Note: Descriptions are shown in the official language in which they were submitted.
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TITLE OF THE INVENTION
METHOD OF INCREASING PHOTOSYNTHESIS IN
PLANTS COMPRISING AN EXPOSURE THEREOF TO SALICYLIC
ACID AND COMPOSITIONS THEREFOR
FIELD OF THE INVENTION
The present invention relates to agriculture. More
particularly, the invention relates to a method of increasing
photosynthesis of a plant. In addition, the invention relates to a method
of increasing photosynthesis and/or yield in plants, comprising an
exposure thereof to salicylic acid, and compositions therefor.
BACKGROUND OF THE INVENTION
Salicylate plays a clear role in plant thermogenicity.
Cyanide resistant respiration is induced to generate heat in species
contained in a number of plant families (Meeuse & Raskin, 1988). SA
concentrations in the appendix of the Voodoo lily rise just prior to a
temperature rise in this organ, and application of SA can trigger a similar
temperature rise of up to 12°C (Raskin et al., 1987). SA may play a
role
in flowering: concentration in the phloem of cocklebur plants rises when
they are induced to flower through daylength manipulations (Cleland &
Ajami, 1974). However, benzoic acids and chelating agents can also
induce flowering in these plants, and levels of induced plants are not
always higher than those in vegetative plants (Raskin 1992). Currently,
the role of SA in the induction of systemic acquired resistance (SAR) is
a topic of intense research (Sticher et al., 1997). It has been shown that
when SAR is induced SA levels rise and SA, in conjunction with NO have
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been shown to play a role in hypersensitive response (Delledonne et al.,
1998). However, it has recently been shown that mutants, unable to
produce SA, are still able to develop SAR (Hunt & Ryals, 1996), leaving
the exact role of SA uncertain. Recent work conducted in the laboratory
of Smith, has shown that the chronic injection (Zhou & Smith, 1996) of SA
(10 mM from shortly after tasselling until physiological maturity) increases
the photosynthetic rate of corn plants (Zhou et al., 1999, J. Agron. Crop.
Science 183(2)). Photosynthetic rates have also been reported to rise
when plants are infected by symbionts, most notably rhizobia (Maury et
al., 1993), mycorrhizal fungi (Kucey & Paul, 1982) and plant growth
promoting rhizobacteria (PGPR) (Zhang et al., 1997). It has been shown
that inoculation with two species of PGPR in the genus Serratia improves
soybean growth and nodulation by a rapid (within one week) increase in
overall plant vigour, including an increase in photosynthesis (Zhang et al.,
1997). In addition, some PGPR produce a range of siderophores,
including SA. This SA has been thought to have a role in PGPR benefits,
at least as far as pathogen resistance is concerned (De Meyer & Hofte,
1997); however, recent evidence casts doubt on these results (Press et
al., 1997). Paultiz's group has measured elevated SA levels in plant
tissues following inoculation with PGPR known to minimize pathogen
effects. Earlier work (Dijak et al., 1985) showed that soybean plants can
be "tricked" into higher photosynthetic rates, but will down regulate the
process to its original level after a number of days. This has also been
observed where COZ fertilization is practiced in greenhouse settings
(Wulff & Strain, 1982). It seems that plants have a complex homeostatic
system to regulate their most important process.
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There thus remains a need to better understand the
workings of the complex homeostatic system which is involved in the
regulation of photosynthesis. Moreover, there remains a need to assess
the role of SA on photosynthesis of plants.
In view of asking fundamental questions relating to the
physiology of plants, the personnel of D. Smith's laboratory developed a
method for the chronic application of solutions into higher plants. While
methods for chronic applications (intravenous) have existed for animals
for over half a century, such a method had not existed before recently for
plants. This new system of injection for plants lead to testing of injection
effects of a number of physiologically important compounds, from sugar
to phytohormones. The effects of some of the phytohormones were not
what would have been anticipated from the published literature.
However, all previous literature involved relatively short applications
through various wounds in plant leaves and roots. For a period of over
a month, the injection of SA into the pith of the stem tissues of corn under
pressure was initiated to try to clarify the conflicting reports relative to
the
effect of SA on plant physiology. Surprisingly, an increase in the
photosynthetic rate was observed following this chronic injection of SA
into the stems of corn plants.
Unfortunately, however, the injection of plants only gives
a small indication of what would occur in the field or in more controlled
environment, should the application of SA be less direct, not chronic and
so forth. It should be understood that chronic injection in plants is an
artificial method and that results obtained therewith are not necessarily
predictable of routinely used methods and more natural methods of
application. In addition, it will be recognized that a chronic injection in
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corn is not a commercially feasible application method. There thus
remains a need to assess whether the results obtained with the artificial
application method of SA, by chronic injection of corn stems (Zhou et al.
1999, J. Agron. Crop Sc. 183(2)), can be reproduced with commercially
feasible types of application of SA to corn and whether an acute
application (as opposed to a chronic one) will also show the same type
of response to SA treatment. It also remains to be determined whether
plants other than corn could benefit from a treatment with an agricultural
composition comprising SA.
The present invention seeks to meet these and other
needs.
The present description refers to a number of
documents, the content of which is herein incorporated by reference in
their entirety.
SUMMARY OF THE INVENTION
The invention concerns the demonstration that spraying
of SA on the leaves of plants significantly increases the photosynthetic
rate thereof. The present invention therefore relates to compositions to
increase the photosynthetic rate of plants in general. In addition, the
present invention relates to methods of increasing the photosynthetic rate
of plants in general, comprising an application of an agriculturally effective
dose of SA. In a particularly preferred embodiment, the invention relates
to an acute application of SA to a spraying of the leaves of the plants and
to its effect on the yield of field grown plants.
While the present invention has been demonstrated
using corn and soybean, the invention should not be so limited. Indeed,
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it will be clear to a person skilled in the art to which the present invention
pertains, that corn and soybean, two evolutionary distant types of plants,
respond similarly to application of SA. Therefore, it is expected that other
types of plants should respond similarly to the SA application, by
5 displaying an increase in the photosynthetic rate and/or yield of plants.
Based on the evolutionary divergence of corn and
soybean, which both display an increased photosynthetic rate after SA
treatment, the present invention relates to compositions and methods for
different plant families such as Poaceae, Cucurbitaceae, Malvaceae,
Asteraceae, Chenopodiaceae and Solonaceae. More specifically, crops
within the scope of the present invention include without limitation corn,
cotton, cantaloupe, cucumber, canola, lettuce, potato and beet. Non-
limiting examples of crop plants also include monocot, dicot, members of
the grass family (containing the cereals), and legumes.
Thus, the present invention relates to agricultural
compositions comprising at least SA (and methods of using same) for
promoting photosynthetic rate increases and/or increase in yield of a
crop. It should be clear to a person skilled in the art that other
photosynthetic rate increasing-, and/or yield increasing compounds could
be added to the compositions of the present invention.
While the photosynthetic rate and/or yield enhancing
capabilities of the compositions of the instant invention are demonstrated
with corn and soybean, it is expected that other crops should also show
the same type of response to SA treatment. These plants include without
limitation significantly divergent plants in eight distinct families: (1)
corn,
the only monocot tested herein, in the family of grasses (Poaceae), which
also contains the cereals; (2) cucumber and cantaloupe, the latter being
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a plant used horticulturally, and being slow to germinate at low
temperature [its base temperature is about 14°C] (Cucurbitaceae); (3)
cotton, one of the most important fibre crops on the planet (Malvaceae);
(4) lettuce (Asteraceae); (5) beet (Chenopodiaceae); (6) potato, a very
important crop (Solonaceae, which also includes tobacco, peppers and
tomato); and two families of legumes (7) canola, representing the mustard
group (Brassicaceae) and (8) soybean (representative of oil seed crop),
bean (representative of a crop for human consumption) and red clover
and alfalfa (forage legumes) (all of the Fabaceae family).
In view of the evolutionary distance between corn and
soybean, and of the similar results obtained with these different crop
plants, it can be predicted that such results will apply to crop plants in
general. It follows that a person skilled in the art can adapt the teachings
of the present invention to other crops. Non-limiting examples thereof
include tobacco, tomato, wheat, barley, rice, sunflower and plants grown
for flower production (daisy, carnation, pansy, gladiola, lilies and the
like).
It will be understood that the compositions can be adapted to specific
crops, to meet particular needs.
BRIEF DESCRIPTION OF THE DRAWINGS
Having thus generally described the invention, reference
will now be made to the accompanying drawings, showing by way of
illustration a preferred embodiment thereof, and in which:
Figure 1 shows the effect of salicylic acid on
photosynthesis of soybean;
Figure 2 shows the effect of salicylic acid on percent
increase in photosynthesis of soybean;
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Figure 3 shows the effect of salicylic acid on leaf area
of soybean; and
Figure 4 shows the effect of salicylic acid on shoot dry
weight of soybean.
Other objects, advantages and features of the present
invention will become more apparent upon reading of the following
non-restrictive description of preferred embodiments with reference to the
accompanying drawing which is exemplary and should not be interpreted
as limiting the scope of the present invention.
DESCRIPTION OF THE PREFERRED EMBODIMENT
The present invention therefore demonstrates that the
application of SA to the leaves of soybean plants increases their
photosynthetic rates, leading to increased dry matter production. Thus,
the present invention provides a new method (and compositions therefor)
of increasing yield of plants and especially of soybean and corn.
Moreover, preliminary data show that an increase in yield following SA
treatment of soybean and corn, is also observable under field conditions.
The present invention is illustrated in further detail by the
following non-limiting example.
EXAMPLE 1
Effect of salicylic acid on photosynthesis of soybean
Materials and Methods
Salicylic acid:
Salicylic acid (analytical grade) was purchased from
Anachemia Science (Montreal, Canada). The Required amount of
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salicylic acid was dissolved in few drops of dimethyl sulfoxide and the
volume was made with distilled water to give a final concentration of
10-3M.
Plant Material:
Soybean (cv Bayfield) seed was surface sterilized with
2% sodium hypochlorite and germinated in autoclaved vermiculite.
Seedlings, at the two leaf stage, was transplanted into 7 inches plastic
pots containing promix. Pots were placed in a green house maintained
at 2212°C with a day/night cycle of 16/8h. Plants were watered as
required.
Salicylic acid treatment:
Twenty day old plants were sprayed with salicylic acid
solution until dripping, with an automizer (Nalgene, USA). Each plant
required about 5ml of spray solution. Plants sprayed with 0.02% Tween
20 served as the control. Each treatment was replicated three times and
organized on the green house bench in a randomized block design.
Data collection:
Photosynthesis of the second nodal leaf from the top
was recorded every 24h using a Li-Cor 6400 portable photosynthesis
system. Data were analyzed with Statistical Analysis System (SAS Inc.,
NC, USA). Percent increase in photosynthesis over the control was
calculated. Multiple means comparisons were conducted with an ANOVA
protected LSD test.
Results
Salicylic acid spray increased the photosynthesis of
soybean (Table 1, Figs.1 & 2) at 10-3M . The photosynthesis rate
increased from day 1 up to day 5 after which it decreased and reached
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levels not different from the control plants. Figures 3 and 4 show the
percent increase in photosynthesis of salicylic acid treated plants over
that of the control. Photosynthesis increased gradually and peaked at 4
days after treatment. Leaf area and shoot dry weight of treated plants
were higher than those of the untreated ones (Table 2, Figs. 4 & 5).
TABLE 1
Effect of salicylic acid on photosynthesis
(Nmol m-2 sec'') of soybean
Treatment Days after treatment
1 2 4 5 6
Control 11.2 8.1 10.1 12.1 10.4
Salicylic acid 13.8* 11.1 * 15.3 17.6 14.6*
(10-3M)
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TABLE 2
Effect of salicylic acid on leaf area and shoot
dry weight of soybean
Treatment Leaf Area Shoot Dry Weight
(cm2) (mg)
Control 188.0 951.6
Salicylic acid 202.6 985.5
(10-3M)
The data included herein demonstrate that an
application of SA to the leaves of soybean plants increases their
photosynthetic rates, leading to increased dry matter production. In
addition, field work has shown increases in both soybean and corn
relative to controls. These two species were chosen because they are
important crop plants in North America and because they are very
different in several ways. First, they are very distantly related. Soybean
is a dicot and corn is a monocot. In addition, the two crop species
represent the two most important photosynthetic physiologies, soybean
being a C3 plant and corn a C4 plant. Thus, it can be anticipated that the
enhancement of photosynthesis by SA application will be present in a
wide range of plants.
In some treatments, repeated applications of SA were
made and it was shown that the plant was able to respond to more than
one application of SA. At the time of this filing, quantitative data are not
yet available for the field-grown material but visual observations suggest
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large differences (more branches and more pods on each plant) for at
least soybean. Nevertheless, it appears that yield of corn is also
enhanced by the treatment of the present invention.
Although the present invention has been described
hereinabove by way of preferred embodiments thereof, it can be modified,
without departing from the spirit and nature of the subject invention as
defined in the appended claims.
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REFERENCES
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Cleland et al., 1974, Plant Physiol. 54:904-906.
Dijak et al., 1985, Env. Exp. Bot. 25:375-384.
Hunt et al., 1996, Crit. Rev. Plant Sci. 15:583-606.
Kucey et al., 1982, Soil. Biol. Biochem. 14:407-411.
Maury et al., 1993, Plant Phys. 101:493-497.
Meeuse et al., 1988, Sex Plant Reprod. 1:3-15.
Press et al., 1997, Am. Phytopath. Soc. 10:761-766.
Raskin et al., 1987, Science 237:1545-1556.
Raskin et al., 1992, Plant Physiol. 99:799-803.
Sticher et al., 1997, Ann. Rev. Phytopath. 35:235-270.
Wulff et al., 1982, Can. J. Bot. 60:1084-1091.
Zhang et al., 1997, Ann. Bot. 79:243-249.
Zhou et al., 1999, J. Agron. Crop. Sci. 18_ 3(2).
Zhou et al., 1996, Crop Science 36:452-456.
