Thig Mo Nasty
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Transcript of Thig Mo Nasty
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7/31/2019 Thig Mo Nasty
1/2
Cahilog, Ma. Reza
Garcia, Bea Clarise B.
Tueres, Alyssa Nicole
Plant Movements
Thigmonasty refers to the non-directional
response of a plant to :
touch flexure vibration blowing slight heat chemical stimulus electrical stimulus lack of water
which results to the rapid loss of water from its turgid
motor cells. This loss of turgidity then causes the leaf to
temporarily droop downwards. Makahiya is a good
example of a plant which exhibits thigmonasty.
Figure 1. Makahiya leaves before (left) and after (right)
stimulation of leaves.
Makahiya (Mimosa pudica Linn.) is a commonly
known weed having compound leaves and pink
inflorescences. Here are the parts of the makahiya
exhibiting thigmonastic response.
Figure 2. Parts of makahiya.
Pulvini are responsible for the thigmonastic
response of makahiya. They are enlargements located at
the end of each pinnule, pinna and petiole, named as
tertiary, secondary, and main pulvinus respectively.
Figure 3. Tertiary, secondary and main pulvinus of
makahiya.
Each pulvinus has extensor cells located at the
upper portion and flexor cells at the lower portion.
Extensor cells contain sugar molecules while flexor cells
contain potassium ions and water. The turgidity of flexor
cells and flaccidity of extensor cells maintain the erect
position of pinnule, pinna or petiole before a stimulus.
Figure 4. Pulvinus before a stimulus.
Upon application of a stimulus, the flexor cells release the
potassium ions causing the water to flow out through
osmosis. The water then also flow towards the extensorcells through osmosis, due to the high sucrose content.
Figure 5. Pulvinus upon stimulation.
The turgidity of the extensor cells and the flaccidity of the
flexor cells now cause the pinnule, pinna or petiole to
droop.
Figure 6. Pulvinus after a stimulus.
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7/31/2019 Thig Mo Nasty
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Meanwhile, the release of potassium ions
triggers the neighboring pulvini to release their potassium
ions as well. This is comparable to the process of
propagation of action potential in an axon of a nerve cell.
Figure 7. Propagation of action potential in an axon of a
nerve cell.
Thus the stimulus causes the spread of the thigmonastic
response by the sequential drooping of the pinnules, pinna
and petioles.
The effect of heat stimulus on the apical and
lower parts of the plants was compared. A flame was
placed underneath the end of a pinna, causing a domino
effect on the drooping of pinnules, pinna and petioles.Several trials were done for the apical and lower stimulus.
In a selected recording of a trial in the lower
stimulus, seven pinna drooped for 34 seconds, some of
which are located at the other leaves. In another selected
recording of a trial in the apical stimulus, six pinna
drooped for 36 seconds, some of which are also located at
the other leaves. Thus for both parts, there was a
generalized response.
However, comparing the rest of the trials, there
were not as much significant difference in the number of
pinna which had drooped. This could be attributed to the
unequal application of heat stimulus and the wind whichcaused the heat to be dispersed. But the expected result is
that the lower stimulus should be more responsive than
the apical stimulus. Since the lower parts of makahiya are
more mature than the shoot parts, they should also have
bigger pulvini, thus creating more drastic spread of the
response.
The effect of touch stimulus on the uppermost
and lowermost pinnule was also compared. A pencil was
placed underneath the pinna and triggered an equal
amount of pressure for both locations in different
makahiya plants.
Figure 8. A pinnae after a touch stimulation of the
uppermost pinnule.
Figure 9. A pinnae after a touch stimulation of the
lowermost pinnule
The results showed a more drastic response
upon stimulation of the lowermost pinnule than the
uppermost pinnule, due to the difference of distances of
the origin of response from the secondary pulvinus. In the
lowermost pinnule, the stimulus was passed on to the
secondary pulvinus faster before it diminished, thus
triggering a more drastic response by drooping of the
entire leaf. In the uppermost pinnule, the stimulus
diminished before it had reached the secondary pulvinus,
thus triggering a faint response by drooping of some of the
pinnules.
In conclusion, the lower leaves and the
lowermost pinnule of makahiya showed a more drasticthigmonastic response. The possible adaptations of
thigmonasty are as follows:
protection less appetizing to herbivores less transpiration in hot conditions removal of harmful insects