Friday, May 1, 2015

Thigmomorphogenesis

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 :
 Anatomy
·         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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