生态环境 2006, 15(6): 1258-1263
Ecology and Environment
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Emission and utilization of methanol in higher plants
YANG Yueqin, YI Xianfeng*
College of Agriculture, Henan University of Science and Technology, Luoyang 471003, China
Abstract: Methanol, as one of the major volatile organic compounds (VOCs) found in the atmosphere, has been proved to be emitted
from leaves of most plant species. The formation, emission and metabolism of methanol in higher plants were reviewed in this paper.
Photosynthetic processes and chlorophyll a fluorescence parameters were measured on peony leaves treated with different methanol
concentrations. The primary results revealed that photosynthesis was greatly improved by methanol, as indicated by higher photosynthetic rates and stomata conductance (GS). Strikingly different patterns were observed for photochemical quenching (qP),
non-photochemical quenching (qN and NPQ), and electron transport rate (ETR). Decreases in Fm/Fo, Fv/Fo and PSII caused by
methanol revealed dual effect of methanol (stimulation or inhibition) on the peony leaves, which were determined by the concentration of methanol and time duration. The data suggested that methanol can not only serve as carbon source, but also regulate energy
distribution and dissipation, especially for non-photochemical quenching and photorespiration.
Key words: methanol; emission and utilization; photosynthesis; chlorophyll a fluorescence; peony
CLC number: Q945.11
Document code: A
Article ID: 1672-2175（2006）06-1258-04
We firmly know that plants produce a great deal
of volatile organic compounds (VOCs)[1-5]. These
VOCs play a number of important roles in plant
physiology, plant-herbivore & plant-microorganism
relationships, and in pollination and adaptation to abiotic factors[6].
As one of the major VOCs found in the atmosphere, methanol (CH3OH) has been proved to be a
natural product of plant metabolism and evidenced to
emit it from leaves of most plant species. Despite the
fact that methanol emissions have been relatively difficult to describe accurately, it has now been clear that
a large amounts of methanol are released from plants
substantially[7-8]. It has documented that all C3 plants
emitted substantial amounts of methanol under natural
conditions. Young leaves are found to emit much
more methanol than fully expanded leaves, sometimes
-1 g dry wt-1[5].
Fall and Benson[9] estimate the total amounts of
methanol emitted from plants to the atmosphere to be
greater than 0.1 billion ton globally, similar to that of
monoterpenes [5].
The exact pathway for methanol formation in
plants is not yet clear, however one hypothesis is put
forward that pectin methyl esterase (PME) accounts
for methanol emission during cell wall growing, especially during the formation of the intercellular spaces
of leaves[8]. Obendorf et al. [10] suggested that methanol was a byproduct of demethylation of pectin constituents catalyzed by pectin methyl esterase [11-12] in
the wall of meristomatic cells during their differentiation (Figs. 1 and 2). Alternatively, Ander et al. [13]
stated that methanol can be formed from enzymatically degradation of methyl ether groups of lignin by
the action of methylotrophic bacteria and fungi in the
plant cell wall[14-16].
Field and lab experiments evidenced that leaf
methanol emission rates are primarily consistent with
stomata activities. For example, field experiments
with sweetgum (Liquidambar styraciflua) saplings
conducted by MacDonald and Fall[7] indicated that
leaf methanol fluxes paralleled changes in stomatal
conductance over the course of the day. In lab experiments, methanol emissions from bean (Phaseolus
vulgaris) leaves decreased to very low levels after
stomata were induced to close by cutting the petiole or
administering abscisic acid[8]. These data suggest that
free methanol contained in the leaf air space exits
leaves along with transpired water vapor through stomata (Fig. 3). However, others postulated that some
基金项目：河南科技大学人才科研基金项目（2006ZY005）；中国科学院王宽诚博士后工作奖励基金资助
作者简介：杨月琴（1975－），女（藏族），实验师，硕士，研究方向为植物生理生态学。
*通讯作者：易现峰（1975－），男，副教授，博士，研究方向为生态学。Tel: +86-379-64282340；E-mail: yxfeng1975@126.com
收稿日期：2006-05-31
杨月琴等：高等植物对甲醇的释放和利用
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Fig. 1 Portion of a pectin polymer chain. G represents galacturonic
acid, R denotes rhamnose, and the solid branched lines indicate arabinogalactan side-chains (introduced from Galbally and Kirstine [17])
An early work of Cossins[18] showed that plants
can metabolize 14C-methanol into 14C-carbon dioxide,
organic acids, sugars, lipids, insoluble residues and
amino acids, mainly methionine and serine. With the
help of 14C-methanol labeling, Colas des Francs-Small
et al. [19] postulated that metabolic pathway of methanol in higher plants was estimated to be stepwise oxidation and successive formation of formaldehyde,
formic acid and carbon dioxide (Fig. 4). The fast
metabolic transformation of methanol into CO2 and
the subsequent assimilation of CO2 by the photosyn-
Fig. 2 Possible pathway for the formation of methanol from pectin (introduced from Galbally and Kirstine [17])
methanol
Methanol formation during cell
wall growth
Free water in inter-cellular cavity
Gas phase
sub-cuticular cavity
Conversion to formaldehyde by methanol oxidase
Methanol
release
to
atmosphere
Plant surface
with stomata
The release pathway of methanol from leaves (introduced from Galbally and Kirstine [17])
Fig. 3
CH3OH
HCHO
C1-folate pool, serine, methionine,
purines, thymidylate
HCOOH
CO2
Calvin-Benson cycle
Fig.4 Methanol metabolism in plants and other organisms (introduced from Fall and Benson [9])
methanol might be emitted from the cuticular surface[7], because a small fraction of the methanol
(3%~6%) released from the non-stomatal surface in
the hypostomatous leaves[8]. Despite methanol diffuses through the cuticle, the level of release is low
compared with those released via stomata.
thetic Calvin-Benson cycle, was an explanation of the
possible stimulating methanol role on biomass production[9]. By 13C-NMR analysis, Gout et al.[20] further demonstrated that the carbon atom of methanol is
also found in a variety of methyl groups, e.g. in those
of methionine and phosphatidylcholine. One of the
生态环境 第 15 卷第 6 期（2006 年 11 月）
1260
enzymes of this pathway, formate dehydrogenase, is
known to occur in a variety of plant tissues[21], and is
especially abundant in mitochondria of non-photosynthetic tissues[19, 22]. However, to date, the identity
of enzymes that oxidize methanol to formate in plants
is unclear. Holland and Polacco [16] found that plant
surfaces provide an ecological niche for
pink-pigmented, facultative methylotrophs (PPFMs),
which is responsible for activity of methanol dehydrogenase (or oxidase). It is reasonable to predict that
PPFMs may be closely related the oxidization process
of methanol to formate in higher plants.
1
of (1-qP) was calculated after Van Kooten and Snel
[26]. Before fluorescence measurements, leaves were
adapted to darkness for 20 min. The measurements of
photosynthetic and fluorescence parameters took no
more than 30 minutes as a whole.
2
Results and Analysis
2.1 Changes of photosynthesis of peony leaves
treated with different methanol concentrations
As shown in Table 1, Photosynthetic rate of peony leaves treated with different methanol concentrations increased significantly compared with the control, with the effect of 15% methanol most evident (t =
3.769, df = 29, P = 0.001). Application of different
methanol concentrations also apparently enhanced
stomata conductance of peony leaves (Table 1). 2%
methanol treatment increased stomata conductance
1.75 times more than the control (t = 2.296, df = 29, P
= 0.029). Correspondent with stomata conductance,
transpiration rates increased under the treatments of
methanol (Chi-Square = 11.207, df = 4, P = 0.024).
Slightly higher intercellular CO2 concentrations were
also observed when administrated different methanol
concentrations (Chi-Square = 2.884, df = 4, P =
0.208).
2.2 Changes of chlorophyll a fluorescence parameters of peony leaves treated with different
methanol concentrations
Fo and Fm increased with the application of different methanol concentrations, however, no significant changes were observed in PSⅡ photochemical
activity, i. e., Fv/ Fm (Chi-Square = 8.658, df = 4, P =
0.070) (Table 2). The maximum ratio of photochemical quantum yields and concurrent non-photochemical
processes, Fv/ Fo decreased along the methanol concentrations. ΦPSⅡ, which reflects the actual quantum
yield of electron transport in PSⅡ, decreased under
the treatment of methanol except for 15% (Table 2).
Different concentration of methanol inhibited electron
transport rate (ETR) except for 15% methanol.
Material and Methods
Peony (Luoyanghong, Paeonia suffruticosa L.)
leaves were evenly sprayed with 0% (distilled water),
2%, 5%, 8% and 15% methanol concentrations in natural condition between 10:00 and 11:00 am. Photosynthetic rate, stomata conductance (GS), transpiration rate and intercellular CO2 concentration were
measured using portable photosynthesis systems
(CIRA-1, PP Systems, Ltd., UK) 30 min after spraying on ternate top leaves with measurement light intensity 800 μmol·m-2·s-1. The measurement of Chl a
fluorescence induction and parameters was done at
ambient temperature by using a fluorescence monitoring system fluorometer (FMS-2, Hansatech Ltd.,
Norfolk, UK) as described by Rohacek and Bartak [23].
The minimal (dark) (Fo) and maximal (Fm) fluorescence yield were obtained with weak modulated light
(0.04 μmol·m-2·s-1) then with a 1 s pulse of saturated
light (8 000 μmol·m-2·s-1). The ratio of Fv/ Fm was
served as a measure of the maximum photochemical
efficiency of PSⅡ. The efficiency of energy conversion in PSII (ΦPSII), was calculated as
(Fm′-Fs)/Fm′( Fs=stationary level of fluorescence
emission, Fm′= maximum fluorescence during illumination) [24]. Photochemical quenching (qP) and
non-photochemical quenching (qN and NPQ) were
calculated according to Schreiber et al. [25]. The level
Table 1 Photosynthetic parameters of peony leaves treated with different methanol concentrations
Photosynthetic parameters
Treatments
Transpiration rate
/(mmol·m-2·s-1)
Stomata conductance
/(mmol·m-2·s-1)
Photosynthetic rate
/(μmol·m-2·s-1)
Intercellular CO2 concentration
/(×10-6)
Control
2% methanol
5% methanol
8% methanol
15% methanol
4.55  0.66
7.05  1.99
5.22  0.45
5.64  1.82
4.94  0.66
294.04 + 68.80
513.17  245.22
495.67  62.00
466.00  187.67
358.17  74.17
5.06  1.49
4.98  1.16
6.88  1.18
7.75  1.28
8.30  1.97
312.20  11.98
317.50  10.83
317.17  5.83
314.50  7.17
298.83  11.11
杨月琴等：高等植物对甲醇的释放和利用
1261
Therefore, dual effect of methanol (stimulation or inhibition) on the peony leaves was determined by the
concentration of methanol.
2.3 Changes in quenching coefficients of peony
leaves treated with different methanol concentrations
Photochemical quenching (qP) was increased by
8% and 15% methanol concentrations. Non-photochemical quenching (qN), proved to protect the photochemical apparatus against the destructive effects of
excess light energy [27], decreased under administration of methanol concentrations from 2% to 15%. The
photochemical quenching coefficient, (1-qP), indicating the estimated reduction state of PS II Van Kooten
and Snel[26] and photoinhibitory damage[28], decreased
under higher concentration treatments. 2-15% methanol
concentrations
significantly
decreased
non-photochemical quenching, qN and NPQ.
3
Discussion
Treatments with different methanol concentrations promoted stomata movement, consequently enhanced transpiration rate and stomata conductance
(Table 1). Increases of intercellular CO2 concentration
were observed when administrated with methanol,
which may be due to an increase in the availability of
CO2 via the cellular transformation of methanol[29],
and consequently a decrease in non-photochemical
energy dissipation was induced, which results in efficient nicotinamide adenine dinucleotide phosphate
(reduced) and adenosine triphosphate synthesis, benefiting photosynthetic accumulation. It was postulated
that methanol might be incorporated into carbon metabolism as a single carbon compound, likely formaldehyde and serine as primary products[20]. However, it
was worth to analyze relationship between the stimulatory effect of methanol on photosynthesis and the
photosynthetic activity parameters (Fv/Fm and ΦPSII).
As seen from Table 1 and 2, the increase in the photosynthetic rate induced by methanol was not followed
by an increase in the photosynthetic activity. And, the
PSII activity supported by the water splitting system
and the oxygen evolution was not significantly increased, even decreased (Table 2). Moreover, there
was no improvement in the PSII photochemical efficiency (Fv/Fm) compared with control. When compared with control, no increase was seen in fluorescence parameters concerning the PSII activity such as
the basal quantum yield of non-photochemical processes (Fo/Fm), the maximum ratio of photochemical
quantum yields and concurrent non-photochemical
processes (Fv/Fo), and the photochemical quenching
value (qP) under methanol-treated conditions (Table
2). However, we found that qP and NPQ, was strongly
competitively affected by methanol, which indicated
that methanol increases the energy transfer from PSII
to PSI at higher concentrations. Therefore, the improvement in the photosynthesis treated with higher
concentration methanol appeared to be related to the
alteration in energy dissipation processes associated
with the primary photosynthetic activity. Furthermore,
the discrepancy between stomata conductance and
transpiration rates and whether applied methanol can
decrease leaf temperature and depress respiration
needs further investigations.
In summary, the stimulatory effect of methanol
was found to be based on the increase in CO2 concentration in leaves, which resulted from methanol oxidative degradation in photosynthetic tissues [18, 29]. On
the other hand, the effect of methanol seems to change
the mechanism of energy distribution during photosynthesis and the final energy storage into Calvin cycle. Further studies are called for NPQ components,
Table 2 Chlorophyll a fluorescence parameters of peony leaves treated with different methanol concentrations
Chlorophyll fluorescence
Parameters
Control
2% methanol
5% methanol
8% methanol
15% methanol
Fo
Fm
Fv/Fo
Fv/Fm
ΦPSII
qP
qN
NPQ
ETR
36.50  1.33
243.17  14.17
5.68  0.44
0.85  0.01
0.18  0.03
0.35  0.08
0.79  0.03
2.08  0.22
61.42  8.7
40.67  1.33
268.83  7.22
5.61  0.12
0.85  0.00
0.13  0.01
0.24  0.01
0.57  0.03
1.71  0.20
53.76  5.4
37.00  2.67
244.50  11.17
5.64  0.27
0.85  0.01
0.16  0.02
0.31  0.02
0.60  0.02
1.63  0.18
63.21  6.5
39.83  1.50
247.00  4.00
5.22  0.23
0.84  0.01
0.16  0.03
0.36  0.04
0.63  0.04
1.65  0.24
68.17  4.2
40.33  1.56
248.83  8.17
5.18  0.18
0.84  0.00
0.21  0.02
0.41  0.04
0.60  0.01
1.57  0.09
47.87  8.0
Treatments
生态环境 第 15 卷第 6 期（2006 年 11 月）
1262
such as the energy-dependent quenching qE, the
state-transition quenching qT and the photoinhibitory
quenching qI. It appeared here that the effect of
methanol on peony was a complex of interactions between improvement of CO2 availability via photosynthesis and non-photochemical energy-dissipative processes. Emission and utilization of methanol in higher
plants should be highlighted in the near future.
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Acknowledgement: The study was supported by
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Wong Education Foundation, Hong Kong.
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高等植物对甲醇的释放和利用
杨月琴，易现峰
河南科技大学农学院，河南 洛阳 471003
摘要：植物可向大气中释放一种挥发性的有机气体——甲醇，同时对这种气体可加以利用。在详细阐述甲醇的产生、释放和
可能的代谢机制的基础上，通过不同浓度的甲醇溶液喷施牡丹叶片，测定其对光合作用过程及叶绿素荧光参数变化的影响。
结果表明，光合作用有较大改善：光合速率明显提高，气孔导度增加，叶内 CO2 浓度也有一定幅度改善。叶绿素荧光参数
（qN 和 NPQ）以及电子传递速率（ETR）发生较大改变；Fm/Fo，Fv/Fo 和PSII 的下降可能与甲醇对牡丹叶片的双向效应
（促进性和毒性）有关，这取决于喷施的浓度、次数和时间。初步的结果显示：甲醇提高光合作用速率的同时，并没有伴随
光合效率和机能的改善和提高。期间的气孔导度和胞内 CO2 浓度的提高以及非辐射能耗散（qN 和 NPQ）和光呼吸的降低可
能是牡丹叶片光合作用速率提高的主要原因。
关键词：甲醇；释放与利用；光合作用；叶绿素荧光；牡丹