RNA and DNA [2, 3].
Endonuclease Activities in the Coleoptile and the First Leaf
of Developing Etiolated Wheat Seedlings
N. I. Aleksandrushkina
, A. V. Seredina
, and B. F. Vanyushin
Belozersky Institute of Physical and Chemical Biology, Moscow State University, Moscow, 119991 Russia;
fax: 7 (495) 939-3181; e-mail: email@example.com, firstname.lastname@example.org
Institute of Agricultural Biotechnology, Russian Academy of Agricultural Sciences,
Timiryazevskaya ul. 42, Moscow, 127550 Russia
Received January 23, 2008
— DNase activity in coleoptiles and the ﬁrst leaf apices of winter wheat (
cv. Mironovskaya 808) etiolated seedlings was found to increase signiﬁcantly during seedling growth, peaking
on the eighth day of plant development. The maximum of DNase activity was coincident with apoptotic inter-
nucleosomal DNA fragmentation in these organs. Wheat endonucleases are capable of hydrolyzing both single-
and double-stranded DNA of various origins. The leaf and coleoptiles were found to exhibit nuclease activities
that hydrolyzed the lambda phage DNA with N
-methyladenine and 5-methylcytosine more actively compared
to the hydrolysis of similar unmethylated DNAs. Thus, the endonucleases of wheat seedlings are sensitive to the
methylation status of their substrate DNAs. The leaves and coleoptiles exhibited both Ca
- and Zn
dent nuclease activities that underwent differential changes during development and senescence of seedling
organs. EDTA at a concentration of 50 mM fully inhibited the total DNase activity. Electrophoretic heteroge-
neity was observed for DNase activities operating simultaneously in the coleoptile and the ﬁrst leaf at different
stages of seedling development. Proteins exhibiting DNase activity (16–80 kD mol wt) were revealed in the ﬁrst
leaf and the coleoptile; these proteins were mostly nucleases with the pH optimum around 7.0. Some endonu-
cleases (mol wts of 36, 39, and 28 kD) were present in both organs of the seedling. Some other DNases (mol
wts of 16, 56, and about 80 kD) were found in the coleoptile; these DNases hydrolyzed DNA in the nucleus at
terminal stages of apoptosis. Different suites of DNase activities were revealed in the nucleus and the cyto-
plasm, the nuclear DNase activities being more diverse than the cytoplasmic ones. Thus, the cellular (organ-
speciﬁc) and subcellular heterogeneity in composition and activities of DNases has been revealed in wheat
plants. These DNases undergo speciﬁc changes during seedling development, serving at various stages of pro-
grammed cell death in seedling tissues.
Key words: Triticum aestivum - programmed cell death - senescence - endonucleases
: PCD—programmed cell death; PMSF—phenyl-
methylsulfonyl ﬂuoride; SSP-nuclease—single-strand-preferring