ISSN 1021-4437, Russian Journal of Plant Physiology, 2016, Vol. 63, No. 2, pp. 204–209. © Pleiades Publishing, Ltd., 2016.
Original Russian Text © G.A. Sanadze, A.A. Davituliani, S.Sh. Pkhachiashvili, 2016, published in Fiziologiya Rastenii, 2016, Vol. 63, No. 2, pp. 218–224.
Biological Role for Synthesis and Release of Isoprene
by Photosynthesizing Cells in View of the Entropy Phenomenon
G. A. Sanadze
, A. A. Davituliani
, and S. Sh. Pkhachiashvili
Georgian National Academy of Sciences, pr. Rustaveli 52, Tbilisi, 0108 Georgia
Ivane Javakhishvili Tbilisi State University, Tbilisi, 0179 Georgia
Georgian Technical University, Tbilisi, 0175 Georgia
Received August 12, 2015
Abstract—In this review, the issues of photobiological synthesis and release of isoprene by chlorophyll-con-
taining cells are considered from the viewpoint of thermodynamics of open nonequilibrium systems, with an
emphasis on fundamental significance of the entropy phenomenon. The excretory function of the living cell
is envisioned as a result of the total release of energy by dissipative structures. The living cell metabolism rep-
resents a continuous transformation of a huge number of biologically significant chemical substances. The
complex of these transformations results in maintenance of cell homeostasis. The cell functioning can be
viewed as energy f lows and matter conversions occurring on biological matrices. The flows of irreversible
metabolic reactions proceed under steady-state condition of the system and ensure its balanced disequilib-
rium. The hypotheses considered in this review are based on the principles of energy dynamics; they permit
the description of cell metabolism from the laws of nonequilibrium thermodynamics of open systems. It is
concluded that the biogenic release of isoprene ensures entropy dissipation, which is required for regulation
of fluxes leading to the formation of terpenoids and allowing the maintenance of cell homeostasis.
Keywords: plants, isoprene effect, entropy, dissipative structure, energy dynamics, negative entropy
In the mid 1950s at the Institute of Botany of the
Georgian Academy of Sciences, a photobiological phe-
nomenon called “isoprene effect” (IE) was discovered
[1, 2]. The phenomenon consists in the ability of pho-
tosynthesizing leaves of some plant species to synthesize
and release molecular isoprene into the environment. It
was shown later that synthesis and emission of isoprene
also occurs in heterotrophic cells of plants and animals
(including humans), as well as in microorganisms. The
widespread natural occurrence of “dark” isoprene bio-
synthesis and isoprene release indicates that this process
is a fundamental property of living cells and that the iso-
prene effect is a specific type of this process observed in
Considerable interest in the study of biogenic iso-
prene emerged in the early 1990s. It should be noted
that these studies were focused on the mechanism of
isoprene formation in the light. This period was
marked by the appearance of first hypotheses on bio-
logical significance of isoprene emission. In 1995,
Sharkey and Singsaas published a paper with a provoc-
ative title: “Why plants emit isoprene” .
Presently, there are four answers to this question:
(1) According to the hypothesis of thermotolerance by
Sharkey et al. , the photobiosynthesis of isoprene
protects plant leaf chloroplasts from heat damage.
(2) Loreto et al.  proposed the antioxidant function
of isoprene biosynthesis; according to this hypothesis,
the cells fulfill nitric oxide reduction, similarly to the
processes occurring in the Earth’s atmosphere.
(3) According to the hypothesis of Rosenstail et al. ,
the cells possess a regulatory valve for the removal of
the phosphate bond energy contained in the isoprene
precursor, dimethylallyl diphosphate (DMADP).
(4) According to the hypothesis of Sanadze et al. 
chlorophyll-containing cells expel the excess free
energy in the form of isoprene as a participant of ter-
penoid synthesis, because DMADP is a precursor of
terpenoids and molecular isoprene.
It should be noted that the above hypotheses
describe various aspects of the cellular energy metabo-
lism. To understand the origin of biogenic isoprene for-
mation, at least two questions should be answered:
(1) why do the cells synthesize free isoprene and
(2) what is the cause for isoprene emission from the cell.
Abbreviations: deS—entropy dissipation; DMADP—dimethylal-
lyl diphosphate; DOXP/MEP—deoxyxylulose phosphate–meth-
ylerythritol phosphate pathway; IE—isoprene effect (emission)