1022-7954/04/4002- © 2004
Russian Journal of Genetics, Vol. 40, No. 2, 2004, pp. 186–192. Translated from Genetika, Vol. 40, No. 2, 2004, pp. 248–255.
Original Russian Text Copyright © 2004 by Usatov, Razoriteleva, Mashkina, Ulitcheva.
Reversion analysis is one of the classical methods of
modern genetics. Reverse mutations of nuclear and
mitochondrial genes have been a subject of extensive
studies [1–4], while plastid genetics still rarely employs
reversion analysis. However, Imai  considered the
possibility of reverse mutations in the plastome of
higher plants as early as in 1937. In the 1960s, genera-
tion of green zones on white shoots of variegated plants
was observed in several studies [6, 7]. Michaelis 
assumed that green zones result from reversion of plas-
tid mutations. Samsonova and Bettkher [9–12] ana-
lyzed mutability of the Pl-alb1 plastome mutant of
tomato in a series of articles.
Several reasons may explain why only a few works
have focused on reversion analysis of plastid genes in
higher plants. First, it is rather difﬁcult to isolate cyto-
plasmic mutations, because cytoplasmic genome cop-
ies are multiple, organelle sorting out is time-consum-
ing , and selection of organelles takes place at sev-
eral levels . “Polyploidy” of the organellar genome
complicates construction of adequate experimental
models and development of methods to detect rever-
sions. Second, strictly maternal inheritance of the
organellar genome in most higher plants makes it
impossible to combine the cytoplasmic genes of both
parents in one zygote and, consequently, to employ the
standard methods of hybrid analysis like in the case of
nuclear genes . An additional difﬁculty is that sup-
pressor mutations may arise in the nuclear genome or in
the genome of another organelle .
Still, reversion analysis is necessary for detailed
analysis of the nature of cytoplasmic mutations and the
mechanisms of their interaction with the nuclear
genome. The objective of this work was to genetically,
morphologically, and physiologically study the sponta-
neous and nitrosomethylurea-induced revertants from a
collection of plastid chlorophyll mutants of sunﬂower.
MATERIALS AND METHODS
We used plants of sunﬂower
inbred line (obtained in 1959 by A.I. Gundaev on the
basis of population VNIIMK 20044 characterized by in
termediate maturation rate and high oil content); plas-
tome chlorophyll mutants en:chlorina-3, 5, and 7; green
revertants r-en:chlorina-3, 5, and 7; and partial rever-
tants pr(1–9)-en:chlorina-7, which preserved the
mutant leaf color and restored several habitual charac-
Construction and the nature of chlorophyll mutants
en:chlorina-3, 5, and 7 were described previously .
Revertants r-en:chlorina-3 and 5 were found in the cor-
responding mutant lines propagated strongly by self-
pollination for 20 and 11 years, respectively. Revertant
r-en:chlorina-7 was isolated from M
after seeds of line
en:chlorina-7 were treated with 0.02% nitrosomethy-
lurea (NMU) at 22
C for 18 h, washed for 30 min, and
M caffeine. Partial revertant
pr(1–9)-en:chlorina-7 were isolated from M
seeds of line en:chlorina-7 were treated with 0.02%
NMU at 22
C. The type and year of generation are
shown for each genetic line in the ﬁgure.
In hybrid analysis, revertants were reciprocally
crossed with the corresponding en:chlorina mutants
and with plants of the original line 3629; F
plants were examined.
At complete ripeness, plants were tested for height,
head weight, weight of seeds from one head, and
weight of 1000 seeds. At budding, chlorophyll a + b
content was estimated in medium-stratum leaves .
All ﬁeld measurements were carried out in 2001.
Spontaneous and Nitrosomethylurea-Induced Reversions
in Plastome Chlorophyll Mutants of Sunflower
A. V. Usatov, E. K. Razoriteleva, E. V. Mashkina, and I. I. Ulitcheva
Institute of Biology, Rostov-on-Don State University, Rostov-on-Don, 340090 Russia
Received January 28, 2003
—Spontaneous and induced revertants obtained from plastome chlorophyll mutants of sunﬂower were
subjected to genetic analysis. The mechanism of reversion (nuclear suppression, plastid suppression, true rever-
sion, or mitochondrial suppression) of the plastid mutation was shown to affect the degree of restoration of mor-
phological and physiological traits of sunﬂower plants.