Thigmomorphogenesis is from the Greek words “thigma” which means ‘to touch’; “morphê”
shape and “genesis” creation. Thus, thigmomorphogenesis is the response by
plants to mechanical sensation by altering their growth patterns, which may
include their canopy structure, growth rate, anatomy, morphology and mechanical
strength of their wood. The mechanical
sensation can be evinced by wind, raindrops, and rubbing by passing animals.
The term ‘thigmomorphogenesis’ was first coined by Mordecai
J. Jaffe. 1
Plant responses to mechanical sensation through reduction in
the rate of stem elongation, increase of stem diameter resulting in shorter and
stockier plants. Other responses include
alterations in chlorophyll content, hormone levels, biotic and abiotic stress resistance,
pithiness, flowering time, senescence, and stomata aperture. 2
1. Lansing
Funeral Home, 2007, The Lansing Star Online Obituaries, 14th
October, L-Star Publishing, Inc, NY. http://www.lansingstar.com/obituaries/3020-mordecai-j-qmarkq-jaffe
2. Biddington NL.1986, The Effects of Mechanically-Induced Stress in
Plants : A Review. Plant Growth Regulation 1986;4:103-123.
Observations & Studies
Theophrastus, a Greek who succeeded Aristotle in the
Peripatetic school, observed that trees growing in windy environments were
shorted in heights, shorter internodes, more knots, less straights, closer
grain, and harder wood.1
Charles Darwin reported a mechono-stimulus-induced plant
behaviour, where roots reorient their growth direction upon making contact with
barriers. 2
Free-swaying Pinus radiata
trees grew more in diameter over the lower part of the trunk than stayed trees.3
Salisbury reported that repeated touching of leaves of young
cocklebur plants caused a 30% inhibition in growth in
addition to an increase in rate of leaf senescence.
4
Moderate shaking of Liquidambar
trunks for 30 seconds daily reduced height growth to only 20 to 30 percent of
that of trees not shaken.5
Young plants of Hordeum
vulgare, Bryonia dioica, Cucumis sativus, Phaseolus vulgaris, Mimosa pudica and
Ricinus communis show retardation of growth when
given mechanical stimulus. 6
1. Theophrastus, 300 BCE, De
Causis Plantarum (On the Causes of Plants)
2. Darwin & Darwin, 1881, The Power of Movement in Plants
3. Jacobs, MR., 1954, The
effect of wind sway on the form and development of Pinus radiata D. Don, Australian Journal of Botany 2(1) 35 - 51
4. Salisbury FB, 1963, The Flowering Process, New York,
Macmillan.
5. Neel PL, Harris RW., 1971, Motion-induced inhibition of elongation and induction of dormancy in Liquidambar. Science. 1971 Jul
2;173(3991):58-9.
6. Jaffe MJ, 1973, Thigmomorphogenesis : The Response of Plant Growth and Development
to Mechanical Stimulation : With Special Reference to Bryonia dioica ., Planta 1973 Jun ; 114(2):145-57.
Doi:10.1007/BF000387472,
Summary of structural changes in acclimation to windy
environments :
·
Increase
in MFA
·
Increase
in grain angle
·
Increase
in cell division in direction of flexing
·
Increase
in wood density
·
Increase
in lignification ( higher S:G )
·
Decrease
in stiffness, more flexible
Morphology
·
Shorter
thicker stems ( Lower H:D )
·
Smaller
leaves
·
Shorter
internodes
·
Shorter
branches
·
Thicker
branch junctions
·
Streamlining
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