ISSN 1021-4437, Russian Journal of Plant Physiology, 2008, Vol. 55, No. 1, pp. 115–118. © Pleiades Publishing, Ltd., 2008.
Desiccation is harmful for many reasons for higher
plants and cryptogams. Lichens are survivors of
extreme habitats where they are either desiccated or
rehydrated. Most lichens are desiccation-tolerant. They
survive prolonged periods in a metabolically inactive
state when the water content of their thallus drops
below than 10% of their dry weight .
Investigations on desiccation-tolerance show that
additional protective mechanisms are involved. Polyols
like ribitol, arabitol, and mannitol as well as nonreduc-
ing sugars such as trehalose and sucrose, might play
such a role . Glutathione, a redox buffer, also proba-
bly acts as both an antioxidant and a protectant for the
protein thiol groups in desiccated lichens .
On the other hand, abscisic acid plays an important
role in desiccation tolerance. Under drought conditions,
ABA is synthesized in plant tissues, sent to the guard
cells as a stress signal  and causes stomatal closure
. In addition, ABA increases desiccation tolerance of
embryonic tissues in poikilohydric angiosperms and
the xerophilic liverworts . Interestingly, contrary to
higher plants, ABA content in lichens increases after
hydration of air-dried lichen thallus and decreases dur-
ing its desiccation; moreover ABA could be a signal
that increases the tolerance of phycobiont .
: PA—polyamines; put—putrescine; spd—spermi-
This text was submitted by the authors in English.
In higher plants, polyamines (PAs) are also impli-
cated in a wide range of growth and developmental pro-
cesses and their metabolism is modiﬁed under some
environmental stress conditions such as mineral nutri-
ent deﬁciencies, drought stress, osmotic stress, salinity,
ozone, chilling, and UV light . PAs, low-molecular
weight polycationic compounds, at physiological pH
are able to bind to negatively charged molecules, such
as DNA, proteins, and membrane phospholipids  and
they could help to prevent stress-induced damages. The
relation of PAs to abiotic stress was ﬁrstly documented
by putrescine (put) accumulation in response to subop-
timal potassium levels in barley . In most cases, put
accumulation is accompanied by a relatively small
increase in spermidine (spd) and spermine (spm) levels.
Such results suggest that the levels of spd and spm are
homeostatically regulated . In addition, the rise in
spd and spm, but not put, related to these situations
could contribute to stabilization of membranes and
macromolecular constituents under drought and high-
temperature stresses [10, 11].
Compared with higher plants, little information is
available on mechanisms of desiccation tolerance in
lichens. Although PAs and ABA have been extensively
studied to clarify water stress response of higher plants,
their role in lichens has been rather neglected.
This paper aims to relate the PA and ABA metabo-
to their dissimilar tolerance to desiccation. Both
lichens are desiccation-tolerant and survive long time
Abscisic Acid and Polyamine Contents in the Lichens
D. Unal, A. Senkardesler, and A. Sukatar
Department of Biology, Faculty of Science, Ege University, Bornova, Izmir, 35100 Turkey;
Received March 6, 2006
—The levels of endogenous abscisic acid and total polyamine contents (putrescine and spermidine)
were studied in two lichen species differing in desiccation tolerance. ABA and polyamine contents showed sig-
niﬁcant differences between air-dried and water-treated thalli of
The levels of putrescine (put) and spermidine (spd) in water-treated
thalli were found higher
than in dry samples. The values for spd were almost threefold and for put almost 1.4-fold higher than in air-
dried samples. The levels of put and spd in water-treated
were lower than in the air-dried samples.
The lowest values for spd and put were almost 33-fold and 2.8-fold less, respectively. ABA contents of water-
increased by 2.65% and 25.5% when compared with air-dried thallus.
Key words: Pseudevernia furfuracea - Ramalina farinacea - abscisic acid - desiccation - lichens - polyamines -