Plant Science 150 2000 191 – 199
Physiology and growth of Douglas-fir seedlings treated with ethanol solutions
Gladwin Joseph
a
, Rick G. Kelsey
b,
a
Department of Forest Science, Oregon State Uni6ersity, Cor6allis, OR
97331
, USA
b
USDA Forest Ser6ice, Pacific Northwest Research Station,
3200
Jefferson Way, Cor6allis, OR
97331
, USA Received 17 May 1999; received in revised form 14 September 1999; accepted 14 September 1999
Abstract
Applying 1, 5, 10, and 20 solutions of ethanol to the roots of Douglas-fir Pseudotsuga menziesii [Mirb.] Franco seedlings three times a week was deleterious to their physiology and growth. Ethanol concentrations of 10 or higher were lethal within
a week of treatment initiation, while the 5 solution was lethal to seedlings at 8 weeks. Seedlings treated with the 1 solution were alive at 8 weeks, but showed signs of physiological decline. If Douglas-fir seedlings have a tolerance threshold for ethanol
solutions applied to their roots, it appears to be at a concentration below 1. Ethanol moved up the stems and into needles, yielding concentrations in the stems 9 times higher than in needles. Ethanol vapors in the atmosphere surrounding seedlings
readily diffused into needles, but not into stems. After 1 week of treatments, net photosynthesis, stomatal conductance, and transpiration declined as ethanol concentrations increased. However, seedlings treated with the control 0 and 1 ethanol
solutions had the same xylem water potentials, which were higher than for seedlings treated with the 5 solutions. High ethanol concentrations ] 1 may have damaged membranes involved in photosynthesis and stomatal function thereby causing the
observed decline in net photosynthesis and stomatal conductance. At concentrations ] 5, water uptake was impaired, suggesting that root membranes may have been damaged. © 2000 Elsevier Science Ireland Ltd. All rights reserved.
Keywords
:
Pseudotsuga menziesii; Gas exchange; Tolerance; Water potential; Toxicity www.elsevier.comlocateplantsci
1. Introduction
Ethanol is a product of anaerobic metabolism that occurs naturally in plant tissue in response to
hypoxia or anoxia [1]. Ethanol synthesis may al- low tissues to survive transient periods of oxygen
stress by supplying ATP [2], and by preventing cellular acidosis [3,4]. Ethanol is produced in roots
of flooded plants and diffuses into the surrounding water and soil [5], or is transported into the stem
and foliar tissues where it may be metabolized into cellular constituents [6 – 8]. However, ethanol can
be toxic if it accumulates to high enough concen- trations either in the rooting solution or in the
tissues [9,10]. The effects of ethanol on plant growth and
physiology are not consistent. It can either damage or stimulate growth depending on the concentra-
tions, species, and tissue. When tomato roots were fed 5 ethanol solution growth was reduced, and
solutions ] 10 were lethal [11]. In contrast, fo- liar applications of 15 – 20 ethanol solutions in-
creased
growth of
tomato Lycopersicum
esculentum Mill. by 18 [11]. Foliar applications of 1 – 10 ethanol solutions neither stimulated
growth nor caused any injury to Douglas-fir and ponderosa pine Pinus ponderosa Dougl. Ex
Laws. seedlings [12]. Mortality of chick pea Cicer arietinum L. seedlings increased as the length of
exposure to ethanol vapors increased in a static anaerobic atmosphere [13]. Cell growth and so-
matic embryogenesis of carrot
Daucus carota L. cell cultures were negatively affected at relatively
Corresponding author. Tel.: + 1-541-750-7368; fax: + 1-541-750- 7329.
E-mail address
:
kelseyrfsl.orst.edu R.G. Kelsey 0168-945200 - see front matter © 2000 Elsevier Science Ireland Ltd. All rights reserved.
PII: S 0 1 6 8 - 9 4 5 2 9 9 0 0 1 8 9 - 2
low concentrations 0.05 of ethanol [10]. How- ever, placing etiolated cuttings from mung bean
Vigna radiata L. into 0.1 ethanol solution stim- ulated root initiation and growth [14]. Root
growth also was enhanced by 50 when excised wheat Triticum aesti6um L. roots were treated
with 0.9 ethanol in light [15]. Pea plants were able to tolerate ethanol applied to their roots at
100 times the concentration 0.46 found in their xylem sap during flooding [9]. When cut stems of
Douglas-fir seedlings were supplied with ethanol concentrations 0.1 2 – 3 times the amount in
their stems under flooded conditions, there was no effect on stomatal conductance [5].
In our continuing effort to better understand the physiological and ecological implications of
ethanol synthesis and accumulation in conifers we were interested in determining how ethanol ap-
plied to the roots would affect growth and physi- ology of Douglas-fir seedlings. Since foliage of
Douglas-fir is apparently capable of metabolizing ethanol [5], we hypothesized that shoot biomass
might increase with some concentrations of ethanol. Additionally, by using a wide range of
ethanol concentrations we attempted to establish a tolerance threshold for ethanol applied to Dou-
glas-fir roots. Finally, we hypothesized that detri- mental concentrations of ethanol would affect
membrane bound processes such as photosynthesis [18],
stomatal conductance
via guard
cell metabolism, and water uptake because ethanol
toxicity is potentially associated with membrane damage [9,16,17]. Since guard cell metabolism is
linked to membrane bound processes [19], stom- atal conductance would decline if ethanol damages
the guard cell membrane. A decline in water po- tential in ethanol treated seedlings compared to
controls under similar vapor pressure deficits would indicate damage to roots and a reduction in
water uptake.
2. Material and methods
